xref: /xsrc/external/mit/libSM/dist/doc/SMlib.xml

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
                   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">


<!-- lifted from troff+ms+XMan by doclifter -->
<book id="smlibms">

<bookinfo>
   <title>X Session Management Library</title>
   <subtitle>X Consortium Standard</subtitle>
   <releaseinfo>X Version 11, Release 6.4</releaseinfo>
   <authorgroup>
      <author>
         <firstname>Ralph</firstname><surname>Mor</surname>
      </author>
   </authorgroup>
   <corpname>X Consortium Standard</corpname>
   <copyright>
     <year>1993</year><year>1994</year>
     <holder>X Consortium</holder>
   </copyright>
   <releaseinfo>Version 1.0</releaseinfo>
   <affiliation><orgname>X Consortium</orgname></affiliation>
   <productnumber>X Version 11, Release 7</productnumber>

   <legalnotice>
     <para>
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
&ldquo;Software&rdquo;), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge,
publish, distribute, sublicense, and/or sell copies of the Software,
and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:
     </para>

     <para>
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
     </para>

     <para>
THE SOFTWARE IS PROVIDED &ldquo;AS IS&rdquo;, WITHOUT WARRANTY OF
ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
AND NONINFRINGEMENT.  IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR
ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     </para>

     <para>
Except as contained in this notice, the name of the X Consortium shall
not be used in advertising or otherwise to promote the sale, use or
other dealings in this Software without prior written authorization
from the X Consortium.
     </para>

     <para>
X Window System is a trademark of The Open Group.
     </para>
   </legalnotice>

</bookinfo>

<chapter id="overview_of_session_management">
  <title>Overview of Session Management</title>

  <abstract>
    <para>
The purpose of the X Session Management Protocol (<acronym>XSMP</acronym>)
is to provide a uniform mechanism for users to save and restore their
sessions.  A <firstterm>session</firstterm> is a group of clients,
each of which has a particular state.  The session is controlled by a
network service called the <firstterm>session manager</firstterm>.
The session manager issues commands to its clients on behalf of the
user.  These commands may cause clients to save their state or to
terminate.  It is expected that the client will save its state in such
a way that the client can be restarted at a later time and resume its
operation as if it had never been terminated.  A client's state might
include information about the file currently being edited, the current
position of the insertion point within the file, or the start of an
uncommitted transaction.  The means by which clients are restarted is
unspecified by this protocol.
    </para>

    <para>
For purposes of this protocol, a <firstterm>client</firstterm> of the
session manager is defined as a connection to the session manager.  A
client is typically, though not necessarily, a process running an
application program connected to an X display.  However, a client may
be connected to more than one X display or not be connected to any X
displays at all.
    </para>
  </abstract>
</chapter>

<chapter id='the_session_management_library'>
  <title>The Session Management Library</title>
  <abstract>
    <para>
The Session Management Library (<abbrev>SMlib</abbrev>) is a low-level
"C" language interface to XSMP.  It is expected that higher level
toolkits, such as Xt, will hide many of the details of session
management from clients.  Higher level toolkits might also be developed
for session managers to use, but no such effort is currently under way.
    </para>
  </abstract>

  <para>
    SMlib has two parts to it:
    <itemizedlist mark='bullet'>
      <listitem><para>One set of functions for clients that want to be part of a session</para></listitem>
      <listitem><para>One set of functions for session managers to call</para></listitem>
    </itemizedlist>
  </para>

  <para>
Some applications will use both sets of functions and act as
<firstterm>nested session managers</firstterm>.  That is, they will be
both a session manager and a client of another session.  An example is
a mail program that could start a text editor for editing the text of
a mail message.  The mail program is part of a regular session and, at
the same time, is also acting as a session manager to the editor.
  </para>

  <para>
Clients initialize by connecting to the session manager and obtaining
a <firstterm>client-ID</firstterm> that uniquely identifies them in
the session.  The session manager maintains a list of properties for
each client in the session.  These properties describe the client's
environment and, most importantly, describe how the client can be
restarted (via an <property>SmRestartCommand</property>). Clients are
expected to save their state in such a way as to allow multiple
instantiations of themselves to be managed independently.  For
example, clients may use their client-ID as part of a filename in
which to store the state for a particular instantiation.  The
client-ID should be saved as part of the <property>SmRestartCommand</property>
so that the client will retain the same ID after it is restarted.
  </para>

  <para>
Once the client initializes itself with the session manager, it must
be ready to respond to messages from the session manager.  For
example, it might be asked to save its state or to terminate.  In the
case of a shutdown, the session manager might give each client a
chance to interact with the user and cancel the shutdown.
  </para>
</chapter>

<chapter id='understanding_smlibs_dependence_on_ice'>
  <title>Understanding SMlib's Dependence on ICE</title>

  <para>
The X Session Management Protocol is layered on top of the
Inter-Client Exchange (<acronym>ICE</acronym>) Protocol.  The ICE
protocol is designed to multiplex several protocols over a single
connection.  As a result, working with SMlib requires a little
knowledge of how the ICE library works.
  </para>

  <para>
The ICE library utilizes callbacks to process messages.  When a client
detects that there is data to read on an ICE connection, it should
call the <function>IceProcessMessages</function> function.
<function>IceProcessMessages</function> will read the message header
and look at the major opcode in order to determine which protocol the
message was intended for.  The appropriate protocol library will then
be triggered to unpack the message and hand it off to the client via a
callback.
  </para>

  <para>
The main point to be aware of is that an application using SMlib must
have some code that detects when there is data to read on an ICE
connection.  This can be done via a <function>select</function> call
on the file descriptor for the ICE connection, but more
typically, <function>XtAppAddInput</function> will be used to register
a callback that will invoke <function>IceProcessMessages</function>
each time there is data to read on the ICE connection.
  </para>

  <para>
To further complicate things, knowing which file descriptors to
call <function>select</function> on requires an understanding of how
ICE connections are created.  On the client side, a call must be made
to <function>SmcOpenConnection</function> in order to open a connection
with a session manager.  <function>SmcOpenConnection</function> will
internally makea call into <function>IceOpenConnection</function>
which will, in turn, determine if an ICE connection already exists
between the client and session manager.  Most likely, a connection
will not already exist and a new ICE connection will be created.  The
main point to be aware of is that, on the client side, it is not
obvious when ICE connections get created or destroyed, because
connections are shared when possible.  To deal with this, the ICE
library lets the application register watch procedures that will be
invoked each time an ICE connection is opened or closed.  These watch
procedures could be used to add or remove ICE file descriptors from
the list of descriptors to call <function>select</function> on.
  </para>

  <para>
On the session manager side, things work a bit differently.  The
session manager has complete control over the creation of ICE
connections.  The session manager has to first
call <function>IceListenForConnections</function> in order to start
listening for connections from clients.  Once a connection attempt is
detected, <function>IceAcceptConnection</function> must be called, and
the session manager can simply add the new ICE file descriptor to the
list of descriptors to call <function>select</function> on.

  </para>

  <para>
For further information on the library functions related to ICE connections,
see the <citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
  </para>
</chapter>

<chapter id='header_files_and_library_name'>
<title>Header Files and Library Name</title>

  <para>
Applications (both session managers and clients) should include the
header file &lt;<filename class='headerfile'>X11/SM/SMlib.h</filename>&gt;.
This header file defines all of the SMlib data structures and function
prototypes.  <filename class='headerfile'>SMlib.h</filename> includes the
header file &lt;<filename class='headerfile'>X11/SM/SM.h</filename>&gt;,
which defines all of the SMlib constants.
  </para>

  <para>
Because SMlib is dependent on ICE, applications should link against
SMlib and ICElib by using
<quote><option>-lSM</option> <option>-lICE</option></quote>.
  </para>
</chapter>

<chapter id='session_management_client'>
  <title>Session Management Client (<acronym>Smc</acronym>) Functions</title>

  <para>
    This section discusses how Session Management clients:
    <itemizedlist mark='bullet'>
      <listitem><para>Connect to the Session Manager</para></listitem>
      <listitem><para>Close the connection</para></listitem>
      <listitem><para>Modify callbacks</para></listitem>
      <listitem><para>Set, delete, and retrieve Session Manager properties</para></listitem>
      <listitem><para>Interact with the user</para></listitem>
      <listitem><para>Request a &ldquo;Save Yourself&rdquo;</para></listitem>
      <listitem><para>Request a &ldquo;Save Yourself Phase 2&rdquo;</para></listitem>
      <listitem><para>Complete a &ldquo;Save Yourself&rdquo;</para></listitem>
      <listitem><para>Use Smc informational functions</para></listitem>
      <listitem><para>Handle Errors</para></listitem>
    </itemizedlist>
  </para>

  <sect1 id='connecting_to_the_session_manager'>
    <title>Connecting to the Session Manager</title>

    <para>
To open a connection with a session manager,
use <function>SmcOpenConnection</function>
    </para>

    <funcsynopsis>
      <funcprototype>
	<funcdef>SmcConn <function>SmcOpenConnection</function></funcdef>
	<paramdef>char *<parameter>network_ids_list</parameter></paramdef>
	<paramdef>SmPointer <parameter>context</parameter></paramdef>
	<paramdef>int <parameter>xsmp_major_rev</parameter></paramdef>
	<paramdef>int <parameter>xsmp_minor_rev</parameter></paramdef>
	<paramdef>unsigned long <parameter>mask</parameter></paramdef>
	<paramdef>SmcCallbacks *<parameter>callbacks</parameter></paramdef>
	<paramdef>char *<parameter>previous_id</parameter></paramdef>
	<paramdef>char **<parameter>client_id_ret</parameter></paramdef>
	<paramdef>int <parameter>error_length</parameter></paramdef>
	<paramdef>char *<parameter>error_string_ret</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>

    <variablelist remap='IP'>
      <varlistentry>
	<term><parameter>network_ids_list</parameter></term>
	<listitem><para>Specifies the network ID(s) of the session manager.</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>context</parameter></term>
	<listitem><para>
A pointer to an opaque object or <constant>NULL</constant>.  Used to determine
if an ICE connection can be shared
(see <link linkend='context_sharing'>below</link>).
     </para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>xsmp_major_rev</parameter></term>
	<listitem><para>
The highest major version of the XSMP the application supports.
	</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>xsmp_minor_rev</parameter></term>
	<listitem><para>
The highest minor version of the XSMP the application supports (for
the specified <parameter>xsmp_major_rev</parameter>).
	</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>mask</parameter></term>
	<listitem><para>A mask indicating which callbacks to register.</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>callbacks</parameter></term>
	<listitem><para>
The callbacks to register.  These callbacks are used to respond to
messages from the session manager.
	</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>previous_id</parameter></term>
	<listitem><para>The client ID from the previous session.</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>client_id_ret</parameter></term>
	<listitem><para>The client ID for the current session is returned.</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>error_length</parameter></term>
	<listitem><para>Length of the <parameter>error_string_ret</parameter> argument passed in.</para></listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>error_string_ret</parameter></term>
	<listitem><para>
Returns a null-terminated error message, if any.
The <parameter>error_string_ret</parameter> argument points to user supplied
memory.  No more than <parameter>error_length</parameter> bytes are used.
	</para></listitem>
      </varlistentry>
    </variablelist>

    <para>
The <parameter>network_ids_list</parameter> argument is a
null-terminated string containing a list of network IDs for the session
manager, separated by commas. If <parameter>network_ids_list</parameter>
is <constant>NULL</constant>, the value of
the <envar>SESSION_MANAGER</envar> environment variable will be used.
Each network ID has the following format:

<informaltable pgwide='0' frame='none'>
  <tgroup cols='3' align='center'>
    <colspec colname='c1'/>
    <colspec colname='c2'/>
    <colspec colname='c3'/>
    <tbody>
      <row>
        <entry align='left'></entry>
        <entry align='left'><literal>tcp/</literal><parameter>&lt;hostname&gt;</parameter><literal>:</literal><parameter>&lt;portnumber&gt;</parameter></entry>
        <entry align='left'>or</entry>
      </row>
      <row>
        <entry align='left'></entry>
        <entry align='left'><literal>decnet/</literal><parameter>&lt;hostname&gt;</parameter><literal>::</literal><parameter>&lt;objname&gt;</parameter></entry>
        <entry align='left'>or</entry>
      </row>
      <row>
        <entry align='left'></entry>
        <entry align='left'><literal>local/</literal><parameter>&lt;hostname&gt;</parameter><literal>:</literal><parameter>&lt;path&gt;</parameter></entry>
        <entry align='left'></entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>
    </para>

    <para>
An attempt will be made to use the first network ID.  If that fails,
an attempt will be made using the second network ID, and so on.
    </para>

    <para>
After the connection is established, <function>SmcOpenConnection</function>
registers the client with the session manager.  If the client is being
restarted from a previous session, <parameter>previous_id</parameter>
should contain a null terminated string representing the client ID from the
previous session.  If the client is first joining the session,
<parameter>previous_id</parameter> should be set to <constant>NULL</constant>.
If <parameter>previous_id</parameter> is specified but is determined
to be invalid by the session manager, SMlib will re-register the
client with <parameter>previous_id</parameter> set to <constant>NULL</constant>.
    </para>

    <para>
If <function>SmcOpenConnection</function> succeeds, it returns an
opaque connection pointer of type <function>SmcConn</function> and the
<parameter>client_id_ret</parameter> argument contains the client ID to be
used for this session.  The <parameter>client_id_ret</parameter> should be
freed with a call to <function>free</function> when no longer needed.  On
failure, <function>SmcOpenConnection</function> returns
<constant>NULL</constant>, and the reason for failure is returned in
<parameter>error_string_ret</parameter>.
    </para>

    <para>
Note that SMlib uses the ICE protocol to establish a connection with
the session manager.  If an ICE connection already exists between the
client and session manager, it might be possible for the same ICE
connection to be used for session management.
    </para>

    <para id='context_sharing'>
The context argument indicates how willing the client is to share the
ICE connection with other protocols.  If context is <constant>NULL</constant>,
then the caller is always willing to share the connection.  If context is not
<constant>NULL</constant>, then the caller is not willing to use a previously
opened ICE connection that has a different non-<constant>NULL</constant>
context associated with it.
    </para>

    <para>
As previously discussed
(<link linkend='understanding_smlibs_dependence_on_ice'>section 3,
&ldquo;Understanding SMlib's Dependence on ICE&rdquo;</link>), the
client will have to keep track of when ICE connections are created or
destroyed (using <function>IceAddConnectionWatch</function>
and <function>IceRemoveConnectionWatch</function> and will have to
call <function>IceProcessMessages</function> each time
a <function>select</function> shows that there is data to read on an
ICE connection.  For further information, see the
<citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
    </para>

    <para>
The callbacks argument contains a set of callbacks used to respond to
session manager events.  The mask argument specifies which callbacks
are set.  All of the callbacks specified in this version of SMlib are
mandatory.  The mask argument is necessary in order to maintain
backwards compatibility in future versions of the library.
    </para>

    <para>
The following values may be ORed together to obtain a
<parameter>mask</parameter> value:

      <simplelist type='vert'>
	<member><constant>SmcSaveYourselfProcMask</constant></member>
	<member><constant>SmcDieProcMask</constant></member>
	<member><constant>SmcSaveCompleteProcMask</constant></member>
	<member><constant>SmcShutdownCancelledProcMask</constant></member>
      </simplelist>
    </para>

    <para>
For each callback, the client can register a pointer to client data.
When SMlib invokes the callback, it will pass the client data pointer.
    </para>

<!-- .ne 4  IGNORED -->

<synopsis>
typedef struct {

	struct {
		SmcSaveYourselfProc callback;
		SmPointer client_data;
	} save_yourself;

	struct {
		SmcDieProc callback;
		SmPointer client_data;
	} die;

	struct {
		SmcSaveCompleteProc callback;
		SmPointer client_data;
	} save_complete;

	struct {
		SmcShutdownCancelledProc callback;
		SmPointer client_data;
	} shutdown_cancelled;

} SmcCallbacks;
</synopsis>

    <sect2 id='the_save_yourself_callback'>
      <title>The Save Yourself Callback</title>

      <para>
The Save Yourself callback is of type <function>SmcSaveYourselfProc</function>
      </para>

<funcsynopsis>
<funcprototype>
  <funcdef>typedef void (*<function>SaveYourselfProc</function>)</funcdef>
    <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
    <paramdef>SmcConn <parameter>client_data</parameter></paramdef>
    <paramdef>int <parameter>save_type</parameter></paramdef>
    <paramdef>Bool <parameter>shutdown</parameter></paramdef>
    <paramdef>int <parameter>interact_style</parameter></paramdef>
    <paramdef>Bool <parameter>fast</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>Client data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>save_type</parameter></term>
    <listitem><para>Specifies the type of information that should be saved.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>shut_down</parameter></term>
    <listitem><para>Specifies if a shutdown is taking place.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>interact_style</parameter></term>
    <listitem><para>The type of interaction allowed with the user.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>fast</parameter></term>
    <listitem><para>if <symbol>True</symbol>, then client should save its state as quickly as possible.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The session manager sends a &ldquo;Save Yourself&rdquo; message to a
client either to checkpoint it or just before termination so that it
can save its state.  The client responds with zero or more calls
to <function>SmcSetProperties</function> to update the properties
indicating how to restart the client.  When all the properties have
been set, the client calls <function>SmcSaveYourselfDone</function>
      </para>

      <para>
If <parameter>interact_style</parameter> is
<constant>SmInteractStyleNone</constant> the
client must not interact with the user while saving state.
If <parameter>interact_style</parameter> is
<constant>SmInteractStyleErrors</constant> the
client may interact with the user only if an error condition arises.
If <parameter>interact_style</parameter> is
<constant>SmInteractStyleAny</constant> then the
client may interact with the user for any purpose.  Because only one
client can interact with the user at a time, the client must
call <function>SmcInteractRequest</function> and wait for an
&ldquo;Interact&rdquo; message from the session manager.  When the
client is done interacting with the user, it
calls <function>SmcInteractDone</function> The client may only
call <function>SmcInteractRequest</function> after it receives a
&ldquo;Save Yourself&rdquo; message and before it
calls <function>SmcSaveYourselfDone</function>
      </para>

      <para>
If <parameter>save_type</parameter> is <constant>SmSaveLocal</constant> the
client must update the properties to reflect its current state.  Specifically,
it should save enough information to restore the state as seen by the
user of this client.  It should not affect the state as seen by other users.
If <parameter>save_type</parameter> is <constant>SmSaveGlobal</constant>
the user wants the client to commit all of its data to permanent, globally
accessible storage.
If <parameter>save_type</parameter> is <constant>SmSaveBoth</constant>
the client should do both of these (it should first commit the data to
permanent storage before updating its properties).
      </para>

      <para>
Some examples are as follows:

        <itemizedlist mark='bullet'>
	  <listitem><para>
If a word processor were sent a &ldquo;Save Yourself&rdquo; with a
type of <constant>SmSaveLocal</constant> it could create a temporary
file that included the current contents of the file, the location of
the cursor, and other aspects of the current editing session.  It
would then update its <property>SmRestartCommand</property> property with
enough information to find this temporary file.
	  </para></listitem>
	  <listitem><para>
If a word processor were sent a &ldquo;Save Yourself&rdquo; with a
type of <constant>SmSaveGlobal</constant> it would simply save the
currently edited file.
	  </para></listitem>
	  <listitem><para>
If a word processor were sent a &ldquo;Save Yourself&rdquo; with a
type of <constant>SmSaveBoth</constant> it would first save the
currently edited file.  It would then create a temporary file with
information such as the current position of the cursor and what file
is being edited.  Finally, it would update its
<property>SmRestartCommand</property> property with enough information
to find the temporary file.
	  </para></listitem>
	</itemizedlist>
      </para>

      <para>
The <parameter>shutdown</parameter> argument specifies whether the
system is being shut down.
The interaction is different depending on whether or not shutdown is
set.  If not shutting down, the client should save its state and wait
for a &ldquo;Save Complete&rdquo; message.  If shutting down, the
client must save state and then prevent interaction until it receives
either a &ldquo;Die&rdquo; or a &ldquo;Shutdown Cancelled.&rdquo;
      </para>

      <para>
The <parameter>fast</parameter> argument specifies that the client
should save its state as quickly as possible.  For example, if the
session manager knows that power is about to fail, it would
set <parameter>fast</parameter> to <constant>True</constant>.
      </para>
    </sect2>

    <sect2 id='the_die_callback'>
      <title>The Die Callback</title>

      <para>
The Die callback is of type <function>SmcDieProc</function>
      </para>

<funcsynopsis>
<funcprototype>
  <funcdef>typedef void (*<function>SmcDieProc</function>)</funcdef>
    <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
    <paramdef>SmcConn <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>Client data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>


      <para>
The session manager sends a &ldquo;Die&rdquo; message to a client when
it wants it to die.  The client should respond by calling
<function>SmcCloseConnection</function>.  A session manager that
behaves properly will send a &ldquo;Save Yourself&rdquo; message
before the &ldquo;Die&rdquo; message.
      </para>
    </sect2>

    <sect2 id='the_save_complete_callback'>
      <title>The Save Complete Callback</title>

      <para>
The Save Complete callback is of type <function>SmcSaveCompleteProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmcSaveCompleteProc</function>)</funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>Client data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>
    </sect2>


    <sect2 id='the_shutdown_cancelled_callback'>
      <title>The Shutdown Cancelled Callback</title>

      <para>
The Shutdown Cancelled callback is of type
<function>SmcShutdownCancelledProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmcShutdownCancelledProc</function>)</funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>Client data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The session manager sends a &ldquo;Shutdown Cancelled&rdquo; message
when the user cancelled the shutdown during an interaction
(see <link linkend='interacting_with_the_user'>section 5.5,
&ldquo;Interacting With the User&rdquo;</link>).  The client can now
continue as if the shutdown had never happened.  If the client has not
called <function>SmcSaveYourselfDone</function> yet, it can either
abort the save and then call <function>SmcSaveYourselfDone</function>
with the success argument set to <constant>False</constant> or it can
continue with the save and then call <function>SmcSaveYourselfDone</function>
with the <parameter>success</parameter> argument set to reflect the outcome
of the save.
      </para>
    </sect2>
  </sect1>

  <sect1 id='closing_the_connection'><title>Closing the Connection</title>

    <para>
To close a connection with a session manager,
use <function>SmcCloseConnection</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>SmcCloseStatus <function>SmcCloseConnection</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>int <parameter>count</parameter></paramdef>
      <paramdef>char **<parameter>reason_msgs</parameter></paramdef>
  </funcprototype>
</funcsynopsis>
<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>count</parameter></term>
    <listitem><para>The number of reasons for closing the connection.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>reason_msgs</parameter></term>
    <listitem><para>The reasons for closing the connection.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The <parameter>reason_msgs</parameter> argument will most likely be
<constant>NULL</constant> if resignation is expected by the client.
Otherwise, it contains a list of null-terminated Compound Text strings
representing the reason for termination.  The session manager should
display these reason messages to the user.
    </para>

    <para>
Note that SMlib used the ICE protocol to establish a connection with
the session manager, and various protocols other than session
management may be active on the ICE connection.
When <function>SmcCloseConnection</function> is called, the ICE
connection will be closed only if all protocols have been shutdown on
the connection.  Check the ICElib standard
for <function>IceAddConnectionWatch</function>
and <function>IceRemoveConnectionWatch</function> to learn how to set
up a callback to be invoked each time an ICE connection is opened or
closed.  Typically this callback adds/removes the ICE file descriptor
from the list of active descriptors to call <function>select</function> on
(or calls <function>XtAppAddInput</function> or
<function>XtRemoveInput</function>).
    </para>


    <para>
<function>SmcCloseConnection</function> returns one of the following values:

      <itemizedlist mark='bullet'>
	<listitem><para>
<constant>SmcClosedNow</constant> - the ICE connection was closed at
this time, the watch procedures were invoked, and the connection was freed.
	</para></listitem>
	<listitem><para>
<constant>SmcClosedASAP</constant> - an IO error had occurred on the
connection, but <function>SmcCloseConnection</function> is being
called within a nested <function>IceProcessMessages</function> The
watch procedures have been invoked at this time, but the connection
will be freed as soon as possible (when the nesting level reaches zero
and <function>IceProcessMessages</function> returns a status
of <function>IceProcessMessagesConnectionClosed</function>
	</para> </listitem>
	<listitem><para>
<constant>SmcConnectionInUse</constant> - the connection was not closed at
this time, because it is being used by other active protocols.
	</para> </listitem>
      </itemizedlist>
    </para>
  </sect1>


  <sect1 id='modifying_callbacks'>
    <title>Modifying Callbacks</title>

    <para>
To modify callbacks set up in <function>SmcOpenConnection</function>
use <function>SmcModifyCallbacks</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcModifyCallbacks</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>unsigned long <parameter>mask</parameter></paramdef>
      <paramdef>SmcCallbacks *<parameter>callbacks</parameter></paramdef>
  </funcprototype>
</funcsynopsis>
<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>mask</parameter></term>
    <listitem><para>A mask indicating which callbacks to modify.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>callbacks</parameter></term>
    <listitem><para>The new callbacks.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
When specifying a value for the <parameter>mask</parameter> argument,
the following values may be ORed together:

      <simplelist type='vert'>
	<member><constant>SmcSaveYourselfProcMask</constant></member>
	<member><constant>SmcDieProcMask</constant></member>
	<member><constant>SmcSaveCompleteProcMask</constant></member>
	<member><constant>SmcShutdownCancelledProcMask</constant></member>
      </simplelist>
    </para>
  </sect1>

  <sect1 id='setting_deleting_and_retrieving_session_management_properties'>
    <title>Setting, Deleting, and Retrieving Session Management Properties</title>

    <para>
To set session management properties for this client,
use <function>SmcSetProperties</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcSetProperties</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>SmProp **<parameter>props</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>props</parameter></term>
    <listitem><para>The list of properties to set.</para></listitem>
  </varlistentry>
</variablelist>


    <para>
The properties are specified as an array of property pointers.
Previously set property values may be over-written using
the <function>SmcSetProperties</function> function.  Note that the
session manager is not expected to restore property values when the
session is restarted.  Because of this, clients should not try to use
the session manager as a database for storing application specific state.
    </para>

    <para>
For a description of session management properties and
the <structname>SmProp</structname> structure,
see <link linkend='session_management_properties'>section 7,
&ldquo;Session Management Properties.&rdquo;</link>
    </para>


    <para>
To delete properties previously set by the client,
use <function>SmcDeleteProperties</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcDeleteProperties</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>char **<parameter>prop_names</parameter></paramdef>
  </funcprototype>
</funcsynopsis>
<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>prop_names</parameter></term>
    <listitem><para>The list of properties to set.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
To get properties previously stored by the client,
use <function>SmcGetProperties</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>Status <function>SmcGetProperties</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmcPropReplyProc <parameter>prop_reply_proc</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>prop_reply_proc</parameter></term>
    <listitem><para>The callback to be invoked when the properties reply comes back.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>This pointer to client data will be passed to the <function>SmcPropReplyProc</function> callback.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The return value of <function>SmcGetProperties</function> is zero for
failure and a positive value for success.
    </para>

    <para>
Note that the library does not block until the properties reply comes
back.  Rather, a callback of type <function>SmcPropReplyProc</function>
is invoked when the data is ready.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmcPropReplyProc</function>)</funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>SmProp **<parameter>props</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>This pointer to client data will be passed to the <function>SmcPropReplyProc</function> callback.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties returned.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>props</parameter></term>
    <listitem><para>The list of properties returned.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
To free each property, use <function>SmFreeProperty</function>
(see <link linkend='freeing_data'>section 8, &ldquo;Freeing
Data&rdquo;</link>).  To free the actual array of pointers,
use <function>free</function>
    </para>
  </sect1>

  <sect1 id='interacting_with_the_user'>
    <title>Interacting With the User</title>

    <para>
After receiving a &ldquo;Save Yourself&rdquo; message with an
<parameter>interact_style</parameter> of
<constant>SmInteractStyleErrors</constant>
or <constant>SmInteractStyleAny</constant> the client may choose to
interact with the user.  Because only one client can interact with the
user at a time, the client must call <function>SmcInteractRequest</function>
and wait for an &ldquo;Interact&rdquo; message from the session manager.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>Status <function>SmcInteractRequest</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>int <parameter>dialog_type</parameter></paramdef>
      <paramdef>SmcInteractProc <parameter>interact_proc</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>dialog_type</parameter></term>
    <listitem><para>The type of dialog the client wishes to present to the user.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>interact_proc</parameter></term>
    <listitem><para>The callback to be invoked when the &ldquo;Interact&rdquo; message arrives from the session manager.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>
This pointer to client data will be passed to
the <function>SmcInteractProc</function> callback when the
&ldquo;Interact&rdquo; message arrives.
    </para></listitem>
  </varlistentry>
</variablelist>

    <para>
The return value of <function>SmcInteractRequest</function> is zero
for failure and a positive value for success.
    </para>

    <para>
The <parameter>dialog_type</parameter> argument specifies
either <constant>SmDialogError</constant> indicating that the client
wants to start an error dialog, or <constant>SmDialogNormal</constant>
meaning that the client wishes to start a nonerror dialog.
    </para>

    <para>
Note that if a shutdown is in progress, the user may have the option
of cancelling the shutdown.  If the shutdown is cancelled, the clients
that have not interacted yet with the user will receive a
&ldquo;Shutdown Cancelled&rdquo; message instead of the
&ldquo;Interact&rdquo; message.
    </para>

    <para>
The <function>SmcInteractProc</function> callback will be invoked when
the &ldquo;Interact&rdquo; message arrives from the session manager.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmcInteractProc</function>)</funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>Client data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
After interacting with the user (in response to an &ldquo;Interact&rdquo;
message), you should call <function>SmcInteractDone</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcInteractDone</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>Bool <parameter>cancel_shutdown</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>cancel_shutdown</parameter></term>
    <listitem><para>If <constant>True</constant>, indicates that the user requests that the entire shutdown be cancelled.</para></listitem>
  </varlistentry>
</variablelist>
    <para>
The <parameter>cancel_shutdown</parameter> argument may only be
<constant>True</constant> if the corresponding &ldquo;Save Yourself&rdquo;
specified <constant>True</constant> for shutdown
and <constant>SmInteractStyleErrors</constant>
or <constant>SmInteractStyleAny</constant> for
the <parameter>interact_style</parameter>.
    </para>
  </sect1>

  <sect1 id='requesting_a_save_yourself'>
    <title>Requesting a Save Yourself</title>

    <para>
To request a checkpoint from the session manager,
use <function>SmcRequestSaveYourself</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcRequestSaveYourself</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>int <parameter>save_type</parameter></paramdef>
      <paramdef>Bool <parameter>shutdown</parameter></paramdef>
      <paramdef>int <parameter>interact_style</parameter></paramdef>
      <paramdef>Bool <parameter>fast</parameter></paramdef>
      <paramdef>Bool <parameter>global</parameter></paramdef>
  </funcprototype>
</funcsynopsis>


<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>save_type</parameter></term>
    <listitem><para>Specifies the type of information that should be saved.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>shutdown</parameter></term>
    <listitem><para>Specifies if a shutdown is taking place.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>interact_style</parameter></term>
    <listitem><para>The type of interaction allowed with the user.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>fast</parameter></term>
    <listitem><para>If <constant>True</constant> the client should save its state as quickly as possible.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>global</parameter></term>
    <listitem><para>Controls who gets the &ldquo;Save Yourself.&rdquo;</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The <parameter>save_type</parameter>, <parameter>shutdown</parameter>,
<parameter>interact_style</parameter>, and <parameter>fast</parameter>
arguments are discussed in more detail in
<link linkend='the_save_yourself_callback'>section 5.1.1,
&ldquo;The Save Yourself Callback.&rdquo;</link>
    </para>

    <para>
If <parameter>global</parameter> is set to <constant>True</constant> then
the resulting &ldquo;Save Yourself&rdquo; should be sent to all clients in the
session.  For example, a vendor of a Uninterruptible Power Supply
(<acronym>UPS</acronym>) might include a Session Management client
that would monitor the status of the UPS and generate a fast shutdown
if the power is about to be lost.
    </para>

    <para>
If global is set to <constant>False</constant> then the &ldquo;Save
Yourself&rdquo; should only be sent to the client that requested it.
    </para>
  </sect1>

  <sect1 id='requesting_a_save_yourself_phase_2'>
    <title>Requesting a Save Yourself Phase 2</title>

    <para>
In response to a &ldquo;Save Yourself&rdquo;, the client may request to be
informed when all the other clients are quiescent so that it can save their
state.  To do so, use <function>SmcRequestSaveYourselfPhase2</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>Status <function>SmcRequestSaveYourselfPhase2</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>SmcSaveYourselfPhase2Proc <parameter>save_yourself_phase2_proc</parameter></paramdef>
      <paramdef>SmPointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>save_type_phase2_proc</parameter></term>
    <listitem><para>The callback to be invoked when the &ldquo;Save Yourself Phase 2&rdquo; message arrives from the session manager.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>This pointer to client data will be passed to the <function>SmcSaveYourselfPhase2Proc</function> callback when the &ldquo;Save Yourself Phase 2&rdquo; message arrives.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The return value of <function>SmcRequestSaveYourselfPhase2</function>
is zero for failure and a positive value for success.
    </para>

    <para>
This request is needed by clients that manage other clients (for
example, window managers, workspace managers, and so on).  The manager
must make sure that all of the clients that are being managed are in
an idle state so that their state can be saved.
    </para>
  </sect1>

  <sect1 id='completing_a_save_yourself'>
    <title>Completing a Save Yourself</title>

    <para>
After saving state in response to a &ldquo;Save Yourself&rdquo;
message, you should call <function>SmcSaveYourselfDone</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmcSaveYourselfDone</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>Bool <parameter>success</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>success</parameter></term>
    <listitem><para>If <constant>True</constant> the &ldquo;Save Yourself&rdquo; operation was completed successfully.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
Before calling <function>SmcSaveYourselfDone</function> the client
must have set each required property at least once since the client
registered with the session manager.
    </para>
  </sect1>

  <sect1 id='using_smc_informational_functions'>
    <title>Using Smc Informational Functions</title>

<funcsynopsis>
   <funcprototype>
      <funcdef>int <function>SmcProtocolVersion</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcProtocolVersion</function> returns the major version of
the session management protocol associated with this session.
    </para>


<funcsynopsis>
   <funcprototype>
      <funcdef>int <function>SmcProtocolRevision</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcProtocolRevision</function> returns the minor version of
the session management protocol associated with this session.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmcVendor</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcVendor</function> returns a string that provides some
identification of the owner of the session manager.  The string should
be freed with a call to <function>free</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmcRelease</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcRelease</function> returns a string that provides the
release number of the session manager.  The string should be freed
with a call to <function>free</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmcClientID</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcClientID</function> returns a null-terminated string for
the client ID associated with this connection.  This information was
also returned in <function>SmcOpenConnection</function> (it is
provided here for convenience).  Call <function>free</function> on
this pointer when the client ID is no longer needed.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>IceConn <function>SmcGetIceConnection</function></funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmcGetIceConnection</function> returns the ICE connection
object associated with this session management connection object.  The
ICE connection object can be used to get some additional information
about the connection.  Some of the more useful functions which can be
used on the IceConn are <function>IceConnectionNumber</function>,
<function>IceConnectionString</function>,
<function>IceLastSentSequenceNumber</function>,
<function>IceLastReceivedSequenceNumber</function>,
and <function>IcePing</function>. For further information, see
the <citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
    </para>
  </sect1>

  <sect1 id='error_handling'>
    <title>Error Handling</title>

    <para>
If the client receives an unexpected protocol error from the session
manager, an error handler is invoked by SMlib.  A default error
handler exists that simply prints the error message
to <varname>stderr</varname> and exits if the severity of the error
is fatal.  The client can change this error handler by calling
the <function>SmcSetErrorHandler</function> function.
    </para>

<funcsynopsis>
  <funcprototype>
      <funcdef>SmcErrorHandler <function>SmcSetErrorHandler</function></funcdef>
      <paramdef>SmcErrorHandler <parameter>handler</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
The error handler.  You should pass <constant>NULL</constant> to
restore the default handler.
    </para>


    <para>
<function>SmcSetErrorHandler</function> returns the previous error handler.
    </para>

    <para>
The <function>SmcErrorHandler</function> has the following type:
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmcErrorHandler</function>)</funcdef>
      <paramdef>SmcConn <parameter>smc_conn</parameter></paramdef>
      <paramdef>Bool <parameter>swap</parameter></paramdef>
      <paramdef>int <parameter>offending_minor_opcode</parameter></paramdef>
      <paramdef>unsigned long <parameter>offending_sequence_num</parameter></paramdef>
      <paramdef>int <parameter>error_class</parameter></paramdef>
      <paramdef>int <parameter>severity</parameter></paramdef>
      <paramdef>IcePointer <parameter>values</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>smc_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>swap</parameter></term>
     <listitem><para>A flag that indicates if the specified values need byte swapping.</para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>offending_minor_opcode</parameter></term>
     <listitem><para>The minor opcode of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>offending_sequence_num</parameter></term>
     <listitem><para>The sequence number of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>error_class</parameter></term>
     <listitem><para>The error class of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>severity</parameter></term>
     <listitem><para><constant>IceCanContinue</constant>,
	 <constant>IceFatalToProtocol</constant>, or
	 <constant>IceFatalToConnection</constant>
     </para></listitem>
  </varlistentry>
  <varlistentry>
     <term><parameter>values</parameter></term>
     <listitem><para>Any additional error values specific to the minor opcode and class.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
Note that this error handler is invoked for protocol related errors.
To install an error handler to be invoked when an IO error occurs, use
<function>IceSetIOErrorHandler</function> For further information, see
the <citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
    </para>
  </sect1>
</chapter>

<chapter id='session_management_server'>
  <title>Session Management Server (<acronym>Sms</acronym>) Functions</title>

  <para>
This section discusses how Session Management servers:

    <itemizedlist mark='bullet'>
      <listitem><para>Initialize the library</para></listitem>
      <listitem><para>Register the client</para></listitem>
      <listitem><para>Send a &ldquo;Save Yourself&rdquo; message</para></listitem>
      <listitem><para>Send a &ldquo;Save Yourself Phase 2&rdquo; message</para></listitem>
      <listitem><para>Send an &ldquo;Interact&rdquo; message</para></listitem>
      <listitem><para>Send a &ldquo;Save Complete&rdquo; message</para></listitem>
      <listitem><para>Send a &ldquo;Die&rdquo; message</para></listitem>
      <listitem><para>Cancel a shutdown</para></listitem>
      <listitem><para>Return properties</para></listitem>
      <listitem><para>Ping a client</para></listitem>
      <listitem><para>Clean up after a client disconnects</para></listitem>
      <listitem><para>Use Sms informational functions</para></listitem>
      <listitem><para>Handle errors</para></listitem>
    </itemizedlist>
  </para>

  <sect1 id='initializing_the_library'>
    <title>Initializing the Library</title>

    <para>
<function>SmsInitialize</function> is the first SMlib function that
should be called by a session manager.  It provides information about
the session manager and registers a callback that will be invoked each
time a new client connects to the session manager.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>Status <function>SmsInitialize</function></funcdef>
      <paramdef>char *<parameter>vendor</parameter></paramdef>
      <paramdef>char *<parameter>release</parameter></paramdef>
      <paramdef>SmsNewClientProc <parameter>new_client_proc</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>IceHostBasedAuthProc <parameter>host_based_auth_proc</parameter></paramdef>
      <paramdef>int <parameter>error_length</parameter></paramdef>
      <paramdef>char *<parameter>error_string_ret</parameter></paramdef>
  </funcprototype>
</funcsynopsis>



<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>vendor</parameter></term>
    <listitem><para>A string specifying the session manager vendor.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>release</parameter></term>
    <listitem><para>A string specifying the session manager release number.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>new_client_proc</parameter></term>
    <listitem><para>Callback to be invoked each time a new client connects to the session manager.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>When the <function>SmsNewClientProc</function> callback is invoked, this pointer to manager data will be passed.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>host_based_auth_proc</parameter></term>
    <listitem><para>Host based authentication callback.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>error_length</parameter></term>
    <listitem><para>Length of the <parameter>error_string_ret</parameter> argument passed in.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>error_string_ret</parameter></term>
    <listitem><para>
Returns a null-terminated error message, if any.
The <parameter>error_string_ret</parameter> points to user supplied memory.
No more than <parameter>error_length</parameter> bytes are used.
    </para></listitem>
  </varlistentry>
</variablelist>

    <para>
After the <function>SmsInitialize</function> function is called, the
session manager should call the <function>IceListenForConnections</function>
function to listen for new connections.  Afterwards, each time a
client connects, the session manager should
call <function>IceAcceptConnection</function>
    </para>

    <para>
See <link linkend='authentication_of_clients'>section 9,
&ldquo;Authentication of Clients,&rdquo;</link> for more details on
authentication (including host based authentication).  Also see
the <citetitle pubwork='article'>Inter-Client Exchange
Library</citetitle> standard for further details on listening for and
accepting ICE connections.
    </para>

    <para>
Each time a new client connects to the session manager,
the <function>SmsNewClientProc</function> callback is invoked.  The
session manager obtains a new opaque connection object that it should
use for all future interaction with the client.  At this time, the
session manager must also register a set of callbacks to respond to
the different messages that the client might send.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef Status (*<function>SmsNewClientProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>unsigned long *<parameter>mask_ret</parameter></paramdef>
      <paramdef>SmsCallbacks *<parameter>callbacks_ret</parameter></paramdef>
      <paramdef>char **<parameter>failure_reason_ret</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>A new opaque connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>mask_ret</parameter></term>
    <listitem><para>On return, indicates which callbacks were set by the session manager.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>callbacks_ret</parameter></term>
    <listitem><para>On return, contains the callbacks registered by the session manager.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>failure_reason_ret</parameter></term>
    <listitem><para>Failure reason returned.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
If a failure occurs, the <function>SmsNewClientProc</function> should
return a zero status as well as allocate and return a failure reason
string in <parameter>failure_reason_ret</parameter>.
SMlib will be responsible for freeing this memory.
    </para>

    <para>
The session manager must register a set of callbacks to respond to
client events.  The <parameter>mask_ret</parameter> argument specifies
which callbacks are set.  All of the callbacks specified in this version of
SMlib are mandatory.  The <parameter>mask_ret</parameter> argument is
necessary in order to maintain backwards compatibility in future versions
of the library.
    </para>

    <para>
The following values may be ORed together to obtain a mask value:

      <simplelist type='vert'>
	<member><constant>SmsRegisterClientProcMask</constant></member>
	<member><constant>SmsInteractRequestProcMask</constant></member>
	<member><constant>SmsInteractDoneProcMask</constant></member>
	<member><constant>SmsSaveYourselfRequestProcMask</constant></member>
	<member><constant>SmsSaveYourselfP2RequestProcMask</constant></member>
	<member><constant>SmsSaveYourselfDoneProcMask</constant></member>
	<member><constant>SmsCloseConnectionProcMask</constant></member>
	<member><constant>SmsSetPropertiesProcMask</constant></member>
	<member><constant>SmsDeletePropertiesProcMask</constant></member>
	<member><constant>SmsGetPropertiesProcMask</constant></member>
      </simplelist>
    </para>

    <para>
For each callback, the session manager can register a pointer to
manager data specific to that callback.  This pointer will be passed
to the callback when it is invoked by SMlib.
    </para>

<synopsis>
typedef struct {
	struct {
		SmsRegisterClientProc callback;
		SmPointer manager_data;
	} register_client;

	struct {
		SmsInteractRequestProc callback;
		SmPointer manager_data;
	} interact_request;

	struct {
		SmsInteractDoneProc callback;
		SmPointer manager_data;
	} interact_done;

	struct {
		SmsSaveYourselfRequestProc callback;
		SmPointer manager_data;
	} save_yourself_request;

	struct {
		SmsSaveYourselfPhase2RequestProc callback;
		SmPointer manager_data;
	} save_yourself_phase2_request;

	struct {
		SmsSaveYourselfDoneProc callback;
		SmPointer manager_data;
	} save_yourself_done;

	struct {
		SmsCloseConnectionProc callback;
		SmPointer manager_data;
	} close_connection;

	struct {
		SmsSetPropertiesProc callback;
		SmPointer manager_data;
	} set_properties;

	struct {
		SmsDeletePropertiesProc callback;
		SmPointer manager_data;
	} delete_properties;

	struct {
		SmsGetPropertiesProc callback;
		SmPointer manager_data;
	} get_properties;

} SmsCallbacks;
</synopsis>

    <sect2 id='the_register_client_callback'>
      <title>The Register Client Callback</title>

      <para>
The Register Client callback is the first callback that will be
invoked after the client connects to the session manager.  Its type
is <function>SmsRegisterClientProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef Status (*<function>SmsRegisterClientProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>char *<parameter>previous_id</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>previous_id</parameter></term>
    <listitem><para>The client ID from the previous session.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
Before any further interaction takes place with the client, the client
must be registered with the session manager.
      </para>

      <para>
If the client is being restarted from a previous session,
<parameter>previous_id</parameter> will contain a null-terminated string
representing the client ID from the previous session.
Call <function>free</function> on the <parameter>previous_id</parameter>
pointer when it is no longer needed.  If the client is first joining the
session, <parameter>previous_id</parameter> will be <constant>NULL</constant>.
      </para>

      <para>
If <parameter>previous_id</parameter> is invalid, the session manager should
not register the client at this time.  This callback should return a status
of zero, which will cause an error message to be sent to the client.  The
client should re-register with previous_id set to <constant>NULL</constant>.
      </para>

      <para>
Otherwise, the session manager should register the client with a unique
client ID by calling the <function>SmsRegisterClientReply</function>
function (to be discussed shortly), and the
<function>SmsRegisterClientProc</function> callback should return a
status of one.
      </para>
    </sect2>

    <sect2 id='the_interact_request_callback'>
      <title>The Interact Request Callback</title>

      <para>
The Interact Request callback is of
type <function>SmsInteractRequestProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsInteractRequestProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>int <parameter>dialog_type</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>dialog_type</parameter></term>
    <listitem><para>The type of dialog the client wishes to present to the user.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
When a client receives a &ldquo;Save Yourself&rdquo; message with an
<parameter>interact_style</parameter> of
<constant>SmInteractStyleErrors</constant>
or <constant>SmInteractStyleAny</constant> the client may choose to
interact with the user.  Because only one client can interact with the
user at a time, the client must request to interact with the user.
The session manager should keep a queue of all clients wishing to
interact.  It should send an &ldquo;Interact&rdquo; message to one
client at a time and wait for an &ldquo;Interact Done&rdquo; message
before continuing with the next client.
      </para>

      <para>
The <parameter>dialog_type</parameter> argument specifies
either <constant>SmDialogError</constant> indicating that the client
wants to start an error dialog, or <constant>SmDialogNormal</constant>
meaning that the client wishes to start a nonerror dialog.
      </para>

      <para>
If a shutdown is in progress, the user may have the option of
cancelling the shutdown.  If the shutdown is cancelled (specified in
the &ldquo;Interact Done&rdquo; message), the session manager should
send a &ldquo;Shutdown Cancelled&rdquo; message to each client that
requested to interact.
      </para>
    </sect2>

    <sect2 id='the_interact_done_callback'>
      <title>The Interact Done Callback</title>

      <para>
When the client is done interacting with the user,
the <function>SmsInteractDoneProc</function> callback will be invoked.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsInteractDoneProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>Bool <parameter>cancel_shutdown</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>cancel_shutdown</parameter></term>
    <listitem><para>Specifies if the user requests that the entire shutdown be cancelled.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
Note that the shutdown can be cancelled only if the corresponding
&ldquo;Save Yourself&rdquo; specified <constant>True</constant> for
shutdown and <constant>SmInteractStyleErrors</constant>
or <constant>SmInteractStyleAny</constant> for the
<parameter>interact_style</parameter>.
      </para>
    </sect2>


    <sect2 id='the_save_yourself_request_callback'>
      <title>The Save Yourself Request Callback</title>

      <para>
The Save Yourself Request callback is of
type <function>SmsSaveYourselfRequestProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SaveYourselfRequestProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>int <parameter>save_type</parameter></paramdef>
      <paramdef>Bool <parameter>shutdown</parameter></paramdef>
      <paramdef>int <parameter>interact_style</parameter></paramdef>
      <paramdef>Bool <parameter>fast</parameter></paramdef>
      <paramdef>Bool <parameter>global</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>save_type</parameter></term>
    <listitem><para>Specifies the type of information that should be saved.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>shutdown</parameter></term>
    <listitem><para>Specifies if a shutdown is taking place.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>interact_style</parameter></term>
    <listitem><para>The type of interaction allowed with the user.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>fast</parameter></term>
    <listitem><para>If <constant>True</constant> the client should save its state as quickly as possible.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>global</parameter></term>
    <listitem><para>Controls who gets the &ldquo;Save Yourself.&rdquo;</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The Save Yourself Request prompts the session manager to initiate a
checkpoint or shutdown.  For information on the
<parameter>save_type</parameter>, <parameter>shutdown</parameter>,
<parameter>interact_style</parameter>, and <parameter>fast</parameter>
arguments, see <link linkend='sending_a_save_yourself_message'>section 6.3,
&ldquo;Sending a Save Yourself Message.&rdquo;</link>
      </para>

      <para>
If <parameter>global</parameter> is set to <constant>True</constant> then the
resulting &ldquo;Save Yourself&rdquo; should be sent to all applications.
If <parameter>global</parameter> is set to <constant>False</constant> then the
&ldquo;Save Yourself&rdquo; should only be sent to the client that requested it.
      </para>
    </sect2>

    <sect2 id='the_save_yourself_phase_2_request_callback'>
      <title>The Save Yourself Phase 2 Request Callback</title>

      <para>
The Save Yourself Phase 2 Request callback is of
type <function>SmsSaveYourselfPhase2RequestProc</function>
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsSaveYourselfPhase2RequestProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
This request is sent by clients that manage other clients (for
example, window managers, workspace managers, and so on).  Such
managers must make sure that all of the clients that are being managed
are in an idle state so that their state can be saved.
      </para>
    </sect2>

    <sect2 id='the_save_yourself_done_callback'>
      <title>The Save Yourself Done Callback</title>

      <para>
When the client is done saving its state in response to a
&ldquo;Save Yourself&rdquo; message,
the <function>SmsSaveYourselfDoneProc</function> will be invoked.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SaveYourselfDoneProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>Bool <parameter>success</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>success</parameter></term>
    <listitem><para>If <constant>True</constant> the Save Yourself operation was completed successfully.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
Before the &ldquo;Save Yourself Done&rdquo; was sent, the client must
have set each required property at least once since it registered with
the session manager.
      </para>
    </sect2>

    <sect2 id='the_connection_closed_callback'>
      <title>The Connection Closed Callback</title>

      <para>
If the client properly terminates (that is, it
calls <function>SmcCloseConnection</function>,
the <function>SmsCloseConnectionProc</function> callback is invoked.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsCloseConnectionProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>int <parameter>count</parameter></paramdef>
      <paramdef>char **<parameter>reason_msgs</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
<varlistentry>
  <term><parameter>manager_data</parameter></term>
  <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>count</parameter></term>
    <listitem><para>The number of reason messages.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>reason_msgs</parameter></term>
    <listitem><para>The reasons for closing the connection.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The <parameter>reason_msgs</parameter> argument will most likely
be <constant>NULL</constant> and the <parameter>count</parameter>
argument zero (0) if resignation is expected by the user.  Otherwise,
it contains a list of null-terminated Compound Text strings
representing the reason for termination.  The session manager should
display these reason messages to the user.
      </para>

      <para>
Call <function>SmFreeReasons</function> to free the reason messages.
For further information, see
<link linkend='freeing_data'>section 8, &ldquo;Freeing Data&rdquo;</link>
      </para>
    </sect2>

    <sect2 id='the_set_properties_callback'>
      <title>The Set Properties Callback</title>

      <para>
When the client sets session management properties,
the <function>SmsSetPropertiesProc</function> callback will be invoked.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsSetPropertiesProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>SmProp **<parameter>props</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>props</parameter></term>
    <listitem><para>The list of properties to set.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The properties are specified as an array of property pointers.  For a
description of session management properties and
the <structname>SmProp</structname> structure,
see <link linkend='session_management_properties'>section 7,
&ldquo;Session Management Properties.&rdquo;</link>
      </para>

      <para>
Previously set property values may be over-written.  Some properties
have predefined semantics.  The session manager is required to store
nonpredefined properties.
      </para>

      <para>
To free each property, use <function>SmFreeProperty</function>.
For further information, see <link linkend='freeing_data'>section 8,
&ldquo;Freeing Data&rdquo;</link> You should free the actual array of
pointers with a call to <function>free</function>
      </para>
    </sect2>

    <sect2 id='the_delete_properties_callback'>
      <title>The Delete Properties Callback</title>

      <para>
When the client deletes session management properties,
the <function>SmsDeletePropertiesProc</function> callback will be invoked.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsDeletePropertiesProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>char **<parameter>prop_names</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>prop_names</parameter></term>
    <listitem><para>The list of properties to delete.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The properties are specified as an array of strings.  For a
description of session management properties and
the <structname>SmProp</structname> structure,
see <link linkend='session_management_properties'>section 7,
&ldquo;Session Management Properties.&rdquo;</link>
      </para>
    </sect2>

    <sect2 id='the_get_properties_callback'>
      <title>The Get Properties Callback</title>

      <para>
The <function>SmsGetPropertiesProc</function> callback is invoked when
the client wants to retrieve properties it set.
      </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsGetPropertiesProc</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>SmPointer <parameter>manager_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>manager_data</parameter></term>
    <listitem><para>Manager data specified when the callback was registered.</para></listitem>
  </varlistentry>
</variablelist>

      <para>
The session manager should respond by
calling <function>SmsReturnProperties</function>.
All of the properties set for this client should be returned.
      </para>
    </sect2>
  </sect1>

  <sect1 id='registering_the_client'>
    <title>Registering the Client</title>

    <para>
To register a client (in response to
a <function>SmsRegisterClientProc</function> callback),
use <function>SmsRegisterClientReply</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>Status <function>SmsRegisterClientReply</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>char *<parameter>client_id</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_id</parameter></term>
    <listitem><para>A null-terminated string representing a unique client ID.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The return value of <function>SmsRegisterClientReply</function> is
zero for failure and a positive value for success.  Failure will occur
if SMlib can not allocate memory to hold a copy of the client ID for
it's own internal needs.
    </para>

    <para>
If a non-<constant>NULL</constant> <parameter>previous_id</parameter> was
specified when the client registered itself, <parameter>client_id</parameter>
should be identical to <parameter>previous_id</parameter>.
    </para>

    <para>
Otherwise, <parameter>client_id</parameter> should be a unique ID freshly
generated by the session manager.  In addition, the session manager should
send a &ldquo;Save Yourself&rdquo; message with
<parameter>type</parameter> = <constant>Local</constant>,
<parameter>shutdown</parameter> = <constant>False</constant>,
<parameter>interact-style</parameter> = <constant>None</constant>,
and <parameter>fast</parameter> = <constant>False</constant>
immediately after registering the client.
    </para>

    <para>
Note that once a client ID has been assigned to the client, the client
keeps this ID indefinitely.  If the client is terminated and
restarted, it will be reassigned the same ID.  It is desirable to be
able to pass client IDs around from machine to machine, from user to
user, and from session manager to session manager, while retaining the
identity of the client.  This, combined with the indefinite
persistence of client IDs, means that client IDs need to be globally
unique.
    </para>

    <para>
You should call the <function>SmsGenerateClientID</function> function
to generate a globally unique client ID.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmsGenerateClientID</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>


    <para>
<constant>NULL</constant> will be returned if the ID could not be generated.
Otherwise, the return value of the function is the client ID.
It should be freed with a call to <function>free</function> when
no longer needed.
    </para>
  </sect1>

  <sect1 id='sending_a_save_yourself_message'>
    <title>Sending a Save Yourself Message</title>

    <para>
To send a &ldquo;Save Yourself&rdquo; to a client,
use <function>SmsSaveYourself</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsSaveYourself</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>int <parameter>save_type</parameter></paramdef>
      <paramdef>Bool <parameter>shutdown</parameter></paramdef>
      <paramdef>int <parameter>interact_style</parameter></paramdef>
      <paramdef>Bool <parameter>fast</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>save_type</parameter></term>
    <listitem><para>Specifies the type of information that should be saved.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>shutdown</parameter></term>
    <listitem><para>Specifies if a shutdown is taking place.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>interact_style</parameter></term>
    <listitem><para>The type of interaction allowed with the user.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>fast</parameter></term>
    <listitem><para>If <constant>True</constant> the client should save its state as quickly as possible.</para></listitem>
  </varlistentry>
</variablelist>


    <para>
The session manager sends a &ldquo;Save Yourself&rdquo; message to a
client either to checkpoint it or just before termination so that it
can save its state.  The client responds with zero or more &ldquo;Set
Properties&rdquo; messages to update the properties indicating how to
restart the client.  When all the properties have been set, the client
sends a &ldquo;Save Yourself Done&rdquo; message.
    </para>

    <para>
If <parameter>interact_style</parameter>
is <constant>SmInteractStyleNone</constant> the
client must not interact with the user while saving state.
If <parameter>interact_style</parameter>
is <constant>SmInteractStyleErrors</constant> the
client may interact with the user only if an error condition arises.
If <parameter>interact_style</parameter>
is <constant>SmInteractStyleAny</constant> then the
client may interact with the user for any purpose.  The client must
send an &ldquo;Interact Request&rdquo; message and wait for an
&ldquo;Interact&rdquo; message from the session manager before it can
interact with the user.  When the client is done interacting with the
user, it should send an &ldquo;Interact Done&rdquo; message.  The
&ldquo;Interact Request&rdquo; message can be sent any time after a
&ldquo;Save Yourself&rdquo; and before a &ldquo;Save Yourself
Done.&rdquo;
    </para>

    <para>
If <parameter>save_type</parameter> is <constant>SmSaveLocal</constant>
the client must update the properties to reflect its current state.
Specifically, it should save enough information to restore the state as
seen by the user of this client.  It should not affect the state as seen
by other users.
If <parameter>save_type</parameter> is <constant>SmSaveGlobal</constant>
the user wants the client to commit all of its data to permanent, globally
accessible storage.
If <parameter>save_type</parameter> is <constant>SmSaveBoth</constant>
the client should do both of these (it should first commit the data to
permanent storage before updating its properties).
    </para>

    <para>
The <parameter>shutdown</parameter> argument specifies whether the session
is being shut down.  The interaction is different depending on whether or not
shutdown is set.  If not shutting down, then the client can save and
resume normal operation.  If shutting down, the client must save and
then must prevent interaction until it receives either a
&ldquo;Die&rdquo; or a &ldquo;Shutdown Cancelled,&rdquo; because
anything the user does after the save will be lost.
    </para>

    <para>
The <parameter>fast</parameter> argument specifies that the client should
save its state as quickly as possible.  For example, if the session manager
knows that power is about to fail, it should set <parameter>fast</parameter>
to <constant>True</constant>.
    </para>
  </sect1>

  <sect1 id='sending_a_save_yourself_phase_2_message'>
    <title>Sending a Save Yourself Phase 2 Message</title>

    <para>
In order to send a &ldquo;Save Yourself Phase 2&rdquo; message to a
client, use <function>SmsSaveYourselfPhase2</function>
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsSaveYourselfPhase2</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The session manager sends this message to a client that has previously
sent a &ldquo;Save Yourself Phase 2 Request&rdquo; message.  This
message informs the client that all other clients are in a fixed state
and this client can save state that is associated with other clients.
    </para>
  </sect1>

  <sect1 id='sending_an_interact_message'>
    <title>Sending an Interact Message</title>

    <para>
To send an &ldquo;Interact&rdquo; message to a client,
use <function>SmsInteract</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsInteract</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The &ldquo;Interact&rdquo; message grants the client the privilege of
interacting with the user.  When the client is done interacting with
the user, it must send an &ldquo;Interact Done&rdquo; message to the
session manager.
    </para>
  </sect1>

  <sect1 id='sending_a_save_complete_message'>
    <title>Sending a Save Complete Message</title>

    <para>
To send a &ldquo;Save Complete&rdquo; message to a client,
use <function>SmsSaveComplete</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsSaveComplete</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The session manager sends this message when it is done with a
checkpoint.  The client is then free to change its state.
    </para>
  </sect1>

  <sect1 id='sending_a_die_message'>
    <title>Sending a Die Message</title>

    <para>
To send a &ldquo;Die&rdquo; message to a client,
use <function>SmsDie</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsDie</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
Before the session manager terminates, it should wait for a
&ldquo;Connection Closed&rdquo; message from each client that it sent
a &ldquo;Die&rdquo; message to, timing out appropriately.
    </para>
  </sect1>

  <sect1 id='cancelling_a_shutdown'>
    <title>Cancelling a Shutdown</title>

    <para>
To cancel a shutdown, use <function>SmsShutdownCancelled</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsShutdownCancelled</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The client can now continue as if the shutdown had never happened.  If
the client has not sent a &ldquo;Save Yourself Done&rdquo; message
yet, it can either abort the save and send a &ldquo;Save Yourself
Done&rdquo; with the success argument set to <constant>False</constant>
or it can continue with the save and send a &ldquo;Save Yourself Done&rdquo;
with the <parameter>success</parameter> argument set to reflect the outcome
of the save.
    </para>
  </sect1>
<!-- aaaaaaaaaaaaaaaaa -->

  <sect1 id='returning_properties'>
    <title>Returning Properties</title>

    <para>
In response to a &ldquo;Get Properties&rdquo; message, the session
manager should call <function>SmsReturnProperties</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsReturnProperties</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>int <parameter>num_props</parameter></paramdef>
      <paramdef>SmProp **<parameter>props</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>num_props</parameter></term>
    <listitem><para>The number of properties.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>props</parameter></term>
    <listitem><para>The list of properties to return to the client.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
The properties are returned as an array of property pointers.  For a
description of session management properties and
the <structname>SmProp</structname> structure,
see <link linkend='session_management_properties'>section 7,
&ldquo;Session Management Properties.&rdquo;</link>
    </para>
  </sect1>

  <sect1 id='pinging_a_client'>
    <title>Pinging a Client</title>

    <para>
To check that a client is still alive, you should use
the <function>IcePing</function> function provided by the ICE library.
To do so, the ICE connection must be obtained using
the <function>SmsGetIceConnection</function>
(see <link linkend='using_sms_informational_functions'>section 6.12,
&ldquo;Using Sms Informational Functions&rdquo;</link>).
    </para>


<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>IcePing</function></funcdef>
      <paramdef>IceConn <parameter>ice_conn</parameter></paramdef>
      <paramdef>IcePingReplyProc <parameter>ping_reply_proc</parameter></paramdef>
      <paramdef>IcePointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>ice_conn</parameter></term>
    <listitem><para>A valid ICE connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>ping_reply_proc</parameter></term>
    <listitem><para>The callback to invoke when the Ping reply arrives.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>This pointer will be passed to the <function>IcePingReplyProc</function> callback.</para></listitem>
  </varlistentry>
</variablelist>


    <para>
When the Ping reply is ready (if ever),
the <function>IcePingReplyProc</function> callback will be invoked.  A
session manager should have some sort of timeout period, after which
it assumes the client has unexpectedly died.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>IcePingReplyProc</function>)</funcdef>
      <paramdef>IceConn <parameter>ice_conn</parameter></paramdef>
      <paramdef>IcePointer <parameter>client_data</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>ice_conn</parameter></term>
    <listitem><para>A valid ICE connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>client_data</parameter></term>
    <listitem><para>The client data specified in the call to <function>IcePing</function></para></listitem>
  </varlistentry>
</variablelist>

  </sect1>

  <sect1 id='cleaning_up_after_a_client_disconnects'>
    <title>Cleaning Up After a Client Disconnects</title>

    <para>
When the session manager receives a &ldquo;Connection Closed&rdquo;
message or otherwise detects that the client aborted the connection,
it should call the <function>SmsCleanUp</function> function in order
to free up the connection object.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmsCleanUp</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
</variablelist>

  </sect1>

  <sect1 id='using_sms_informational_functions'>
    <title>Using Sms Informational Functions</title>

<funcsynopsis>
   <funcprototype>
      <funcdef>int <function>SmsProtocolVersion</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmsProtocolVersion</function> returns the major version of
the session management protocol associated with this session.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>int <function>SmsProtocolRevision</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmsProtocolRevision</function> returns the minor version of
the session management protocol associated with this session.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmsClientID</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmsClientID</function> returns a null-terminated string for
the client ID associated with this connection.  You should
call <function>free</function> on this pointer when the client ID is
no longer needed.
    </para>


    <para>
To obtain the host name of a client,
use <function>SmsClientHostName</function>.
This host name will be needed to restart the client.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>char *<function>SmsClientHostName</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
The string returned is of the form
<parameter>protocol</parameter><literal>/</literal><parameter>hostname</parameter>,
where <parameter>protocol</parameter> is one of
{<literal>tcp</literal>, <literal>decnet</literal>, <literal>local</literal>}.
You should call <function>free</function> on the string returned when
it is no longer needed.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>IceConn <function>SmsGetIceConnection</function></funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
<function>SmsGetIceConnection</function> returns the ICE connection
object associated with this session management connection object.  The
ICE connection object can be used to get some additional information
about the connection.  Some of the more useful functions which can be
used on the IceConn are <function>IceConnectionNumber</function>
and <function>IceLastSequenceNumber</function>.
For further information, see the
<citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
    </para>
  </sect1>

  <sect1 id='error_handling2'>
    <title>Error Handling</title>

    <para>
If the session manager receives an unexpected protocol error from a
client, an error handler is invoked by SMlib.  A default error handler
exists which simply prints the error message (it does not exit).  The
session manager can change this error handler by
calling <function>SmsSetErrorHandler</function>.
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>SmsErrorHandler <function>SmsSetErrorHandler</function></funcdef>
      <paramdef>SmsErrorHandler <parameter>handler</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

    <para>
The error handler.  You should pass <constant>NULL</constant>
to restore the default handler.
    </para>

    <para>
<function>SmsSetErrorHandler</function> returns the previous error handler.
The <function>SmsErrorHandler</function> has the following type:
    </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>typedef void (*<function>SmsErrorHandler</function>)</funcdef>
      <paramdef>SmsConn <parameter>sms_conn</parameter></paramdef>
      <paramdef>Bool <parameter>swap</parameter></paramdef>
      <paramdef>int <parameter>offending_minor_opcode</parameter></paramdef>
      <paramdef>unsigned long <parameter>offending_sequence_num</parameter></paramdef>
      <paramdef>int <parameter>error_class</parameter></paramdef>
      <paramdef>int <parameter>severity</parameter></paramdef>
      <paramdef>IcePointer <parameter>values</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>sms_conn</parameter></term>
    <listitem><para>The session management connection object.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>swap</parameter></term>
    <listitem><para>A flag which indicates if the specified values need byte swapping.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>offending_minor_opcode</parameter></term>
    <listitem><para>The minor opcode of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>offending_sequence_num</parameter></term>
    <listitem><para>The sequence number of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>error_class</parameter></term>
    <listitem><para>The error class of the offending message.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>severity</parameter></term>
    <listitem><para>
	<constant>IceCanContinue</constant>,
	<constant>IceFatalToProtocol</constant>, or
	<constant>IceFatalToConnection</constant>
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>values</parameter></term>
    <listitem><para>Any additional error values specific to the minor opcode and class.</para></listitem>
  </varlistentry>
</variablelist>

    <para>
Note that this error handler is invoked for protocol related errors.
To install an error handler to be invoked when an IO error occurs,
use <function>IceSetIOErrorHandler</function>.
For further information, see the
<citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
    </para>
  </sect1>
</chapter>

<chapter id='session_management_properties'>
  <title>Session Management Properties</title>

  <para>
Each property is defined by the <structname>SmProp</structname> structure:

<synopsis>
typedef struct {
	char *name;	/* name of property */
	char *type;	/* type of property */
	int num_vals;	/* number of values */
	SmPropValue *vals;	/* the list of values */
} SmProp;

typedef struct {
	int length;	/* the length of the value */
	SmPointer value;	/* the value */
} SmPropValue;
</synopsis>
  </para>

  <para>
The X Session Management Protocol defines a list of predefined
properties, several of which are required to be set by the client.
The following table specifies the predefined properties and indicates
which ones are required.  Each property has a type associated with it.
  </para>

  <para>
A type of <type>SmCARD8</type> indicates that there is a single 1-byte value.
A type of <type>SmARRAY8</type> indicates that there is a single array of bytes.
A type of <type>SmLISTofARRAY8</type> indicates that there is a list of array of
bytes.
  </para>

<informaltable pgwide='0' frame='none'>
  <tgroup cols='4' align='center'>
    <colspec colname='c1'/>
    <colspec colname='c2'/>
    <colspec colname='c3'/>
    <colspec colname='c4'/>
    <thead>
      <row>
        <entry align='left'>Name</entry>
        <entry align='left'>Type</entry>
        <entry align='left'><acronym>POSIX</acronym> Type</entry>
        <entry align='center'>Required</entry>
      </row>
    </thead>
    <tbody>
      <row>
        <entry align='left'><property>SmCloneCommand</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>Yes</entry>
      </row>
      <row>
        <entry align='left'><property>SmCurrentDirectory</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmARRAY8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmDiscardCommand</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>No*</entry>
      </row>
      <row>
        <entry align='left'><property>SmEnvironment</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmProcessID</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmARRAY8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmProgram</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmARRAY8</type></entry>
        <entry align='center'>Yes</entry>
      </row>
      <row>
        <entry align='left'><property>SmRestartCommand</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>Yes</entry>
      </row>
      <row>
        <entry align='left'><property>SmResignCommand</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmRestartStyleHint</property></entry>
        <entry align='left'><type>SmCARD8</type></entry>
        <entry align='left'><type>SmCARD8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmShutdownCommand</property></entry>
        <entry align='left'>OS-specific</entry>
        <entry align='left'><type>SmLISTofARRAY8</type></entry>
        <entry align='center'>No</entry>
      </row>
      <row>
        <entry align='left'><property>SmUserID</property></entry>
        <entry align='left'><type>SmARRAY8</type></entry>
        <entry align='left'><type>SmARRAY8</type></entry>
        <entry align='center'>Yes</entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>

  <para>
* Required if any state is stored in an external repository (for
example, state file).
  </para>

  <itemizedlist mark='bullet'>
    <listitem><para><property>SmCloneCommand</property></para>
      <para>
This is like the <property>SmRestartCommand</property>, except it restarts a
copy of the application.  The only difference is that the application does not
supply its client ID at register time.  On <acronym>POSIX</acronym> systems,
this should be of type <type>SmLISTofARRAY8</type>.
    </para></listitem>
    <listitem><para><property>SmCurrentDirectory</property></para>
      <para>
On <acronym>POSIX</acronym>-based systems, this specifies the value of the
current directory that needs to be set up prior to starting the
<property>SmProgram</property> and should of type <type>SmARRAY8</type>.
    </para></listitem>
    <listitem><para><property>SmDiscardCommand</property></para>
      <para>
The discard command contains a command that when delivered to the host
that the client is running on (determined from the connection), will
cause it to discard any information about the current state.  If this
command is not specified, the Session Manager will assume that all of
the client's state is encoded in the <property>SmRestartCommand</property>.
On <acronym>POSIX</acronym> systems, the type should be
<type>SmLISTofARRAY8</type>.
    </para></listitem>
    <listitem><para><property>SmEnvironment</property></para>
      <para>
On <acronym>POSIX</acronym> based systems, this will be of type
<type>SmLISTofARRAY8</type>, where the <type>ARRAY8</type>s alternate between
environment variable name and environment variable value.
    </para></listitem>
    <listitem><para><property>SmProcessID</property></para>
      <para>
This specifies an OS-specific identifier for the process.
On <acronym>POSIX</acronym> systems, this should contain the return value
of <function>getpid</function> turned into a Latin-1 (decimal) string.
    </para></listitem>
    <listitem><para><property>SmProgram</property></para>
      <para>
This is the name of the program that is running.  On <acronym>POSIX</acronym>
systems, this should be first parameter passed to <function>execve</function>
and should be of type <type>SmARRAY8</type>.
    </para></listitem>
    <listitem><para><property>SmRestartCommand</property></para>
      <para>
The restart command contains a command that, when delivered to the
host that the client is running on (determined from the connection),
will cause the client to restart in its current state.
On <acronym>POSIX</acronym>-based systems, this is of
type <type>SmLISTofARRAY8</type>, and each of the elements in
the array represents an element in the <varname>argv</varname>
array.  This restart command should ensure that the client restarts
with the specified client-ID.
    </para></listitem>
    <listitem><para><property>SmResignCommand</property></para>
      <para>
A client that sets the <property>SmRestartStyleHint</property>
to <constant>SmRestartAnyway</constant> uses this property to specify a
command that undoes the effect of the client and removes any saved state.
As an example, consider a user that runs <command>xmodmap</command> which
registers with the Session Manager,
sets <property>SmRestartStyleHint</property>
to <constant>SmRestartAnyway</constant>, and then
terminates.  To allow the Session Manager (at the user's request) to
undo this, <command>xmodmap</command> would register a
<property>SmResignCommand</property> that undoes the effects of
the <command>xmodmap</command>.
    </para></listitem>
    <listitem><para><property>SmRestartStyleHint</property></para>
      <para>
If the <property>SmRestartStyleHint</property> is present, it will contain the
style of restarting the client prefers.  If this style is not specified,
<constant>SmRestartIfRunning</constant> is assumed.
The possible values are as follows:

<informaltable pgwide='0' frame='none'>
  <tgroup cols='2' align='center'>
    <colspec colname='c1'/>
    <colspec colname='c2'/>
    <thead>
      <row>
        <entry align='left'>Name</entry>
        <entry align='right'>Value</entry>
      </row>
    </thead>
    <tbody>
      <row>
        <entry align='left'><constant>SmRestartIfRunning</constant></entry>
        <entry align='right'>0</entry>
      </row>
      <row>
        <entry align='left'><constant>SmRestartAnyway</constant></entry>
        <entry align='right'>1</entry>
      </row>
      <row>
        <entry align='left'><constant>SmRestartImmediately</constant></entry>
        <entry align='right'>2</entry>
      </row>
      <row>
        <entry align='left'><constant>SmRestartNever</constant></entry>
        <entry align='right'>3</entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>
      </para>

      <para>
The <constant>SmRestartIfRunning</constant> style is used in the usual case.
The client should be restarted in the next session if it was running at
the end of the current session.
      </para>

      <para>
The <constant>SmRestartAnyway</constant> style is used to tell the Session
Manager that the application should be restarted in the next session even if
it exits before the current session is terminated.  It should be noted that
this is only a hint and the Session Manager will follow the policies
specified by its users in determining what applications to restart.
      </para>

      <para>
A client that uses <constant>SmRestartAnyway</constant> should also set the
<property>SmResignCommand</property> and <property>SmShutdownCommand</property>
properties to commands that undo the state of the client after it exits.
      </para>

      <para>
The SmRestartImmediately style is like SmRestartAnyway, but, in addition, the client is meant to run continuously.  If the client exits, the Session Manager should try to restart it in the current session.
      </para>

      <para>
<constant>SmRestartNever</constant> style specifies that the client does not
wish to be restarted in the next session.
      </para>
    </listitem>
    <listitem><para><property>SmShutdownCommand</property></para>
      <para>
This command is executed at shutdown time to clean up after a client
that is no longer running but retained its state by setting
<property>SmRestartStyleHint</property> to
<constant>SmRestartAnyway</constant>.  The client must not remove any saved
state as the client is still part of the session.  As an
example, consider a client that turns on a camera at start up time.
This client then exits.  At session shutdown, the user wants the
camera turned off.  This client would set the
<property>SmRestartStyleHint</property> to
<constant>SmRestartAnyway</constant> and would register
a <property>SmShutdownCommand</property> that would turn off the camera.
    </para></listitem>
    <listitem><para><property>SmUserID</property></para>
      <para>
Specifies the user ID.  On <acronym>POSIX</acronym>-based systems, this will
contain the user's name (the <structfield>pw_name</structfield> member of
<structname>struct passwd</structname>).
    </para></listitem>
  </itemizedlist>
</chapter>

<chapter id='freeing_data'>
  <title>Freeing Data</title>

  <para>
To free an individual property, use <function>SmFreeProperty</function>
  </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmFreeProperty</function></funcdef>
      <paramdef>SmProp *<parameter>prop</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>prop</parameter></term>
    <listitem><para>The property to free.</para></listitem>
  </varlistentry>
</variablelist>

  <para>
To free the reason strings from
the <function>SmsCloseConnectionProc</function> callback,
use <function>SmFreeReasons</function>
  </para>

<funcsynopsis>
   <funcprototype>
      <funcdef>void <function>SmFreeReasons</function></funcdef>
      <paramdef>int <parameter>count</parameter></paramdef>
      <paramdef>char **<parameter>reasons</parameter></paramdef>
  </funcprototype>
</funcsynopsis>

<variablelist remap='IP'>
  <varlistentry>
    <term><parameter>count</parameter></term>
    <listitem><para>The number of reason strings.</para></listitem>
  </varlistentry>
  <varlistentry>
    <term><parameter>reasons</parameter></term>
    <listitem><para>The list of reason strings to free.</para></listitem>
  </varlistentry>
</variablelist>
</chapter>

<chapter id='authentication_of_clients'>
  <title>Authentication of Clients</title>

  <para>
As stated earlier, the session management protocol is layered on top
of ICE.  Authentication occurs at two levels in the ICE protocol:

<itemizedlist mark='bullet'>
    <listitem><para>The first is when an ICE connection is opened.</para></listitem>
    <listitem><para>The second is when a Protocol Setup occurs on an ICE connection.</para></listitem>
</itemizedlist>
  </para>

  <para>
The authentication methods that are available are
implementation-dependent (that is., dependent on the ICElib and SMlib
implementations in use).  For further information, see the
<citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
  </para>
</chapter>

<chapter id='working_in_a_multithreaded_environment'>
  <title>Working in a Multi-Threaded Environment</title>

  <para>
To declare that multiple threads in an application will be using SMlib
(or any other library layered on top of ICElib), you should
call <function>IceInitThreads</function>.
For further information, see the
<citetitle pubwork='article'>Inter-Client Exchange Library</citetitle>
standard.
  </para>
</chapter>

<chapter id='acknowledgements'>
  <title>Acknowledgements</title>

  <para>
Thanks to the following people for their participation in the
X Session Management design: Jordan Brown, Ellis Cohen, Donna Converse,
Stephen Gildea, Vania Joloboff, Stuart Marks, Bob Scheifler, Ralph Swick,
and Mike Wexler.
  </para>

</chapter>
</book>