src/mapi/u_current.c

   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
  61 extern void init_glapi_relocs_once(void);
  62 extern 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(USE_ELF_TLS)
 101
 102 __thread struct _glapi_table *u_current_table
 103     __attribute__((tls_model("initial-exec")))
 104     = (struct _glapi_table *) table_noop_array;
 105
 106 __thread void *u_current_context
 107     __attribute__((tls_model("initial-exec")));
 108
 109 #else
 110
 111 struct _glapi_table *u_current_table =
 112    (struct _glapi_table *) table_noop_array;
 113 void *u_current_context;
 114
 115 tss_t u_current_table_tsd;
 116 static tss_t u_current_context_tsd;
 117 static int ThreadSafe;
 118
 119 #endif /* defined(USE_ELF_TLS) */
 120 /*@}*/
 121
 122
 123 void
 124 u_current_destroy(void)
 125 {
 126 #if !defined(USE_ELF_TLS)
 127    tss_delete(u_current_table_tsd);
 128    tss_delete(u_current_context_tsd);
 129 #endif
 130 }
 131
 132
 133 #if !defined(USE_ELF_TLS)
 134
 135 static void
 136 u_current_init_tsd(void)
 137 {
 138    tss_create(&u_current_table_tsd, NULL);
 139    tss_create(&u_current_context_tsd, NULL);
 140 }
 141
 142 /**
 143  * Mutex for multithread check.
 144  */
 145 static mtx_t ThreadCheckMutex = _MTX_INITIALIZER_NP;
 146
 147
 148 #ifdef _WIN32
 149 typedef DWORD thread_id;
 150 #else
 151 typedef thrd_t thread_id;
 152 #endif
 153
 154
 155 static inline thread_id
 156 get_thread_id(void)
 157 {
 158    /*
 159     * XXX: Callers of of this function assume it is a lightweight function.
 160     * But unfortunately C11's thrd_current() gives no such guarantees.  In
 161     * fact, it's pretty hard to have a compliant implementation of
 162     * thrd_current() on Windows with such characteristics.  So for now, we
 163     * side-step this mess and use Windows thread primitives directly here.
 164     */
 165 #ifdef _WIN32
 166    return GetCurrentThreadId();
 167 #else
 168    return thrd_current();
 169 #endif
 170 }
 171
 172
 173 static inline int
 174 thread_id_equal(thread_id t1, thread_id t2)
 175 {
 176 #ifdef _WIN32
 177    return t1 == t2;
 178 #else
 179    return thrd_equal(t1, t2);
 180 #endif
 181 }
 182
 183
 184 /**
 185  * We should call this periodically from a function such as glXMakeCurrent
 186  * in order to test if multiple threads are being used.
 187  */
 188 void
 189 u_current_init(void)
 190 {
 191    static thread_id knownID;
 192    static int firstCall = 1;
 193
 194    if (ThreadSafe)
 195       return;
 196
 197    mtx_lock(&ThreadCheckMutex);
 198    if (firstCall) {
 199       u_current_init_tsd();
 200
 201       knownID = get_thread_id();
 202       firstCall = 0;
 203    }
 204    else if (!thread_id_equal(knownID, get_thread_id())) {
 205       ThreadSafe = 1;
 206       u_current_set_table(NULL);
 207       u_current_set_context(NULL);
 208    }
 209    mtx_unlock(&ThreadCheckMutex);
 210 }
 211
 212 #else
 213
 214 void
 215 u_current_init(void)
 216 {
 217 }
 218
 219 #endif
 220
 221
 222
 223 /**
 224  * Set the current context pointer for this thread.
 225  * The context pointer is an opaque type which should be cast to
 226  * void from the real context pointer type.
 227  */
 228 void
 229 u_current_set_context(const void *ptr)
 230 {
 231    u_current_init();
 232
 233 #if defined(USE_ELF_TLS)
 234    u_current_context = (void *) ptr;
 235 #else
 236    tss_set(u_current_context_tsd, (void *) ptr);
 237    u_current_context = (ThreadSafe) ? NULL : (void *) ptr;
 238 #endif
 239 }
 240
 241 /**
 242  * Get the current context pointer for this thread.
 243  * The context pointer is an opaque type which should be cast from
 244  * void to the real context pointer type.
 245  */
 246 void *
 247 u_current_get_context_internal(void)
 248 {
 249 #if defined(USE_ELF_TLS)
 250    return u_current_context;
 251 #else
 252    return ThreadSafe ? tss_get(u_current_context_tsd) : u_current_context;
 253 #endif
 254 }
 255
 256 /**
 257  * Set the global or per-thread dispatch table pointer.
 258  * If the dispatch parameter is NULL we'll plug in the no-op dispatch
 259  * table (__glapi_noop_table).
 260  */
 261 void
 262 u_current_set_table(const struct _glapi_table *tbl)
 263 {
 264    u_current_init();
 265
 266    stub_init_once();
 267
 268    if (!tbl)
 269       tbl = (const struct _glapi_table *) table_noop_array;
 270
 271 #if defined(USE_ELF_TLS)
 272    u_current_table = (struct _glapi_table *) tbl;
 273 #else
 274    tss_set(u_current_table_tsd, (void *) tbl);
 275    u_current_table = (ThreadSafe) ? NULL : (void *) tbl;
 276 #endif
 277 }
 278
 279 /**
 280  * Return pointer to current dispatch table for calling thread.
 281  */
 282 struct _glapi_table *
 283 u_current_get_table_internal(void)
 284 {
 285 #if defined(USE_ELF_TLS)
 286    return u_current_table;
 287 #else
 288    if (ThreadSafe)
 289       return (struct _glapi_table *) tss_get(u_current_table_tsd);
 290    else
 291       return (struct _glapi_table *) u_current_table;
 292 #endif
 293 }