105 lines
2.6 KiB
C
105 lines
2.6 KiB
C
/*
|
|
* 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)
|
|
#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 && defined(__OS2__)
|
|
#define INCL_DOS
|
|
#include <os2.h>
|
|
static void aom_once(void (*func)(void)) {
|
|
static volatile int done;
|
|
|
|
/* If the initialization is complete, return early. */
|
|
if (done) return;
|
|
|
|
/* Causes all other threads in the process to block themselves
|
|
* and give up their time slice.
|
|
*/
|
|
DosEnterCritSec();
|
|
|
|
if (!done) {
|
|
func();
|
|
done = 1;
|
|
}
|
|
|
|
/* Restores normal thread dispatching for the current process. */
|
|
DosExitCritSec();
|
|
}
|
|
|
|
#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_
|