1/*
2 * Mesa 3-D graphics library
3 *
4 * Copyright (C) 1999-2008  Brian Paul   All Rights Reserved.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the "Software"),
8 * to deal in the Software without restriction, including without limitation
9 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 * and/or sell copies of the Software, and to permit persons to whom the
11 * Software is furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included
14 * in all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
17 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
20 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
21 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
22 * OTHER DEALINGS IN THE SOFTWARE.
23 */
24
25
26/*
27 * This file manages the OpenGL API dispatch layer.
28 * The dispatch table (struct _glapi_table) is basically just a list
29 * of function pointers.
30 * There are functions to set/get the current dispatch table for the
31 * current thread and to manage registration/dispatch of dynamically
32 * added extension functions.
33 *
34 * It's intended that this file and the other glapi*.[ch] files are
35 * flexible enough to be reused in several places:  XFree86, DRI-
36 * based libGL.so, and perhaps the SGI SI.
37 *
38 * NOTE: There are no dependencies on Mesa in this code.
39 *
40 * Versions (API changes):
41 *   2000/02/23  - original version for Mesa 3.3 and XFree86 4.0
42 *   2001/01/16  - added dispatch override feature for Mesa 3.5
43 *   2002/06/28  - added _glapi_set_warning_func(), Mesa 4.1.
44 *   2002/10/01  - _glapi_get_proc_address() will now generate new entrypoints
45 *                 itself (using offset ~0).  _glapi_add_entrypoint() can be
46 *                 called afterward and it'll fill in the correct dispatch
47 *                 offset.  This allows DRI libGL to avoid probing for DRI
48 *                 drivers!  No changes to the public glapi interface.
49 */
50
51#include "c11/threads.h"
52#include "u_current.h"
53
54#ifndef MAPI_MODE_UTIL
55
56#include "table.h"
57#include "stub.h"
58
59#else
60
61extern void init_glapi_relocs_once(void);
62extern void (*__glapi_noop_table[])(void);
63
64#define table_noop_array __glapi_noop_table
65#define stub_init_once() init_glapi_relocs_once()
66
67#endif
68
69/**
70 * \name Current dispatch and current context control variables
71 *
72 * Depending on whether or not multithreading is support, and the type of
73 * support available, several variables are used to store the current context
74 * pointer and the current dispatch table pointer.  In the non-threaded case,
75 * the variables \c _glapi_Dispatch and \c _glapi_Context are used for this
76 * purpose.
77 *
78 * In the "normal" threaded case, the variables \c _glapi_Dispatch and
79 * \c _glapi_Context will be \c NULL if an application is detected as being
80 * multithreaded.  Single-threaded applications will use \c _glapi_Dispatch
81 * and \c _glapi_Context just like the case without any threading support.
82 * When \c _glapi_Dispatch and \c _glapi_Context are \c NULL, the thread state
83 * data \c _gl_DispatchTSD and \c ContextTSD are used.  Drivers and the
84 * static dispatch functions access these variables via \c _glapi_get_dispatch
85 * and \c _glapi_get_context.
86 *
87 * There is a race condition in setting \c _glapi_Dispatch to \c NULL.  It is
88 * possible for the original thread to be setting it at the same instant a new
89 * thread, perhaps running on a different processor, is clearing it.  Because
90 * of that, \c ThreadSafe, which can only ever be changed to \c GL_TRUE, is
91 * used to determine whether or not the application is multithreaded.
92 *
93 * In the TLS case, the variables \c _glapi_Dispatch and \c _glapi_Context are
94 * hardcoded to \c NULL.  Instead the TLS variables \c _glapi_tls_Dispatch and
95 * \c _glapi_tls_Context are used.  Having \c _glapi_Dispatch and
96 * \c _glapi_Context be hardcoded to \c NULL maintains binary compatability
97 * between TLS enabled loaders and non-TLS DRI drivers.
98 */
99/*@{*/
100#if defined(GLX_USE_TLS)
101
102__thread struct _glapi_table *u_current_table
103    __attribute__((tls_model("initial-exec")))
104#if defined(__NetBSD__)
105    = NULL; /* non-zero initializers not supported with dlopen */
106#else
107    = (struct _glapi_table *) table_noop_array;
108#endif
109
110__thread void *u_current_context
111    __attribute__((tls_model("initial-exec")));
112
113#else
114
115struct _glapi_table *u_current_table =
116   (struct _glapi_table *) table_noop_array;
117void *u_current_context;
118
119tss_t u_current_table_tsd;
120static tss_t u_current_context_tsd;
121static int ThreadSafe;
122
123#endif /* defined(GLX_USE_TLS) */
124/*@}*/
125
126
127void
128u_current_destroy(void)
129{
130#if !defined(GLX_USE_TLS)
131   tss_delete(u_current_table_tsd);
132   tss_delete(u_current_context_tsd);
133#endif
134}
135
136
137#if !defined(GLX_USE_TLS)
138
139static void
140u_current_init_tsd(void)
141{
142   tss_create(&u_current_table_tsd, NULL);
143   tss_create(&u_current_context_tsd, NULL);
144}
145
146/**
147 * Mutex for multithread check.
148 */
149static mtx_t ThreadCheckMutex = _MTX_INITIALIZER_NP;
150
151
152#ifdef _WIN32
153typedef DWORD thread_id;
154#else
155typedef thrd_t thread_id;
156#endif
157
158
159static inline thread_id
160get_thread_id(void)
161{
162   /*
163    * XXX: Callers of of this function assume it is a lightweight function.
164    * But unfortunately C11's thrd_current() gives no such guarantees.  In
165    * fact, it's pretty hard to have a compliant implementation of
166    * thrd_current() on Windows with such characteristics.  So for now, we
167    * side-step this mess and use Windows thread primitives directly here.
168    */
169#ifdef _WIN32
170   return GetCurrentThreadId();
171#else
172   return thrd_current();
173#endif
174}
175
176
177static inline int
178thread_id_equal(thread_id t1, thread_id t2)
179{
180#ifdef _WIN32
181   return t1 == t2;
182#else
183   return thrd_equal(t1, t2);
184#endif
185}
186
187
188/**
189 * We should call this periodically from a function such as glXMakeCurrent
190 * in order to test if multiple threads are being used.
191 */
192void
193u_current_init(void)
194{
195   static thread_id knownID;
196   static int firstCall = 1;
197
198   if (ThreadSafe)
199      return;
200
201   mtx_lock(&ThreadCheckMutex);
202   if (firstCall) {
203      u_current_init_tsd();
204
205      knownID = get_thread_id();
206      firstCall = 0;
207   }
208   else if (!thread_id_equal(knownID, get_thread_id())) {
209      ThreadSafe = 1;
210      u_current_set_table(NULL);
211      u_current_set_context(NULL);
212   }
213   mtx_unlock(&ThreadCheckMutex);
214}
215
216#else
217
218void
219u_current_init(void)
220{
221}
222
223#endif
224
225
226
227/**
228 * Set the current context pointer for this thread.
229 * The context pointer is an opaque type which should be cast to
230 * void from the real context pointer type.
231 */
232void
233u_current_set_context(const void *ptr)
234{
235   u_current_init();
236
237#if defined(GLX_USE_TLS)
238   u_current_context = (void *) ptr;
239#else
240   tss_set(u_current_context_tsd, (void *) ptr);
241   u_current_context = (ThreadSafe) ? NULL : (void *) ptr;
242#endif
243}
244
245/**
246 * Get the current context pointer for this thread.
247 * The context pointer is an opaque type which should be cast from
248 * void to the real context pointer type.
249 */
250void *
251u_current_get_context_internal(void)
252{
253#if defined(GLX_USE_TLS)
254   return u_current_context;
255#else
256   return ThreadSafe ? tss_get(u_current_context_tsd) : u_current_context;
257#endif
258}
259
260/**
261 * Set the global or per-thread dispatch table pointer.
262 * If the dispatch parameter is NULL we'll plug in the no-op dispatch
263 * table (__glapi_noop_table).
264 */
265void
266u_current_set_table(const struct _glapi_table *tbl)
267{
268   u_current_init();
269
270   stub_init_once();
271
272   if (!tbl)
273      tbl = (const struct _glapi_table *) table_noop_array;
274
275#if defined(GLX_USE_TLS)
276   u_current_table = (struct _glapi_table *) tbl;
277#else
278   tss_set(u_current_table_tsd, (void *) tbl);
279   u_current_table = (ThreadSafe) ? NULL : (void *) tbl;
280#endif
281}
282
283/**
284 * Return pointer to current dispatch table for calling thread.
285 */
286struct _glapi_table *
287u_current_get_table_internal(void)
288{
289#if defined(GLX_USE_TLS)
290#  if defined(__NetBSD__)
291   return (likely(u_current_table) ? u_current_table : (struct _glapi_table *) table_noop_array);
292#  else
293   return u_current_table;
294#  endif
295#else
296   if (ThreadSafe)
297      return (struct _glapi_table *) tss_get(u_current_table_tsd);
298   else
299      return (struct _glapi_table *) u_current_table;
300#endif
301}
302