From 68569dee1416593955c1570d638b3d9250b33012 Mon Sep 17 00:00:00 2001 From: trav90 Date: Mon, 15 Oct 2018 21:45:30 -0500 Subject: Import aom library This is the reference implementation for the Alliance for Open Media's av1 video code. The commit used was 4d668d7feb1f8abd809d1bca0418570a7f142a36. --- third_party/aom/aom_ports/aom_once.h | 141 +++++++++++++++++++++++++++++++++++ 1 file changed, 141 insertions(+) create mode 100644 third_party/aom/aom_ports/aom_once.h (limited to 'third_party/aom/aom_ports/aom_once.h') diff --git a/third_party/aom/aom_ports/aom_once.h b/third_party/aom/aom_ports/aom_once.h new file mode 100644 index 000000000..3cfd2fd95 --- /dev/null +++ b/third_party/aom/aom_ports/aom_once.h @@ -0,0 +1,141 @@ +/* + * 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_PORTS_AOM_ONCE_H_ +#define AOM_PORTS_AOM_ONCE_H_ + +#include "aom_config.h" + +/* Implement a function wrapper to guarantee initialization + * thread-safety for library singletons. + * + * NOTE: These functions use 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 +#include +/* 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. + * + * As a static, once_state will be zero-initialized as program start. + */ +static LONG once_state; +static void once(void (*func)(void)) { + /* Try to advance once_state from its initial value of 0 to 1. + * Only one thread can succeed in doing so. + */ + if (InterlockedCompareExchange(&once_state, 1, 0) == 0) { + /* We're the winning thread, having set once_state to 1. + * Call our function. */ + func(); + /* Now advance once_state to 2, unblocking any other threads. */ + InterlockedIncrement(&once_state); + return; + } + + /* We weren't the winning thread, but we want to block on + * the state variable so we don't return before func() + * has finished executing elsewhere. + * + * Try to advance once_state from 2 to 2, which is only possible + * after the winning thead advances it from 1 to 2. + */ + while (InterlockedCompareExchange(&once_state, 2, 2) != 2) { + /* State isn't yet 2. Try again. + * + * We are used for singleton initialization functions, + * which should complete quickly. Contention will likewise + * be rare, so it's worthwhile to use a simple but cpu- + * intensive busy-wait instead of successive backoff, + * waiting on a kernel object, or another heavier-weight scheme. + * + * We can at least yield our timeslice. + */ + Sleep(0); + } + + /* We've seen once_state advance to 2, so we know func() + * has been called. And we've left once_state as we found it, + * so other threads will have the same experience. + * + * It's safe to return now. + */ + return; +} + +#elif CONFIG_MULTITHREAD && defined(__OS2__) +#define INCL_DOS +#include +static void once(void (*func)(void)) { + static 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 +static void once(void (*func)(void)) { + static pthread_once_t lock = PTHREAD_ONCE_INIT; + pthread_once(&lock, func); +} + +#else +/* No-op version that performs no synchronization. *_rtcd() is idempotent, + * so as long as your platform provides atomic loads/stores of pointers + * no synchronization is strictly necessary. + */ + +static void once(void (*func)(void)) { + static int done; + + if (!done) { + func(); + done = 1; + } +} +#endif + +#endif // AOM_PORTS_AOM_ONCE_H_ -- cgit v1.2.3