The Tor Browser / file comparison
comparison: media/libvpx/vpx_ports/vpx_once.h
media/libvpx/vpx_ports/vpx_once.h
- branch
- TOR_BUG_9701
- changeset 10
- ac0c01689b40
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| -1:000000000000 | 0:cb9d008e2897 |
|---|---|
| 1 /* | |
| 2 * Copyright (c) 2011 The WebM project authors. All Rights Reserved. | |
| 3 * | |
| 4 * Use of this source code is governed by a BSD-style license | |
| 5 * that can be found in the LICENSE file in the root of the source | |
| 6 * tree. An additional intellectual property rights grant can be found | |
| 7 * in the file PATENTS. All contributing project authors may | |
| 8 * be found in the AUTHORS file in the root of the source tree. | |
| 9 */ | |
| 10 #ifndef VPX_ONCE_H | |
| 11 #define VPX_ONCE_H | |
| 12 | |
| 13 #include "vpx_config.h" | |
| 14 | |
| 15 #if CONFIG_MULTITHREAD && defined(_WIN32) | |
| 16 #include <windows.h> | |
| 17 #include <stdlib.h> | |
| 18 static void once(void (*func)(void)) | |
| 19 { | |
| 20 static CRITICAL_SECTION *lock; | |
| 21 static LONG waiters; | |
| 22 static int done; | |
| 23 void *lock_ptr = &lock; | |
| 24 | |
| 25 /* If the initialization is complete, return early. This isn't just an | |
| 26 * optimization, it prevents races on the destruction of the global | |
| 27 * lock. | |
| 28 */ | |
| 29 if(done) | |
| 30 return; | |
| 31 | |
| 32 InterlockedIncrement(&waiters); | |
| 33 | |
| 34 /* Get a lock. We create one and try to make it the one-true-lock, | |
| 35 * throwing it away if we lost the race. | |
| 36 */ | |
| 37 | |
| 38 { | |
| 39 /* Scope to protect access to new_lock */ | |
| 40 CRITICAL_SECTION *new_lock = malloc(sizeof(CRITICAL_SECTION)); | |
| 41 InitializeCriticalSection(new_lock); | |
| 42 if (InterlockedCompareExchangePointer(lock_ptr, new_lock, NULL) != NULL) | |
| 43 { | |
| 44 DeleteCriticalSection(new_lock); | |
| 45 free(new_lock); | |
| 46 } | |
| 47 } | |
| 48 | |
| 49 /* At this point, we have a lock that can be synchronized on. We don't | |
| 50 * care which thread actually performed the allocation. | |
| 51 */ | |
| 52 | |
| 53 EnterCriticalSection(lock); | |
| 54 | |
| 55 if (!done) | |
| 56 { | |
| 57 func(); | |
| 58 done = 1; | |
| 59 } | |
| 60 | |
| 61 LeaveCriticalSection(lock); | |
| 62 | |
| 63 /* Last one out should free resources. The destructed objects are | |
| 64 * protected by checking if(done) above. | |
| 65 */ | |
| 66 if(!InterlockedDecrement(&waiters)) | |
| 67 { | |
| 68 DeleteCriticalSection(lock); | |
| 69 free(lock); | |
| 70 lock = NULL; | |
| 71 } | |
| 72 } | |
| 73 | |
| 74 | |
| 75 #elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H | |
| 76 #include <pthread.h> | |
| 77 static void once(void (*func)(void)) | |
| 78 { | |
| 79 static pthread_once_t lock = PTHREAD_ONCE_INIT; | |
| 80 pthread_once(&lock, func); | |
| 81 } | |
| 82 | |
| 83 | |
| 84 #else | |
| 85 /* No-op version that performs no synchronization. vp8_rtcd() is idempotent, | |
| 86 * so as long as your platform provides atomic loads/stores of pointers | |
| 87 * no synchronization is strictly necessary. | |
| 88 */ | |
| 89 | |
| 90 static void once(void (*func)(void)) | |
| 91 { | |
| 92 static int done; | |
| 93 | |
| 94 if(!done) | |
| 95 { | |
| 96 func(); | |
| 97 done = 1; | |
| 98 } | |
| 99 } | |
| 100 #endif | |
| 101 | |
| 102 #endif |
