1/*
2 * Copyright (c) 2008-2013 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_SEMAPHORE__
22#define __DISPATCH_SEMAPHORE__
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
29DISPATCH_ASSUME_NONNULL_BEGIN
30DISPATCH_ASSUME_ABI_SINGLE_BEGIN
31
32/*!
33 * @typedef dispatch_semaphore_t
34 *
35 * @abstract
36 * A counting semaphore.
37 */
38DISPATCH_DECL_SWIFT(dispatch_semaphore, DispatchSemaphore);
39
40__BEGIN_DECLS
41
42/*!
43 * @function dispatch_semaphore_create
44 *
45 * @abstract
46 * Creates new counting semaphore with an initial value.
47 *
48 * @discussion
49 * Passing zero for the value is useful for when two threads need to reconcile
50 * the completion of a particular event. Passing a value greater than zero is
51 * useful for managing a finite pool of resources, where the pool size is equal
52 * to the value.
53 *
54 * @param value
55 * The starting value for the semaphore. Passing a value less than zero will
56 * cause NULL to be returned.
57 *
58 * @result
59 * The newly created semaphore, or NULL on failure.
60 */
61API_AVAILABLE(macos(10.6), ios(4.0))
62DISPATCH_EXPORT DISPATCH_MALLOC DISPATCH_RETURNS_RETAINED DISPATCH_WARN_RESULT
63DISPATCH_NOTHROW
64DISPATCH_SWIFT_NAME(DispatchSemaphore.init(value:))
65dispatch_semaphore_t
66dispatch_semaphore_create(intptr_t value);
67
68/*!
69 * @function dispatch_semaphore_wait
70 *
71 * @abstract
72 * Wait (decrement) for a semaphore.
73 *
74 * @discussion
75 * Decrement the counting semaphore. If the resulting value is less than zero,
76 * this function waits for a signal to occur before returning. If the timeout is
77 * reached without a signal being received, the semaphore is re-incremented
78 * before the function returns.
79 *
80 * @param dsema
81 * The semaphore. The result of passing NULL in this parameter is undefined.
82 *
83 * @param timeout
84 * When to timeout (see dispatch_time). As a convenience, there are the
85 * DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER constants.
86 *
87 * @result
88 * Returns zero on success, or non-zero if the timeout occurred.
89 */
90API_AVAILABLE(macos(10.6), ios(4.0))
91DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
92DISPATCH_REFINED_FOR_SWIFT
93intptr_t
94dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);
95
96/*!
97 * @function dispatch_semaphore_signal
98 *
99 * @abstract
100 * Signal (increment) a semaphore.
101 *
102 * @discussion
103 * Increment the counting semaphore. If the previous value was less than zero,
104 * this function wakes a waiting thread before returning.
105 *
106 * @param dsema The counting semaphore.
107 * The result of passing NULL in this parameter is undefined.
108 *
109 * @result
110 * This function returns non-zero if a thread is woken. Otherwise, zero is
111 * returned.
112 */
113API_AVAILABLE(macos(10.6), ios(4.0))
114DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
115DISPATCH_REFINED_FOR_SWIFT
116intptr_t
117dispatch_semaphore_signal(dispatch_semaphore_t dsema);
118
119__END_DECLS
120
121DISPATCH_ASSUME_ABI_SINGLE_END
122DISPATCH_ASSUME_NONNULL_END
123
124#endif /* __DISPATCH_SEMAPHORE__ */