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 #include <windows.h>
43 /* Declare a per-compilation-unit state variable to track the progress
44 * of calling func() only once. This must be at global scope because
45 * local initializers are not thread-safe in MSVC prior to Visual
46 * Studio 2015.
47 */
48 static INIT_ONCE aom_init_once = INIT_ONCE_STATIC_INIT;
49
aom_once(void (* func)(void))50 static void aom_once(void (*func)(void)) {
51 BOOL pending;
52 InitOnceBeginInitialize(&aom_init_once, 0, &pending, NULL);
53 if (!pending) {
54 // Initialization has already completed.
55 return;
56 }
57 func();
58 InitOnceComplete(&aom_init_once, 0, NULL);
59 }
60
61 #elif CONFIG_MULTITHREAD && defined(__OS2__)
62 #define INCL_DOS
63 #include <os2.h>
aom_once(void (* func)(void))64 static void aom_once(void (*func)(void)) {
65 static int done;
66
67 /* If the initialization is complete, return early. */
68 if (done) return;
69
70 /* Causes all other threads in the process to block themselves
71 * and give up their time slice.
72 */
73 DosEnterCritSec();
74
75 if (!done) {
76 func();
77 done = 1;
78 }
79
80 /* Restores normal thread dispatching for the current process. */
81 DosExitCritSec();
82 }
83
84 #elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
85 #include <pthread.h>
aom_once(void (* func)(void))86 static void aom_once(void (*func)(void)) {
87 static pthread_once_t lock = PTHREAD_ONCE_INIT;
88 pthread_once(&lock, func);
89 }
90
91 #else
92 /* Default version that performs no synchronization. */
93
aom_once(void (* func)(void))94 static void aom_once(void (*func)(void)) {
95 static int done;
96
97 if (!done) {
98 func();
99 done = 1;
100 }
101 }
102 #endif
103
104 #endif // AOM_AOM_PORTS_AOM_ONCE_H_
105