1 /*
2 * Copyright (c) 2008-2010 Apple Inc. All rights reserved.
3 *
4 * @APPLE_APACHE_LICENSE_HEADER_START@
5 *
6 * Licensed under the Apache License, Version 2.0 (the "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 *
18 * @APPLE_APACHE_LICENSE_HEADER_END@
19 */
20
21 #ifndef __DISPATCH_ONCE__
22 #define __DISPATCH_ONCE__
23
24 #ifndef __DISPATCH_INDIRECT__
25 #error "Please #include <dispatch/dispatch.h> instead of this file directly."
26 #include <dispatch/base.h> // for HeaderDoc
27 #endif
28
29 DISPATCH_ASSUME_NONNULL_BEGIN
30
31 __BEGIN_DECLS
32
33 /*!
34 * @typedef dispatch_once_t
35 *
36 * @abstract
37 * A predicate for use with dispatch_once(). It must be initialized to zero.
38 * Note: static and global variables default to zero.
39 */
40 DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
41 typedef intptr_t dispatch_once_t;
42
43 #if defined(__x86_64__) || defined(__i386__) || defined(__s390x__)
44 #define DISPATCH_ONCE_INLINE_FASTPATH 1
45 #elif defined(__APPLE__)
46 #define DISPATCH_ONCE_INLINE_FASTPATH 1
47 #else
48 #define DISPATCH_ONCE_INLINE_FASTPATH 0
49 #endif
50
51 /*!
52 * @function dispatch_once
53 *
54 * @abstract
55 * Execute a block once and only once.
56 *
57 * @param predicate
58 * A pointer to a dispatch_once_t that is used to test whether the block has
59 * completed or not.
60 *
61 * @param block
62 * The block to execute once.
63 *
64 * @discussion
65 * Always call dispatch_once() before using or testing any variables that are
66 * initialized by the block.
67 */
68 #ifdef __BLOCKS__
69 API_AVAILABLE(macos(10.6), ios(4.0))
70 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
71 DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
72 void
73 dispatch_once(dispatch_once_t *predicate,
74 DISPATCH_NOESCAPE dispatch_block_t block);
75
76 #if DISPATCH_ONCE_INLINE_FASTPATH
77 DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
78 DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
79 void
_dispatch_once(dispatch_once_t * predicate,DISPATCH_NOESCAPE dispatch_block_t block)80 _dispatch_once(dispatch_once_t *predicate,
81 DISPATCH_NOESCAPE dispatch_block_t block)
82 {
83 if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
84 dispatch_once(predicate, block);
85 } else {
86 dispatch_compiler_barrier();
87 }
88 DISPATCH_COMPILER_CAN_ASSUME(*predicate == ~0l);
89 }
90 #undef dispatch_once
91 #define dispatch_once _dispatch_once
92 #endif
93 #endif // DISPATCH_ONCE_INLINE_FASTPATH
94
95 API_AVAILABLE(macos(10.6), ios(4.0))
96 DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
97 DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
98 void
99 dispatch_once_f(dispatch_once_t *predicate, void *_Nullable context,
100 dispatch_function_t function);
101
102 #if DISPATCH_ONCE_INLINE_FASTPATH
103 DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL1 DISPATCH_NONNULL3
104 DISPATCH_NOTHROW
105 DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
106 void
_dispatch_once_f(dispatch_once_t * predicate,void * _Nullable context,dispatch_function_t function)107 _dispatch_once_f(dispatch_once_t *predicate, void *_Nullable context,
108 dispatch_function_t function)
109 {
110 if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
111 dispatch_once_f(predicate, context, function);
112 } else {
113 dispatch_compiler_barrier();
114 }
115 DISPATCH_COMPILER_CAN_ASSUME(*predicate == ~0l);
116 }
117 #undef dispatch_once_f
118 #define dispatch_once_f _dispatch_once_f
119 #endif // DISPATCH_ONCE_INLINE_FASTPATH
120
121 __END_DECLS
122
123 DISPATCH_ASSUME_NONNULL_END
124
125 #endif