1 /*
2 * Copyright (c) 2016, Alliance for Open Media. All rights reserved.
3 *
4 * This source code is subject to the terms of the BSD 2 Clause License and
5 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
6 * was not distributed with this source code in the LICENSE file, you can
7 * obtain it at www.aomedia.org/license/software. If the Alliance for Open
8 * Media Patent License 1.0 was not distributed with this source code in the
9 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
10 */
11
12 #ifndef AOM_AOM_PORTS_AOM_ONCE_H_
13 #define AOM_AOM_PORTS_AOM_ONCE_H_
14
15 #include "config/aom_config.h"
16
17 /* Implement a function wrapper to guarantee initialization
18 * thread-safety for library singletons.
19 *
20 * NOTE: This function uses static locks, and can only be
21 * used with one common argument per compilation unit. So
22 *
23 * file1.c:
24 * aom_once(foo);
25 * ...
26 * aom_once(foo);
27 *
28 * file2.c:
29 * aom_once(bar);
30 *
31 * will ensure foo() and bar() are each called only once, but in
32 *
33 * file1.c:
34 * aom_once(foo);
35 * aom_once(bar):
36 *
37 * bar() will never be called because the lock is used up
38 * by the call to foo().
39 */
40
41 #if CONFIG_MULTITHREAD && defined(_WIN32)
42 #undef WIN32_LEAN_AND_MEAN
43 #define WIN32_LEAN_AND_MEAN
44 #include <windows.h>
45 /* Declare a per-compilation-unit state variable to track the progress
46 * of calling func() only once. This must be at global scope because
47 * local initializers are not thread-safe in MSVC prior to Visual
48 * Studio 2015.
49 */
50 static INIT_ONCE aom_init_once = INIT_ONCE_STATIC_INIT;
51
aom_once(void (* func)(void))52 static void aom_once(void (*func)(void)) {
53 BOOL pending;
54 InitOnceBeginInitialize(&aom_init_once, 0, &pending, NULL);
55 if (!pending) {
56 // Initialization has already completed.
57 return;
58 }
59 func();
60 InitOnceComplete(&aom_init_once, 0, NULL);
61 }
62
63 #elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
64 #include <pthread.h>
aom_once(void (* func)(void))65 static void aom_once(void (*func)(void)) {
66 static pthread_once_t lock = PTHREAD_ONCE_INIT;
67 pthread_once(&lock, func);
68 }
69
70 #else
71 /* Default version that performs no synchronization. */
72
aom_once(void (* func)(void))73 static void aom_once(void (*func)(void)) {
74 static volatile int done;
75
76 if (!done) {
77 func();
78 done = 1;
79 }
80 }
81 #endif
82
83 #endif // AOM_AOM_PORTS_AOM_ONCE_H_
84