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/*
* The contents of this file are subject to the AOLserver Public License
* Version 1.1 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://aolserver.com/.
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is AOLserver Code and related documentation
* distributed by AOL.
*
* The Initial Developer of the Original Code is America Online,
* Inc. Portions created by AOL are Copyright (C) 1999 America Online,
* Inc. All Rights Reserved.
*
* Alternatively, the contents of this file may be used under the terms
* of the GNU General Public License (the "GPL"), in which case the
* provisions of GPL are applicable instead of those above. If you wish
* to allow use of your version of this file only under the terms of the
* GPL and not to allow others to use your version of this file under the
* License, indicate your decision by deleting the provisions above and
* replace them with the notice and other provisions required by the GPL.
* If you do not delete the provisions above, a recipient may use your
* version of this file under either the License or the GPL.
*/
/*
* sema.c --
*
* Couting semaphore routines. Semaphores differ from ordinary mutex
* locks in that they maintain a count instead of a simple locked/unlocked
* state. Threads block if the semaphore count is less than one.
*
* Note: Semaphores are almost always a bad idea. In general, cleaner
* and more flexible code can be implemented with condition variables
* instead. Indeed, the semaphores below are implmented using
* condition variables indicating that condition variables are the
* more fundamental synchronization object.
*/
static const char *RCSID = "@(#) $Header: /cvsroot/aolserver/aolserver/thread/sema.c,v 1.4 2000/11/06 17:53:50 jgdavidson Exp $, compiled: " __DATE__ " " __TIME__;
#include "thread.h"
/*
* The following structure defines a counting semaphore using a lock
* and condition.
*/
typedef struct {
Ns_Mutex lock;
Ns_Cond cond;
int count;
} Sema;
/*
*----------------------------------------------------------------------
*
* Ns_SemaInit --
*
* Initialize a semaphore. Note that because semaphores are
* initialized with a starting count they cannot be automatically
* created on first use as with other synchronization objects.
*
* Results:
* None.
*
* Side effects:
* Memory is allocated and initialized from the heap.
*
*----------------------------------------------------------------------
*/
void
Ns_SemaInit(Ns_Sema *semaPtr, int initCount)
{
Sema *sPtr;
sPtr = NsAlloc(sizeof(Sema));
sPtr->count = initCount;
Ns_MutexInit2(&sPtr->lock, "nsthread:sema");
Ns_CondInit(&sPtr->cond);
*semaPtr = (Ns_Sema) sPtr;
}
/*
*----------------------------------------------------------------------
*
* Ns_SemaDestroy --
*
* Destroy a semaphore. This routine should almost never be used
* as synchronization objects are normally created at process startup
* and exist entirely in process memory until the process exits.
*
* Results:
* None.
*
* Side effects:
* Memory is returned to the heap.
*
*----------------------------------------------------------------------
*/
void
Ns_SemaDestroy(Ns_Sema *semaPtr)
{
if (*semaPtr != NULL) {
Sema *sPtr = (Sema *) *semaPtr;
Ns_MutexDestroy(&sPtr->lock);
Ns_CondDestroy(&sPtr->cond);
NsFree(sPtr);
*semaPtr = NULL;
}
}
/*
*----------------------------------------------------------------------
*
* Ns_SemaWait --
*
* Wait for a semaphore count to be greater than zero.
*
* Results:
* None.
*
* Side effects:
* Calling thread may wait on the condition.
*
*----------------------------------------------------------------------
*/
void
Ns_SemaWait(Ns_Sema *semaPtr)
{
Sema *sPtr = (Sema *) *semaPtr;
Ns_MutexLock(&sPtr->lock);
while (sPtr->count == 0) {
Ns_CondWait(&sPtr->cond, &sPtr->lock);
}
sPtr->count--;
Ns_MutexUnlock(&sPtr->lock);
}
/*
*----------------------------------------------------------------------
*
* Ns_SemaPost --
*
* Increment a semaphore count, releasing waiting threads if needed.
*
* Results:
* None.
*
* Side effects:
* Threads waiting on the condition, if any, may be resumed.
*
*----------------------------------------------------------------------
*/
void
Ns_SemaPost(Ns_Sema *semaPtr, int count)
{
Sema *sPtr = (Sema *) *semaPtr;
Ns_MutexLock(&sPtr->lock);
sPtr->count += count;
if (count == 1) {
Ns_CondSignal(&sPtr->cond);
} else {
Ns_CondBroadcast(&sPtr->cond);
}
Ns_MutexUnlock(&sPtr->lock);
}
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