src/semaphore.h

   1 /*
   2  * Copyright (c) 2008-2009 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_NA)
  59 DISPATCH_MALLOC DISPATCH_NOTHROW
  60 dispatch_semaphore_t
  61 dispatch_semaphore_create(long value);
  62
  63 /*!
  64  * @function dispatch_semaphore_wait
  65  *
  66  * @abstract
  67  * Wait (decrement) for a semaphore.
  68  *
  69  * @discussion
  70  * Decrement the counting semaphore. If the resulting value is less than zero,
  71  * this function waits in FIFO order for a signal to occur before returning.
  72  *
  73  * @param dsema
  74  * The semaphore. The result of passing NULL in this parameter is undefined.
  75  *
  76  * @param timeout
  77  * When to timeout (see dispatch_time). As a convenience, there are the
  78  * DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER constants.
  79  *
  80  * @result
  81  * Returns zero on success, or non-zero if the timeout occurred.
  82  */
  83 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_NA)
  84 DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
  85 long
  86 dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);
  87
  88 /*!
  89  * @function dispatch_semaphore_signal
  90  *
  91  * @abstract
  92  * Signal (increment) a semaphore.
  93  *
  94  * @discussion
  95  * Increment the counting semaphore. If the previous value was less than zero,
  96  * this function wakes a waiting thread before returning.
  97  *
  98  * @param dsema The counting semaphore.
  99  * The result of passing NULL in this parameter is undefined.
 100  *
 101  * @result
 102  * This function returns non-zero if a thread is woken. Otherwise, zero is
 103  * returned.
 104  */
 105 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_NA)
 106 DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
 107 long
 108 dispatch_semaphore_signal(dispatch_semaphore_t dsema);
 109
 110 __END_DECLS
 111
 112 #endif /* __DISPATCH_SEMAPHORE__ */