src/semaphore.c

   1 /*
   2  * Copyright (c) 2008-2013 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_APACHE_LICENSE_HEADER_START@
   5  *
   6  * Licensed under the Apache License, Version 2.0 (the "License");
   7  * you may not use this file except in compliance with the License.
   8  * You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  *
  18  * @APPLE_APACHE_LICENSE_HEADER_END@
  19  */
  20
  21 #include "internal.h"
  22
  23 DISPATCH_WEAK // rdar://problem/8503746
  24 long _dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema);
  25
  26 #pragma mark -
  27 #pragma mark dispatch_semaphore_class_t
  28
  29 static void
  30 _dispatch_semaphore_class_init(long value, dispatch_semaphore_class_t dsemau)
  31 {
  32         struct dispatch_semaphore_header_s *dsema = dsemau._dsema_hdr;
  33
  34         dsema->do_next = DISPATCH_OBJECT_LISTLESS;
  35         dsema->do_targetq = _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT,
  36                         false);
  37         dsema->dsema_value = value;
  38         _os_semaphore_init(&dsema->dsema_sema, _OS_SEM_POLICY_FIFO);
  39 }
  40
  41 #pragma mark -
  42 #pragma mark dispatch_semaphore_t
  43
  44 dispatch_semaphore_t
  45 dispatch_semaphore_create(long value)
  46 {
  47         dispatch_semaphore_t dsema;
  48
  49         // If the internal value is negative, then the absolute of the value is
  50         // equal to the number of waiting threads. Therefore it is bogus to
  51         // initialize the semaphore with a negative value.
  52         if (value < 0) {
  53                 return DISPATCH_BAD_INPUT;
  54         }
  55
  56         dsema = (dispatch_semaphore_t)_dispatch_alloc(DISPATCH_VTABLE(semaphore),
  57                         sizeof(struct dispatch_semaphore_s));
  58         _dispatch_semaphore_class_init(value, dsema);
  59         dsema->dsema_orig = value;
  60         return dsema;
  61 }
  62
  63 void
  64 _dispatch_semaphore_dispose(dispatch_object_t dou)
  65 {
  66         dispatch_semaphore_t dsema = dou._dsema;
  67
  68         if (dsema->dsema_value < dsema->dsema_orig) {
  69                 DISPATCH_CLIENT_CRASH(dsema->dsema_orig - dsema->dsema_value,
  70                                 "Semaphore object deallocated while in use");
  71         }
  72
  73         _os_semaphore_dispose(&dsema->dsema_sema);
  74 }
  75
  76 size_t
  77 _dispatch_semaphore_debug(dispatch_object_t dou, char *buf, size_t bufsiz)
  78 {
  79         dispatch_semaphore_t dsema = dou._dsema;
  80
  81         size_t offset = 0;
  82         offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
  83                         dx_kind(dsema), dsema);
  84         offset += _dispatch_object_debug_attr(dsema, &buf[offset], bufsiz - offset);
  85 #if USE_MACH_SEM
  86         offset += dsnprintf(&buf[offset], bufsiz - offset, "port = 0x%u, ",
  87                         dsema->dsema_sema);
  88 #endif
  89         offset += dsnprintf(&buf[offset], bufsiz - offset,
  90                         "value = %ld, orig = %ld }", dsema->dsema_value, dsema->dsema_orig);
  91         return offset;
  92 }
  93
  94 DISPATCH_NOINLINE
  95 long
  96 _dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema)
  97 {
  98         _os_semaphore_create(&dsema->dsema_sema, _OS_SEM_POLICY_FIFO);
  99         _os_semaphore_signal(&dsema->dsema_sema, 1);
 100         return 1;
 101 }
 102
 103 long
 104 dispatch_semaphore_signal(dispatch_semaphore_t dsema)
 105 {
 106         long value = os_atomic_inc2o(dsema, dsema_value, release);
 107         if (fastpath(value > 0)) {
 108                 return 0;
 109         }
 110         if (slowpath(value == LONG_MIN)) {
 111                 DISPATCH_CLIENT_CRASH(value,
 112                                 "Unbalanced call to dispatch_semaphore_signal()");
 113         }
 114         return _dispatch_semaphore_signal_slow(dsema);
 115 }
 116
 117 DISPATCH_NOINLINE
 118 static long
 119 _dispatch_semaphore_wait_slow(dispatch_semaphore_t dsema,
 120                 dispatch_time_t timeout)
 121 {
 122         long orig;
 123
 124         _os_semaphore_create(&dsema->dsema_sema, _OS_SEM_POLICY_FIFO);
 125         switch (timeout) {
 126         default:
 127                 if (!_os_semaphore_timedwait(&dsema->dsema_sema, timeout)) {
 128                         break;
 129                 }
 130                 // Fall through and try to undo what the fast path did to
 131                 // dsema->dsema_value
 132         case DISPATCH_TIME_NOW:
 133                 orig = dsema->dsema_value;
 134                 while (orig < 0) {
 135                         if (os_atomic_cmpxchgvw2o(dsema, dsema_value, orig, orig + 1,
 136                                         &orig, relaxed)) {
 137                                 return _OS_SEM_TIMEOUT();
 138                         }
 139                 }
 140                 // Another thread called semaphore_signal().
 141                 // Fall through and drain the wakeup.
 142         case DISPATCH_TIME_FOREVER:
 143                 _os_semaphore_wait(&dsema->dsema_sema);
 144                 break;
 145         }
 146         return 0;
 147 }
 148
 149 long
 150 dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout)
 151 {
 152         long value = os_atomic_dec2o(dsema, dsema_value, acquire);
 153         if (fastpath(value >= 0)) {
 154                 return 0;
 155         }
 156         return _dispatch_semaphore_wait_slow(dsema, timeout);
 157 }
 158
 159 #pragma mark -
 160 #pragma mark dispatch_group_t
 161
 162 DISPATCH_ALWAYS_INLINE
 163 static inline dispatch_group_t
 164 _dispatch_group_create_with_count(long count)
 165 {
 166         dispatch_group_t dg = (dispatch_group_t)_dispatch_alloc(
 167                         DISPATCH_VTABLE(group), sizeof(struct dispatch_group_s));
 168         _dispatch_semaphore_class_init(count, dg);
 169         if (count) {
 170                 os_atomic_store2o(dg, do_ref_cnt, 1, relaxed); // <rdar://problem/22318411>
 171         }
 172         return dg;
 173 }
 174
 175 dispatch_group_t
 176 dispatch_group_create(void)
 177 {
 178         return _dispatch_group_create_with_count(0);
 179 }
 180
 181 dispatch_group_t
 182 _dispatch_group_create_and_enter(void)
 183 {
 184         return _dispatch_group_create_with_count(1);
 185 }
 186
 187 void
 188 dispatch_group_enter(dispatch_group_t dg)
 189 {
 190         long value = os_atomic_inc_orig2o(dg, dg_value, acquire);
 191         if (slowpath((unsigned long)value >= (unsigned long)LONG_MAX)) {
 192                 DISPATCH_CLIENT_CRASH(value,
 193                                 "Too many nested calls to dispatch_group_enter()");
 194         }
 195         if (value == 0) {
 196                 _dispatch_retain(dg); // <rdar://problem/22318411>
 197         }
 198 }
 199
 200 DISPATCH_NOINLINE
 201 static long
 202 _dispatch_group_wake(dispatch_group_t dg, bool needs_release)
 203 {
 204         dispatch_continuation_t next, head, tail = NULL;
 205         long rval;
 206
 207         // cannot use os_mpsc_capture_snapshot() because we can have concurrent
 208         // _dispatch_group_wake() calls
 209         head = os_atomic_xchg2o(dg, dg_notify_head, NULL, relaxed);
 210         if (head) {
 211                 // snapshot before anything is notified/woken <rdar://problem/8554546>
 212                 tail = os_atomic_xchg2o(dg, dg_notify_tail, NULL, release);
 213         }
 214         rval = (long)os_atomic_xchg2o(dg, dg_waiters, 0, relaxed);
 215         if (rval) {
 216                 // wake group waiters
 217                 _os_semaphore_create(&dg->dg_sema, _OS_SEM_POLICY_FIFO);
 218                 _os_semaphore_signal(&dg->dg_sema, rval);
 219         }
 220         if (head) {
 221                 // async group notify blocks
 222                 do {
 223                         next = os_mpsc_pop_snapshot_head(head, tail, do_next);
 224                         dispatch_queue_t dsn_queue = (dispatch_queue_t)head->dc_data;
 225                         _dispatch_continuation_async(dsn_queue, head);
 226                         _dispatch_release(dsn_queue);
 227                 } while ((head = next));
 228                 _dispatch_release(dg);
 229         }
 230         if (needs_release) {
 231                 _dispatch_release(dg); // <rdar://problem/22318411>
 232         }
 233         return 0;
 234 }
 235
 236 void
 237 dispatch_group_leave(dispatch_group_t dg)
 238 {
 239         long value = os_atomic_dec2o(dg, dg_value, release);
 240         if (slowpath(value == 0)) {
 241                 return (void)_dispatch_group_wake(dg, true);
 242         }
 243         if (slowpath(value < 0)) {
 244                 DISPATCH_CLIENT_CRASH(value,
 245                                 "Unbalanced call to dispatch_group_leave()");
 246         }
 247 }
 248
 249 void
 250 _dispatch_group_dispose(dispatch_object_t dou)
 251 {
 252         dispatch_group_t dg = dou._dg;
 253
 254         if (dg->dg_value) {
 255                 DISPATCH_CLIENT_CRASH(dg->dg_value,
 256                                 "Group object deallocated while in use");
 257         }
 258
 259         _os_semaphore_dispose(&dg->dg_sema);
 260 }
 261
 262 size_t
 263 _dispatch_group_debug(dispatch_object_t dou, char *buf, size_t bufsiz)
 264 {
 265         dispatch_group_t dg = dou._dg;
 266
 267         size_t offset = 0;
 268         offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
 269                         dx_kind(dg), dg);
 270         offset += _dispatch_object_debug_attr(dg, &buf[offset], bufsiz - offset);
 271 #if USE_MACH_SEM
 272         offset += dsnprintf(&buf[offset], bufsiz - offset, "port = 0x%u, ",
 273                         dg->dg_sema);
 274 #endif
 275         offset += dsnprintf(&buf[offset], bufsiz - offset,
 276                         "count = %ld, waiters = %d }", dg->dg_value, dg->dg_waiters);
 277         return offset;
 278 }
 279
 280 DISPATCH_NOINLINE
 281 static long
 282 _dispatch_group_wait_slow(dispatch_group_t dg, dispatch_time_t timeout)
 283 {
 284         long value;
 285         int orig_waiters;
 286
 287         // check before we cause another signal to be sent by incrementing
 288         // dg->dg_waiters
 289         value = os_atomic_load2o(dg, dg_value, ordered); // 19296565
 290         if (value == 0) {
 291                 return _dispatch_group_wake(dg, false);
 292         }
 293
 294         (void)os_atomic_inc2o(dg, dg_waiters, relaxed);
 295         // check the values again in case we need to wake any threads
 296         value = os_atomic_load2o(dg, dg_value, ordered); // 19296565
 297         if (value == 0) {
 298                 _dispatch_group_wake(dg, false);
 299                 // Fall through to consume the extra signal, forcing timeout to avoid
 300                 // useless setups as it won't block
 301                 timeout = DISPATCH_TIME_FOREVER;
 302         }
 303
 304         _os_semaphore_create(&dg->dg_sema, _OS_SEM_POLICY_FIFO);
 305         switch (timeout) {
 306         default:
 307                 if (!_os_semaphore_timedwait(&dg->dg_sema, timeout)) {
 308                         break;
 309                 }
 310                 // Fall through and try to undo the earlier change to
 311                 // dg->dg_waiters
 312         case DISPATCH_TIME_NOW:
 313                 orig_waiters = dg->dg_waiters;
 314                 while (orig_waiters) {
 315                         if (os_atomic_cmpxchgvw2o(dg, dg_waiters, orig_waiters,
 316                                         orig_waiters - 1, &orig_waiters, relaxed)) {
 317                                 return _OS_SEM_TIMEOUT();
 318                         }
 319                 }
 320                 // Another thread is running _dispatch_group_wake()
 321                 // Fall through and drain the wakeup.
 322         case DISPATCH_TIME_FOREVER:
 323                 _os_semaphore_wait(&dg->dg_sema);
 324                 break;
 325         }
 326         return 0;
 327 }
 328
 329 long
 330 dispatch_group_wait(dispatch_group_t dg, dispatch_time_t timeout)
 331 {
 332         if (dg->dg_value == 0) {
 333                 return 0;
 334         }
 335         if (timeout == 0) {
 336                 return _OS_SEM_TIMEOUT();
 337         }
 338         return _dispatch_group_wait_slow(dg, timeout);
 339 }
 340
 341 DISPATCH_ALWAYS_INLINE
 342 static inline void
 343 _dispatch_group_notify(dispatch_group_t dg, dispatch_queue_t dq,
 344                 dispatch_continuation_t dsn)
 345 {
 346         dsn->dc_data = dq;
 347         dsn->do_next = NULL;
 348         _dispatch_retain(dq);
 349         if (os_mpsc_push_update_tail(dg, dg_notify, dsn, do_next)) {
 350                 _dispatch_retain(dg);
 351                 os_atomic_store2o(dg, dg_notify_head, dsn, ordered);
 352                 // seq_cst with atomic store to notify_head <rdar://problem/11750916>
 353                 if (os_atomic_load2o(dg, dg_value, ordered) == 0) {
 354                         _dispatch_group_wake(dg, false);
 355                 }
 356         }
 357 }
 358
 359 DISPATCH_NOINLINE
 360 void
 361 dispatch_group_notify_f(dispatch_group_t dg, dispatch_queue_t dq, void *ctxt,
 362                 dispatch_function_t func)
 363 {
 364         dispatch_continuation_t dsn = _dispatch_continuation_alloc();
 365         _dispatch_continuation_init_f(dsn, dq, ctxt, func, 0, 0,
 366                         DISPATCH_OBJ_CONSUME_BIT);
 367         _dispatch_group_notify(dg, dq, dsn);
 368 }
 369
 370 #ifdef __BLOCKS__
 371 void
 372 dispatch_group_notify(dispatch_group_t dg, dispatch_queue_t dq,
 373                 dispatch_block_t db)
 374 {
 375         dispatch_continuation_t dsn = _dispatch_continuation_alloc();
 376         _dispatch_continuation_init(dsn, dq, db, 0, 0, DISPATCH_OBJ_CONSUME_BIT);
 377         _dispatch_group_notify(dg, dq, dsn);
 378 }
 379 #endif