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prsem.h
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00001 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
00002 /* ***** BEGIN LICENSE BLOCK *****
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00010  * Software distributed under the License is distributed on an "AS IS" basis,
00011  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00012  * for the specific language governing rights and limitations under the
00013  * License.
00014  *
00015  * The Original Code is the Netscape Portable Runtime (NSPR).
00016  *
00017  * The Initial Developer of the Original Code is
00018  * Netscape Communications Corporation.
00019  * Portions created by the Initial Developer are Copyright (C) 1998-2000
00020  * the Initial Developer. All Rights Reserved.
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00022  * Contributor(s):
00023  *
00024  * Alternatively, the contents of this file may be used under the terms of
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00037 
00038 #ifndef prsem_h___
00039 #define prsem_h___
00040 
00041 /*
00042 ** API for counting semaphores. Semaphores are counting synchronizing 
00043 ** variables based on a lock and a condition variable.  They are lightweight 
00044 ** contention control for a given count of resources.
00045 */
00046 #include "prtypes.h"
00047 
00048 PR_BEGIN_EXTERN_C
00049 
00050 typedef struct PRSemaphore PRSemaphore;
00051 
00052 /*
00053 ** Create a new semaphore object.
00054 */
00055 NSPR_API(PRSemaphore*) PR_NewSem(PRUintn value);
00056 
00057 /*
00058 ** Destroy the given semaphore object.
00059 **
00060 */
00061 NSPR_API(void) PR_DestroySem(PRSemaphore *sem);
00062 
00063 /*
00064 ** Wait on a Semaphore.
00065 ** 
00066 ** This routine allows a calling thread to wait or proceed depending upon the 
00067 ** state of the semahore sem. The thread can proceed only if the counter value 
00068 ** of the semaphore sem is currently greater than 0. If the value of semaphore 
00069 ** sem is positive, it is decremented by one and the routine returns immediately 
00070 ** allowing the calling thread to continue. If the value of semaphore sem is 0, 
00071 ** the calling thread blocks awaiting the semaphore to be released by another 
00072 ** thread.
00073 ** 
00074 ** This routine can return PR_PENDING_INTERRUPT if the waiting thread 
00075 ** has been interrupted.
00076 */
00077 NSPR_API(PRStatus) PR_WaitSem(PRSemaphore *sem);
00078 
00079 /*
00080 ** This routine increments the counter value of the semaphore. If other threads 
00081 ** are blocked for the semaphore, then the scheduler will determine which ONE 
00082 ** thread will be unblocked.
00083 */
00084 NSPR_API(void) PR_PostSem(PRSemaphore *sem);
00085 
00086 /*
00087 ** Returns the value of the semaphore referenced by sem without affecting
00088 ** the state of the semaphore.  The value represents the semaphore vaule
00089 F** at the time of the call, but may not be the actual value when the
00090 ** caller inspects it.
00091 */
00092 NSPR_API(PRUintn) PR_GetValueSem(PRSemaphore *sem);
00093 
00094 PR_END_EXTERN_C
00095 
00096 #endif /* prsem_h___ */