src/systhread.c

   1 /* System thread definitions
   2 Copyright (C) 2012-2018 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 <https://www.gnu.org/licenses/>.  */
  18
  19 #include <config.h>
  20 #include <setjmp.h>
  21 #include "lisp.h"
  22
  23 #ifdef HAVE_NS
  24 #include "nsterm.h"
  25 #endif
  26
  27 #ifndef THREADS_ENABLED
  28
  29 void
  30 sys_mutex_init (sys_mutex_t *m)
  31 {
  32   *m = 0;
  33 }
  34
  35 void
  36 sys_mutex_lock (sys_mutex_t *m)
  37 {
  38 }
  39
  40 void
  41 sys_mutex_unlock (sys_mutex_t *m)
  42 {
  43 }
  44
  45 void
  46 sys_cond_init (sys_cond_t *c)
  47 {
  48   *c = 0;
  49 }
  50
  51 void
  52 sys_cond_wait (sys_cond_t *c, sys_mutex_t *m)
  53 {
  54 }
  55
  56 void
  57 sys_cond_signal (sys_cond_t *c)
  58 {
  59 }
  60
  61 void
  62 sys_cond_broadcast (sys_cond_t *c)
  63 {
  64 }
  65
  66 void
  67 sys_cond_destroy (sys_cond_t *c)
  68 {
  69 }
  70
  71 sys_thread_t
  72 sys_thread_self (void)
  73 {
  74   return 0;
  75 }
  76
  77 int
  78 sys_thread_create (sys_thread_t *t, const char *name,
  79                    thread_creation_function *func, void *datum)
  80 {
  81   return 0;
  82 }
  83
  84 void
  85 sys_thread_yield (void)
  86 {
  87 }
  88
  89 #elif defined (HAVE_PTHREAD)
  90
  91 #include <sched.h>
  92
  93 #ifdef HAVE_SYS_PRCTL_H
  94 #include <sys/prctl.h>
  95 #endif
  96
  97 void
  98 sys_mutex_init (sys_mutex_t *mutex)
  99 {
 100   pthread_mutex_init (mutex, NULL);
 101 }
 102
 103 void
 104 sys_mutex_lock (sys_mutex_t *mutex)
 105 {
 106   pthread_mutex_lock (mutex);
 107 }
 108
 109 void
 110 sys_mutex_unlock (sys_mutex_t *mutex)
 111 {
 112   pthread_mutex_unlock (mutex);
 113 }
 114
 115 void
 116 sys_cond_init (sys_cond_t *cond)
 117 {
 118   pthread_cond_init (cond, NULL);
 119 }
 120
 121 void
 122 sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
 123 {
 124   pthread_cond_wait (cond, mutex);
 125 }
 126
 127 void
 128 sys_cond_signal (sys_cond_t *cond)
 129 {
 130   pthread_cond_signal (cond);
 131 }
 132
 133 void
 134 sys_cond_broadcast (sys_cond_t *cond)
 135 {
 136   pthread_cond_broadcast (cond);
 137 #ifdef HAVE_NS
 138   /* Send an app defined event to break out of the NS run loop.
 139      It seems that if ns_select is running the NS run loop, this
 140      broadcast has no effect until the loop is done, breaking a couple
 141      of tests in thread-tests.el. */
 142   ns_run_loop_break ();
 143 #endif
 144 }
 145
 146 void
 147 sys_cond_destroy (sys_cond_t *cond)
 148 {
 149   pthread_cond_destroy (cond);
 150 }
 151
 152 sys_thread_t
 153 sys_thread_self (void)
 154 {
 155   return pthread_self ();
 156 }
 157
 158 int
 159 sys_thread_create (sys_thread_t *thread_ptr, const char *name,
 160                    thread_creation_function *func, void *arg)
 161 {
 162   pthread_attr_t attr;
 163   int result = 0;
 164
 165   if (pthread_attr_init (&attr))
 166     return 0;
 167
 168   if (!pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED))
 169     {
 170       result = pthread_create (thread_ptr, &attr, func, arg) == 0;
 171 #if defined (HAVE_SYS_PRCTL_H) && defined (HAVE_PRCTL) && defined (PR_SET_NAME)
 172       if (result && name != NULL)
 173         prctl (PR_SET_NAME, name);
 174 #endif
 175     }
 176
 177   pthread_attr_destroy (&attr);
 178
 179   return result;
 180 }
 181
 182 void
 183 sys_thread_yield (void)
 184 {
 185   sched_yield ();
 186 }
 187
 188 #elif defined (WINDOWSNT)
 189
 190 #include <w32term.h>
 191
 192 /* Cannot include <process.h> because of the local header by the same
 193    name, sigh.  */
 194 uintptr_t _beginthread (void (__cdecl *)(void *), unsigned, void *);
 195
 196 /* Mutexes are implemented as critical sections, because they are
 197    faster than Windows mutex objects (implemented in userspace), and
 198    satisfy the requirements, since we only need to synchronize within a
 199    single process.  */
 200 void
 201 sys_mutex_init (sys_mutex_t *mutex)
 202 {
 203   InitializeCriticalSection ((LPCRITICAL_SECTION)mutex);
 204 }
 205
 206 void
 207 sys_mutex_lock (sys_mutex_t *mutex)
 208 {
 209   /* FIXME: What happens if the owning thread exits without releasing
 210      the mutex?  According to MSDN, the result is undefined behavior.  */
 211   EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
 212 }
 213
 214 void
 215 sys_mutex_unlock (sys_mutex_t *mutex)
 216 {
 217   LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
 218 }
 219
 220 void
 221 sys_cond_init (sys_cond_t *cond)
 222 {
 223   cond->initialized = false;
 224   cond->wait_count = 0;
 225   /* Auto-reset event for signal.  */
 226   cond->events[CONDV_SIGNAL] = CreateEvent (NULL, FALSE, FALSE, NULL);
 227   /* Manual-reset event for broadcast.  */
 228   cond->events[CONDV_BROADCAST] = CreateEvent (NULL, TRUE, FALSE, NULL);
 229   if (!cond->events[CONDV_SIGNAL] || !cond->events[CONDV_BROADCAST])
 230     return;
 231   InitializeCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 232   cond->initialized = true;
 233 }
 234
 235 void
 236 sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
 237 {
 238   DWORD wait_result;
 239   bool last_thread_waiting;
 240
 241   if (!cond->initialized)
 242     return;
 243
 244   /* Increment the wait count avoiding race conditions.  */
 245   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 246   cond->wait_count++;
 247   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 248
 249   /* Release the mutex and wait for either the signal or the broadcast
 250      event.  */
 251   LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
 252   wait_result = WaitForMultipleObjects (2, cond->events, FALSE, INFINITE);
 253
 254   /* Decrement the wait count and see if we are the last thread
 255      waiting on the condition variable.  */
 256   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 257   cond->wait_count--;
 258   last_thread_waiting =
 259     wait_result == WAIT_OBJECT_0 + CONDV_BROADCAST
 260     && cond->wait_count == 0;
 261   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 262
 263   /* Broadcast uses a manual-reset event, so when the last thread is
 264      released, we must manually reset that event.  */
 265   if (last_thread_waiting)
 266     ResetEvent (cond->events[CONDV_BROADCAST]);
 267
 268   /* Per the API, re-acquire the mutex.  */
 269   EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
 270 }
 271
 272 void
 273 sys_cond_signal (sys_cond_t *cond)
 274 {
 275   bool threads_waiting;
 276
 277   if (!cond->initialized)
 278     return;
 279
 280   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 281   threads_waiting = cond->wait_count > 0;
 282   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 283
 284   if (threads_waiting)
 285     SetEvent (cond->events[CONDV_SIGNAL]);
 286 }
 287
 288 void
 289 sys_cond_broadcast (sys_cond_t *cond)
 290 {
 291   bool threads_waiting;
 292
 293   if (!cond->initialized)
 294     return;
 295
 296   EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 297   threads_waiting = cond->wait_count > 0;
 298   LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 299
 300   if (threads_waiting)
 301     SetEvent (cond->events[CONDV_BROADCAST]);
 302 }
 303
 304 void
 305 sys_cond_destroy (sys_cond_t *cond)
 306 {
 307   if (cond->events[CONDV_SIGNAL])
 308     CloseHandle (cond->events[CONDV_SIGNAL]);
 309   if (cond->events[CONDV_BROADCAST])
 310     CloseHandle (cond->events[CONDV_BROADCAST]);
 311
 312   if (!cond->initialized)
 313     return;
 314
 315   /* FIXME: What if wait_count is non-zero, i.e. there are still
 316      threads waiting on this condition variable?  */
 317   DeleteCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
 318 }
 319
 320 sys_thread_t
 321 sys_thread_self (void)
 322 {
 323   return (sys_thread_t) GetCurrentThreadId ();
 324 }
 325
 326 static thread_creation_function *thread_start_address;
 327
 328 /* _beginthread wants a void function, while we are passed a function
 329    that returns a pointer.  So we use a wrapper.  See the command in
 330    w32term.h about the need for ALIGN_STACK attribute.  */
 331 static void ALIGN_STACK
 332 w32_beginthread_wrapper (void *arg)
 333 {
 334   (void)thread_start_address (arg);
 335 }
 336
 337 int
 338 sys_thread_create (sys_thread_t *thread_ptr, const char *name,
 339                    thread_creation_function *func, void *arg)
 340 {
 341   /* FIXME: Do threads that run Lisp require some minimum amount of
 342      stack?  Zero here means each thread will get the same amount as
 343      the main program.  On GNU/Linux, it seems like the stack is 2MB
 344      by default, overridden by RLIMIT_STACK at program start time.
 345      Not sure what to do with this.  See also the comment in
 346      w32proc.c:new_child.  */
 347   const unsigned stack_size = 0;
 348   uintptr_t thandle;
 349
 350   thread_start_address = func;
 351
 352   /* We use _beginthread rather than CreateThread because the former
 353      arranges for the thread handle to be automatically closed when
 354      the thread exits, thus preventing handle leaks and/or the need to
 355      track all the threads and close their handles when they exit.
 356      Also, MSDN seems to imply that code which uses CRT _must_ call
 357      _beginthread, although if that is true, we already violate that
 358      rule in many places...  */
 359   thandle = _beginthread (w32_beginthread_wrapper, stack_size, arg);
 360   if (thandle == (uintptr_t)-1L)
 361     return 0;
 362
 363   /* Kludge alert!  We use the Windows thread ID, an unsigned 32-bit
 364      number, as the sys_thread_t type, because that ID is the only
 365      unique identifier of a thread on Windows.  But _beginthread
 366      returns a handle of the thread, and there's no easy way of
 367      getting the thread ID given a handle (GetThreadId is available
 368      only since Vista, so we cannot use it portably).  Fortunately,
 369      the value returned by sys_thread_create is not used by its
 370      callers; instead, run_thread, which runs in the context of the
 371      new thread, calls sys_thread_self and uses its return value;
 372      sys_thread_self in this implementation calls GetCurrentThreadId.
 373      Therefore, we return some more or less arbitrary value of the
 374      thread ID from this function. */
 375   *thread_ptr = thandle & 0xFFFFFFFF;
 376   return 1;
 377 }
 378
 379 void
 380 sys_thread_yield (void)
 381 {
 382   Sleep (0);
 383 }
 384
 385 #else
 386
 387 #error port me
 388
 389 #endif