dispatch/semaphore.h

   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
  29 /*!
  30  * @typedef dispatch_semaphore_t
  31  *
  32  * @abstract
  33  * A counting semaphore.
  34  */
  35 DISPATCH_DECL(dispatch_semaphore);
  36
  37 __BEGIN_DECLS
  38
  39 /*!
  40  * @function dispatch_semaphore_create
  41  *
  42  * @abstract
  43  * Creates new counting semaphore with an initial value.
  44  *
  45  * @discussion
  46  * Passing zero for the value is useful for when two threads need to reconcile
  47  * the completion of a particular event. Passing a value greather than zero is
  48  * useful for managing a finite pool of resources, where the pool size is equal
  49  * to the value.
  50  *
  51  * @param value
  52  * The starting value for the semaphore. Passing a value less than zero will
  53  * cause NULL to be returned.
  54  *
  55  * @result
  56  * The newly created semaphore, or NULL on failure.
  57  */
  58 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
  59 DISPATCH_EXPORT DISPATCH_MALLOC DISPATCH_RETURNS_RETAINED DISPATCH_WARN_RESULT
  60 DISPATCH_NOTHROW
  61 dispatch_semaphore_t
  62 dispatch_semaphore_create(long value);
  63
  64 /*!
  65  * @function dispatch_semaphore_wait
  66  *
  67  * @abstract
  68  * Wait (decrement) for a semaphore.
  69  *
  70  * @discussion
  71  * Decrement the counting semaphore. If the resulting value is less than zero,
  72  * this function waits for a signal to occur before returning.
  73  *
  74  * @param dsema
  75  * The semaphore. The result of passing NULL in this parameter is undefined.
  76  *
  77  * @param timeout
  78  * When to timeout (see dispatch_time). As a convenience, there are the
  79  * DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER constants.
  80  *
  81  * @result
  82  * Returns zero on success, or non-zero if the timeout occurred.
  83  */
  84 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
  85 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
  86 long
  87 dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);
  88
  89 /*!
  90  * @function dispatch_semaphore_signal
  91  *
  92  * @abstract
  93  * Signal (increment) a semaphore.
  94  *
  95  * @discussion
  96  * Increment the counting semaphore. If the previous value was less than zero,
  97  * this function wakes a waiting thread before returning.
  98  *
  99  * @param dsema The counting semaphore.
 100  * The result of passing NULL in this parameter is undefined.
 101  *
 102  * @result
 103  * This function returns non-zero if a thread is woken. Otherwise, zero is
 104  * returned.
 105  */
 106 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
 107 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
 108 long
 109 dispatch_semaphore_signal(dispatch_semaphore_t dsema);
 110
 111 __END_DECLS
 112
 113 #endif /* __DISPATCH_SEMAPHORE__ */