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/*
* Copyright (c) 2016, Alliance for Open Media. All rights reserved
*
* This source code is subject to the terms of the BSD 2 Clause License and
* the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
* was not distributed with this source code in the LICENSE file, you can
* obtain it at www.aomedia.org/license/software. If the Alliance for Open
* Media Patent License 1.0 was not distributed with this source code in the
* PATENTS file, you can obtain it at www.aomedia.org/license/patent.
*/
#ifndef AOM_AOM_PORTS_AOM_ONCE_H_
#define AOM_AOM_PORTS_AOM_ONCE_H_
#include "config/aom_config.h"
/* Implement a function wrapper to guarantee initialization
* thread-safety for library singletons.
*
* NOTE: This function uses static locks, and can only be
* used with one common argument per compilation unit. So
*
* file1.c:
* aom_once(foo);
* ...
* aom_once(foo);
*
* file2.c:
* aom_once(bar);
*
* will ensure foo() and bar() are each called only once, but in
*
* file1.c:
* aom_once(foo);
* aom_once(bar):
*
* bar() will never be called because the lock is used up
* by the call to foo().
*/
#if CONFIG_MULTITHREAD && defined(_WIN32)
#undef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
/* Declare a per-compilation-unit state variable to track the progress
* of calling func() only once. This must be at global scope because
* local initializers are not thread-safe in MSVC prior to Visual
* Studio 2015.
*/
static INIT_ONCE aom_init_once = INIT_ONCE_STATIC_INIT;
static void aom_once(void (*func)(void)) {
BOOL pending;
InitOnceBeginInitialize(&aom_init_once, 0, &pending, NULL);
if (!pending) {
// Initialization has already completed.
return;
}
func();
InitOnceComplete(&aom_init_once, 0, NULL);
}
#elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
#include <pthread.h>
static void aom_once(void (*func)(void)) {
static pthread_once_t lock = PTHREAD_ONCE_INIT;
pthread_once(&lock, func);
}
#else
/* Default version that performs no synchronization. */
static void aom_once(void (*func)(void)) {
static volatile int done;
if (!done) {
func();
done = 1;
}
}
#endif
#endif // AOM_AOM_PORTS_AOM_ONCE_H_
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