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      1 /* yarn.h -- generic interface for thread operations
      2  * Copyright (C) 2008, 2011 Mark Adler
      3  * Version 1.3  13 Jan 2012  Mark Adler
      4  */
      5 
      6 /*
      7   This software is provided 'as-is', without any express or implied
      8   warranty.  In no event will the author be held liable for any damages
      9   arising from the use of this software.
     10 
     11   Permission is granted to anyone to use this software for any purpose,
     12   including commercial applications, and to alter it and redistribute it
     13   freely, subject to the following restrictions:
     14 
     15   1. The origin of this software must not be misrepresented; you must not
     16      claim that you wrote the original software. If you use this software
     17      in a product, an acknowledgment in the product documentation would be
     18      appreciated but is not required.
     19   2. Altered source versions must be plainly marked as such, and must not be
     20      misrepresented as being the original software.
     21   3. This notice may not be removed or altered from any source distribution.
     22 
     23   Mark Adler
     24   madler (at) alumni.caltech.edu
     25  */
     26 
     27 /* Basic thread operations
     28 
     29    This interface isolates the local operating system implementation of threads
     30    from the application in order to facilitate platform independent use of
     31    threads.  All of the implementation details are deliberately hidden.
     32 
     33    Assuming adequate system resources and proper use, none of these functions
     34    can fail.  As a result, any errors encountered will cause an exit() to be
     35    executed.
     36 
     37    These functions allow the simple launching and joining of threads, and the
     38    locking of objects and synchronization of changes of objects.  The latter is
     39    implemented with a single lock type that contains an integer value.  The
     40    value can be ignored for simple exclusive access to an object, or the value
     41    can be used to signal and wait for changes to an object.
     42 
     43    -- Arguments --
     44 
     45    thread *thread;          identifier for launched thread, used by join
     46    void probe(void *);      pointer to function "probe", run when thread starts
     47    void *payload;           single argument passed to the probe function
     48    lock *lock;              a lock with a value -- used for exclusive access to
     49                             an object and to synchronize threads waiting for
     50                             changes to an object
     51    long val;                value to set lock, increment lock, or wait for
     52    int n;                   number of threads joined
     53 
     54    -- Thread functions --
     55 
     56    thread = launch(probe, payload) - launch a thread -- exit via probe() return
     57    join(thread) - join a thread and by joining end it, waiting for the thread
     58         to exit if it hasn't already -- will free the resources allocated by
     59         launch() (don't try to join the same thread more than once)
     60    n = join_all() - join all threads launched by launch() that are not joined
     61         yet and free the resources allocated by the launches, usually to clean
     62         up when the thread processing is done -- join_all() returns an int with
     63         the count of the number of threads joined (join_all() should only be
     64         called from the main thread, and should only be called after any calls
     65         of join() have completed)
     66    destruct(thread) - terminate the thread in mid-execution and join it
     67         (depending on the implementation, the termination may not be immediate,
     68         but may wait for the thread to execute certain thread or file i/o
     69         operations)
     70 
     71    -- Lock functions --
     72 
     73    lock = new_lock(val) - create a new lock with initial value val (lock is
     74         created in the released state)
     75    possess(lock) - acquire exclusive possession of a lock, waiting if necessary
     76    twist(lock, [TO | BY], val) - set lock to or increment lock by val, signal
     77         all threads waiting on this lock and then release the lock -- must
     78         possess the lock before calling (twist releases, so don't do a
     79         release() after a twist() on the same lock)
     80    wait_for(lock, [TO_BE | NOT_TO_BE | TO_BE_MORE_THAN | TO_BE_LESS_THAN], val)
     81         - wait on lock value to be, not to be, be greater than, or be less than
     82         val -- must possess the lock before calling, will possess the lock on
     83         return but the lock is released while waiting to permit other threads
     84         to use twist() to change the value and signal the change (so make sure
     85         that the object is in a usable state when waiting)
     86    release(lock) - release a possessed lock (do not try to release a lock that
     87         the current thread does not possess)
     88    val = peek_lock(lock) - return the value of the lock (assumes that lock is
     89         already possessed, no possess or release is done by peek_lock())
     90    free_lock(lock) - free the resources allocated by new_lock() (application
     91         must assure that the lock is released before calling free_lock())
     92 
     93    -- Memory allocation ---
     94 
     95    yarn_mem(better_malloc, better_free) - set the memory allocation and free
     96         routines for use by the yarn routines where the supplied routines have
     97         the same interface and operation as malloc() and free(), and may be
     98         provided in order to supply thread-safe memory allocation routines or
     99         for any other reason -- by default malloc() and free() will be used
    100 
    101    -- Error control --
    102 
    103    yarn_prefix - a char pointer to a string that will be the prefix for any
    104         error messages that these routines generate before exiting -- if not
    105         changed by the application, "yarn" will be used
    106    yarn_abort - an external function that will be executed when there is an
    107         internal yarn error, due to out of memory or misuse -- this function
    108         may exit to abort the application, or if it returns, the yarn error
    109         handler will exit (set to NULL by default for no action)
    110  */
    111 
    112 extern char *yarn_prefix;
    113 extern void (*yarn_abort)(int);
    114 
    115 void yarn_mem(void *(*)(size_t), void (*)(void *));
    116 
    117 typedef struct thread_s thread;
    118 thread *launch(void (*)(void *), void *);
    119 void join(thread *);
    120 int join_all(void);
    121 void destruct(thread *);
    122 
    123 typedef struct lock_s lock;
    124 lock *new_lock(long);
    125 void possess(lock *);
    126 void release(lock *);
    127 enum twist_op { TO, BY };
    128 void twist(lock *, enum twist_op, long);
    129 enum wait_op {
    130     TO_BE, /* or */ NOT_TO_BE, /* that is the question */
    131     TO_BE_MORE_THAN, TO_BE_LESS_THAN };
    132 void wait_for(lock *, enum wait_op, long);
    133 long peek_lock(lock *);
    134 void free_lock(lock *);
    135