98 строки
2.4 KiB
C
98 строки
2.4 KiB
C
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/*
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* Copyright (c) 2011 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "vpx_config.h"
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#if CONFIG_MULTITHREAD && defined(_WIN32)
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#include <windows.h>
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#include <stdlib.h>
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static void once(void (*func)(void))
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{
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static CRITICAL_SECTION *lock;
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static LONG waiters;
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static int done;
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void *lock_ptr = &lock;
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/* If the initialization is complete, return early. This isn't just an
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* optimization, it prevents races on the destruction of the global
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* lock.
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*/
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if(done)
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return;
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InterlockedIncrement(&waiters);
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/* Get a lock. We create one and try to make it the one-true-lock,
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* throwing it away if we lost the race.
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*/
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{
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/* Scope to protect access to new_lock */
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CRITICAL_SECTION *new_lock = malloc(sizeof(CRITICAL_SECTION));
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InitializeCriticalSection(new_lock);
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if (InterlockedCompareExchangePointer(lock_ptr, new_lock, NULL) != NULL)
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{
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DeleteCriticalSection(new_lock);
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free(new_lock);
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}
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}
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/* At this point, we have a lock that can be synchronized on. We don't
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* care which thread actually performed the allocation.
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*/
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EnterCriticalSection(lock);
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if (!done)
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{
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func();
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done = 1;
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}
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LeaveCriticalSection(lock);
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/* Last one out should free resources. The destructed objects are
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* protected by checking if(done) above.
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*/
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if(!InterlockedDecrement(&waiters))
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{
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DeleteCriticalSection(lock);
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free(lock);
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lock = NULL;
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}
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}
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#elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
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#include <pthread.h>
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static void once(void (*func)(void))
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{
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static pthread_once_t lock = PTHREAD_ONCE_INIT;
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pthread_once(&lock, func);
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}
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#else
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/* No-op version that performs no synchronization. vp8_rtcd() is idempotent,
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* so as long as your platform provides atomic loads/stores of pointers
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* no synchronization is strictly necessary.
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*/
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static void once(void (*func)(void))
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{
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static int done;
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if(!done)
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{
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func();
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done = 1;
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}
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}
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#endif
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