media/libvpx/vpx_ports/vpx_once.h@ac0c01689b40 (annotated)
media/libvpx/vpx_ports/vpx_once.h
Thu, 15 Jan 2015 15:59:08 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 15 Jan 2015 15:59:08 +0100
- branch
- TOR_BUG_9701
- changeset 10
- ac0c01689b40
- permissions
- -rw-r--r--
Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
| michael@0 | 1 | /* |
| michael@0 | 2 | * Copyright (c) 2011 The WebM project authors. All Rights Reserved. |
| michael@0 | 3 | * |
| michael@0 | 4 | * Use of this source code is governed by a BSD-style license |
| michael@0 | 5 | * that can be found in the LICENSE file in the root of the source |
| michael@0 | 6 | * tree. An additional intellectual property rights grant can be found |
| michael@0 | 7 | * in the file PATENTS. All contributing project authors may |
| michael@0 | 8 | * be found in the AUTHORS file in the root of the source tree. |
| michael@0 | 9 | */ |
| michael@0 | 10 | #ifndef VPX_ONCE_H |
| michael@0 | 11 | #define VPX_ONCE_H |
| michael@0 | 12 | |
| michael@0 | 13 | #include "vpx_config.h" |
| michael@0 | 14 | |
| michael@0 | 15 | #if CONFIG_MULTITHREAD && defined(_WIN32) |
| michael@0 | 16 | #include <windows.h> |
| michael@0 | 17 | #include <stdlib.h> |
| michael@0 | 18 | static void once(void (*func)(void)) |
| michael@0 | 19 | { |
| michael@0 | 20 | static CRITICAL_SECTION *lock; |
| michael@0 | 21 | static LONG waiters; |
| michael@0 | 22 | static int done; |
| michael@0 | 23 | void *lock_ptr = &lock; |
| michael@0 | 24 | |
| michael@0 | 25 | /* If the initialization is complete, return early. This isn't just an |
| michael@0 | 26 | * optimization, it prevents races on the destruction of the global |
| michael@0 | 27 | * lock. |
| michael@0 | 28 | */ |
| michael@0 | 29 | if(done) |
| michael@0 | 30 | return; |
| michael@0 | 31 | |
| michael@0 | 32 | InterlockedIncrement(&waiters); |
| michael@0 | 33 | |
| michael@0 | 34 | /* Get a lock. We create one and try to make it the one-true-lock, |
| michael@0 | 35 | * throwing it away if we lost the race. |
| michael@0 | 36 | */ |
| michael@0 | 37 | |
| michael@0 | 38 | { |
| michael@0 | 39 | /* Scope to protect access to new_lock */ |
| michael@0 | 40 | CRITICAL_SECTION *new_lock = malloc(sizeof(CRITICAL_SECTION)); |
| michael@0 | 41 | InitializeCriticalSection(new_lock); |
| michael@0 | 42 | if (InterlockedCompareExchangePointer(lock_ptr, new_lock, NULL) != NULL) |
| michael@0 | 43 | { |
| michael@0 | 44 | DeleteCriticalSection(new_lock); |
| michael@0 | 45 | free(new_lock); |
| michael@0 | 46 | } |
| michael@0 | 47 | } |
| michael@0 | 48 | |
| michael@0 | 49 | /* At this point, we have a lock that can be synchronized on. We don't |
| michael@0 | 50 | * care which thread actually performed the allocation. |
| michael@0 | 51 | */ |
| michael@0 | 52 | |
| michael@0 | 53 | EnterCriticalSection(lock); |
| michael@0 | 54 | |
| michael@0 | 55 | if (!done) |
| michael@0 | 56 | { |
| michael@0 | 57 | func(); |
| michael@0 | 58 | done = 1; |
| michael@0 | 59 | } |
| michael@0 | 60 | |
| michael@0 | 61 | LeaveCriticalSection(lock); |
| michael@0 | 62 | |
| michael@0 | 63 | /* Last one out should free resources. The destructed objects are |
| michael@0 | 64 | * protected by checking if(done) above. |
| michael@0 | 65 | */ |
| michael@0 | 66 | if(!InterlockedDecrement(&waiters)) |
| michael@0 | 67 | { |
| michael@0 | 68 | DeleteCriticalSection(lock); |
| michael@0 | 69 | free(lock); |
| michael@0 | 70 | lock = NULL; |
| michael@0 | 71 | } |
| michael@0 | 72 | } |
| michael@0 | 73 | |
| michael@0 | 74 | |
| michael@0 | 75 | #elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H |
| michael@0 | 76 | #include <pthread.h> |
| michael@0 | 77 | static void once(void (*func)(void)) |
| michael@0 | 78 | { |
| michael@0 | 79 | static pthread_once_t lock = PTHREAD_ONCE_INIT; |
| michael@0 | 80 | pthread_once(&lock, func); |
| michael@0 | 81 | } |
| michael@0 | 82 | |
| michael@0 | 83 | |
| michael@0 | 84 | #else |
| michael@0 | 85 | /* No-op version that performs no synchronization. vp8_rtcd() is idempotent, |
| michael@0 | 86 | * so as long as your platform provides atomic loads/stores of pointers |
| michael@0 | 87 | * no synchronization is strictly necessary. |
| michael@0 | 88 | */ |
| michael@0 | 89 | |
| michael@0 | 90 | static void once(void (*func)(void)) |
| michael@0 | 91 | { |
| michael@0 | 92 | static int done; |
| michael@0 | 93 | |
| michael@0 | 94 | if(!done) |
| michael@0 | 95 | { |
| michael@0 | 96 | func(); |
| michael@0 | 97 | done = 1; |
| michael@0 | 98 | } |
| michael@0 | 99 | } |
| michael@0 | 100 | #endif |
| michael@0 | 101 | |
| michael@0 | 102 | #endif |
