src/systhread.c

   1 /* System thread definitions
   2 Copyright (C) 2012-2017 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Emacs.
   5
   6 GNU Emacs is free software: you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation, either version 3 of the License, or
   9 (at your option) any later version.
  10
  11 GNU Emacs is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include <config.h>
  20 #include <setjmp.h>
  21 #include "lisp.h"
  22
  23 #ifndef THREADS_ENABLED
  24
  25 void
  26 sys_mutex_init (sys_mutex_t *m)
  27 {
  28   *m = 0;
  29 }
  30
  31 void
  32 sys_mutex_lock (sys_mutex_t *m)
  33 {
  34 }
  35
  36 void
  37 sys_mutex_unlock (sys_mutex_t *m)
  38 {
  39 }
  40
  41 void
  42 sys_mutex_destroy (sys_mutex_t *m)
  43 {
  44 }
  45
  46 void
  47 sys_cond_init (sys_cond_t *c)
  48 {
  49   *c = 0;
  50 }
  51
  52 void
  53 sys_cond_wait (sys_cond_t *c, sys_mutex_t *m)
  54 {
  55 }
  56
  57 void
  58 sys_cond_signal (sys_cond_t *c)
  59 {
  60 }
  61
  62 void
  63 sys_cond_broadcast (sys_cond_t *c)
  64 {
  65 }
  66
  67 void
  68 sys_cond_destroy (sys_cond_t *c)
  69 {
  70 }
  71
  72 sys_thread_t
  73 sys_thread_self (void)
  74 {
  75   return 0;
  76 }
  77
  78 int
  79 sys_thread_equal (sys_thread_t x, sys_thread_t y)
  80 {
  81   return x == y;
  82 }
  83
  84 int
  85 sys_thread_create (sys_thread_t *t, const char *name,
  86                    thread_creation_function *func, void *datum)
  87 {
  88   return 0;
  89 }
  90
  91 void
  92 sys_thread_yield (void)
  93 {
  94 }
  95
  96 #elif defined (HAVE_PTHREAD)
  97
  98 #include <sched.h>
  99
 100 #ifdef HAVE_SYS_PRCTL_H
 101 #include <sys/prctl.h>
 102 #endif
 103
 104 void
 105 sys_mutex_init (sys_mutex_t *mutex)
 106 {
 107   pthread_mutex_init (mutex, NULL);
 108 }
 109
 110 void
 111 sys_mutex_lock (sys_mutex_t *mutex)
 112 {
 113   pthread_mutex_lock (mutex);
 114 }
 115
 116 void
 117 sys_mutex_unlock (sys_mutex_t *mutex)
 118 {
 119   pthread_mutex_unlock (mutex);
 120 }
 121
 122 void
 123 sys_mutex_destroy (sys_mutex_t *mutex)
 124 {
 125   pthread_mutex_destroy (mutex);
 126 }
 127
 128 void
 129 sys_cond_init (sys_cond_t *cond)
 130 {
 131   pthread_cond_init (cond, NULL);
 132 }
 133
 134 void
 135 sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
 136 {
 137   pthread_cond_wait (cond, mutex);
 138 }
 139
 140 void
 141 sys_cond_signal (sys_cond_t *cond)
 142 {
 143   pthread_cond_signal (cond);
 144 }
 145
 146 void
 147 sys_cond_broadcast (sys_cond_t *cond)
 148 {
 149   pthread_cond_broadcast (cond);
 150 }
 151
 152 void
 153 sys_cond_destroy (sys_cond_t *cond)
 154 {
 155   pthread_cond_destroy (cond);
 156 }
 157
 158 sys_thread_t
 159 sys_thread_self (void)
 160 {
 161   return pthread_self ();
 162 }
 163
 164 int
 165 sys_thread_equal (sys_thread_t one, sys_thread_t two)
 166 {
 167   return pthread_equal (one, two);
 168 }
 169
 170 int
 171 sys_thread_create (sys_thread_t *thread_ptr, const char *name,
 172                    thread_creation_function *func, void *arg)
 173 {
 174   pthread_attr_t attr;
 175   int result = 0;
 176
 177   if (pthread_attr_init (&attr))
 178     return 0;
 179
 180   if (!pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED))
 181     {
 182       result = pthread_create (thread_ptr, &attr, func, arg) == 0;
 183 #if defined (HAVE_SYS_PRCTL_H) && defined (HAVE_PRCTL) && defined (PR_SET_NAME)
 184       if (result && name != NULL)
 185         prctl (PR_SET_NAME, name);
 186 #endif
 187     }
 188
 189   pthread_attr_destroy (&attr);
 190
 191   return result;
 192 }
 193
 194 void
 195 sys_thread_yield (void)
 196 {
 197   sched_yield ();
 198 }
 199
 200 #elif defined (WINDOWSNT)
 201
 202 #include <windows.h>
 203
 204 /* Cannot include <process.h> because of the local header by the same
 205    name, sigh.  */
 206 uintptr_t _beginthread (void (__cdecl *)(void *), unsigned, void *);
 207
 208 /* Mutexes are implemented as critical sections, because they are
 209    faster than Windows mutex objects (implemented in userspace), and
 210    satisfy the requirements, since we only need to synchronize within a
 211    single process.  */
 212 void
 213 sys_mutex_init (sys_mutex_t *mutex)
 214 {
 215   InitializeCriticalSection ((LPCRITICAL_SECTION)mutex);
 216 }
 217
 218 void
 219 sys_mutex_lock (sys_mutex_t *mutex)
 220 {
 221   /* FIXME: What happens if the owning thread exits without releasing
 222      the mutex?  According to MSDN, the result is undefined behavior.  */
 223   EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
 224 }
 225
 226 void
 227 sys_mutex_unlock (sys_mutex_t *mutex)
 228 {
 229   LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
 230 }
 231
 232 void
 233 sys_mutex_destroy (sys_mutex_t *mutex)
 234 {
 235   /* FIXME: According to MSDN, deleting a critical session that is
 236      owned by a thread leaves the other threads waiting for the
 237      critical session in an undefined state.  Posix docs seem to say
 238      the same about pthread_mutex_destroy.  Do we need to protect
 239      against such calamities?  */
 240   DeleteCriticalSection ((LPCRITICAL_SECTION)mutex);
 241 }
 242
 243 void
 244 sys_cond_init (sys_cond_t *cond)
 245 {
 246   cond->initialized = false;
 247   cond->wait_count = 0;
 248   /* Auto-reset event for signal.  */
 249   cond->events[CONDV_SIGNAL] = CreateEvent (NULL, FALSE, FALSE, NULL);
 250   /* Manual-reset event for broadcast.  */
 251   cond->events[CONDV_BROADCAST] = CreateEvent (NULL, TRUE, FALSE, NULL);
 252   if (!cond->events[CONDV_SIGNAL] || !cond->events[CONDV_BROADCAST])
 253     return;
 254   InitializeCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 255   cond->initialized = true;
 256 }
 257
 258 void
 259 sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
 260 {
 261   DWORD wait_result;
 262   bool last_thread_waiting;
 263
 264   if (!cond->initialized)
 265     return;
 266
 267   /* Increment the wait count avoiding race conditions.  */
 268   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 269   cond->wait_count++;
 270   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 271
 272   /* Release the mutex and wait for either the signal or the broadcast
 273      event.  */
 274   LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
 275   wait_result = WaitForMultipleObjects (2, cond->events, FALSE, INFINITE);
 276
 277   /* Decrement the wait count and see if we are the last thread
 278      waiting on the condition variable.  */
 279   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 280   cond->wait_count--;
 281   last_thread_waiting =
 282     wait_result == WAIT_OBJECT_0 + CONDV_BROADCAST
 283     && cond->wait_count == 0;
 284   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 285
 286   /* Broadcast uses a manual-reset event, so when the last thread is
 287      released, we must manually reset that event.  */
 288   if (last_thread_waiting)
 289     ResetEvent (cond->events[CONDV_BROADCAST]);
 290
 291   /* Per the API, re-acquire the mutex.  */
 292   EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
 293 }
 294
 295 void
 296 sys_cond_signal (sys_cond_t *cond)
 297 {
 298   bool threads_waiting;
 299
 300   if (!cond->initialized)
 301     return;
 302
 303   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 304   threads_waiting = cond->wait_count > 0;
 305   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 306
 307   if (threads_waiting)
 308     SetEvent (cond->events[CONDV_SIGNAL]);
 309 }
 310
 311 void
 312 sys_cond_broadcast (sys_cond_t *cond)
 313 {
 314   bool threads_waiting;
 315
 316   if (!cond->initialized)
 317     return;
 318
 319   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 320   threads_waiting = cond->wait_count > 0;
 321   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 322
 323   if (threads_waiting)
 324     SetEvent (cond->events[CONDV_BROADCAST]);
 325 }
 326
 327 void
 328 sys_cond_destroy (sys_cond_t *cond)
 329 {
 330   if (cond->events[CONDV_SIGNAL])
 331     CloseHandle (cond->events[CONDV_SIGNAL]);
 332   if (cond->events[CONDV_BROADCAST])
 333     CloseHandle (cond->events[CONDV_BROADCAST]);
 334
 335   if (!cond->initialized)
 336     return;
 337
 338   /* FIXME: What if wait_count is non-zero, i.e. there are still
 339      threads waiting on this condition variable?  */
 340   DeleteCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 341 }
 342
 343 sys_thread_t
 344 sys_thread_self (void)
 345 {
 346   return (sys_thread_t) GetCurrentThreadId ();
 347 }
 348
 349 int
 350 sys_thread_equal (sys_thread_t one, sys_thread_t two)
 351 {
 352   return one == two;
 353 }
 354
 355 static thread_creation_function *thread_start_address;
 356
 357 /* _beginthread wants a void function, while we are passed a function
 358    that returns a pointer.  So we use a wrapper.  */
 359 static void
 360 w32_beginthread_wrapper (void *arg)
 361 {
 362   (void)thread_start_address (arg);
 363 }
 364
 365 int
 366 sys_thread_create (sys_thread_t *thread_ptr, const char *name,
 367                    thread_creation_function *func, void *arg)
 368 {
 369   /* FIXME: Do threads that run Lisp require some minimum amount of
 370      stack?  Zero here means each thread will get the same amount as
 371      the main program.  On GNU/Linux, it seems like the stack is 2MB
 372      by default, overridden by RLIMIT_STACK at program start time.
 373      Not sure what to do with this.  See also the comment in
 374      w32proc.c:new_child.  */
 375   const unsigned stack_size = 0;
 376   uintptr_t thandle;
 377
 378   thread_start_address = func;
 379
 380   /* We use _beginthread rather than CreateThread because the former
 381      arranges for the thread handle to be automatically closed when
 382      the thread exits, thus preventing handle leaks and/or the need to
 383      track all the threads and close their handles when they exit.
 384      Also, MSDN seems to imply that code which uses CRT _must_ call
 385      _beginthread, although if that is true, we already violate that
 386      rule in many places...  */
 387   thandle = _beginthread (w32_beginthread_wrapper, stack_size, arg);
 388   if (thandle == (uintptr_t)-1L)
 389     return 0;
 390
 391   /* Kludge alert!  We use the Windows thread ID, an unsigned 32-bit
 392      number, as the sys_thread_t type, because that ID is the only
 393      unique identifier of a thread on Windows.  But _beginthread
 394      returns a handle of the thread, and there's no easy way of
 395      getting the thread ID given a handle (GetThreadId is available
 396      only since Vista, so we cannot use it portably).  Fortunately,
 397      the value returned by sys_thread_create is not used by its
 398      callers; instead, run_thread, which runs in the context of the
 399      new thread, calls sys_thread_self and uses its return value;
 400      sys_thread_self in this implementation calls GetCurrentThreadId.
 401      Therefore, we return some more or less arbitrary value of the
 402      thread ID from this function. */
 403   *thread_ptr = thandle & 0xFFFFFFFF;
 404   return 1;
 405 }
 406
 407 void
 408 sys_thread_yield (void)
 409 {
 410   Sleep (0);
 411 }
 412
 413 #else
 414
 415 #error port me
 416
 417 #endif