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prsem.c
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00001 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
00002 /* ***** BEGIN LICENSE BLOCK *****
00003  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00004  *
00005  * The contents of this file are subject to the Mozilla Public License Version
00006  * 1.1 (the "License"); you may not use this file except in compliance with
00007  * the License. You may obtain a copy of the License at
00008  * http://www.mozilla.org/MPL/
00009  *
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.
00021  *
00022  * Contributor(s):
00023  *
00024  * Alternatively, the contents of this file may be used under the terms of
00025  * either the GNU General Public License Version 2 or later (the "GPL"), or
00026  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00027  * in which case the provisions of the GPL or the LGPL are applicable instead
00028  * of those above. If you wish to allow use of your version of this file only
00029  * under the terms of either the GPL or the LGPL, and not to allow others to
00030  * use your version of this file under the terms of the MPL, indicate your
00031  * decision by deleting the provisions above and replace them with the notice
00032  * and other provisions required by the GPL or the LGPL. If you do not delete
00033  * the provisions above, a recipient may use your version of this file under
00034  * the terms of any one of the MPL, the GPL or the LGPL.
00035  *
00036  * ***** END LICENSE BLOCK ***** */
00037 
00038 #include "primpl.h"
00039 #if defined(XP_MAC)
00040 #include "prsem.h"
00041 #else
00042 #include "obsolete/prsem.h"
00043 #endif
00044 
00045 /************************************************************************/
00046 
00047 /*
00048 ** Create a new semaphore.
00049 */
00050 PR_IMPLEMENT(PRSemaphore*) PR_NewSem(PRUintn value)
00051 {
00052     PRSemaphore *sem;
00053     PRCondVar *cvar;
00054     PRLock *lock;
00055 
00056     sem = PR_NEWZAP(PRSemaphore);
00057     if (sem) {
00058 #ifdef HAVE_CVAR_BUILT_ON_SEM
00059         _PR_MD_NEW_SEM(&sem->md, value);
00060 #else
00061         lock = PR_NewLock();
00062         if (!lock) {
00063             PR_DELETE(sem);
00064             return NULL;
00065        }
00066 
00067         cvar = PR_NewCondVar(lock);
00068         if (!cvar) {
00069             PR_DestroyLock(lock);
00070             PR_DELETE(sem);
00071             return NULL;
00072        }
00073        sem->cvar = cvar;
00074        sem->count = value;
00075 #endif
00076     }
00077     return sem;
00078 }
00079 
00080 /*
00081 ** Destroy a semaphore. There must be no thread waiting on the semaphore.
00082 ** The caller is responsible for guaranteeing that the semaphore is
00083 ** no longer in use.
00084 */
00085 PR_IMPLEMENT(void) PR_DestroySem(PRSemaphore *sem)
00086 {
00087 #ifdef HAVE_CVAR_BUILT_ON_SEM
00088     _PR_MD_DESTROY_SEM(&sem->md);
00089 #else
00090     PR_ASSERT(sem->waiters == 0);
00091 
00092     PR_DestroyLock(sem->cvar->lock);
00093     PR_DestroyCondVar(sem->cvar);
00094 #endif
00095     PR_DELETE(sem);
00096 }
00097 
00098 /*
00099 ** Wait on a Semaphore.
00100 ** 
00101 ** This routine allows a calling thread to wait or proceed depending upon the 
00102 ** state of the semahore sem. The thread can proceed only if the counter value 
00103 ** of the semaphore sem is currently greater than 0. If the value of semaphore 
00104 ** sem is positive, it is decremented by one and the routine returns immediately 
00105 ** allowing the calling thread to continue. If the value of semaphore sem is 0, 
00106 ** the calling thread blocks awaiting the semaphore to be released by another 
00107 ** thread.
00108 ** 
00109 ** This routine can return PR_PENDING_INTERRUPT if the waiting thread 
00110 ** has been interrupted.
00111 */
00112 PR_IMPLEMENT(PRStatus) PR_WaitSem(PRSemaphore *sem)
00113 {
00114        PRStatus status = PR_SUCCESS;
00115 
00116 #ifdef HAVE_CVAR_BUILT_ON_SEM
00117        return _PR_MD_WAIT_SEM(&sem->md);
00118 #else
00119        PR_Lock(sem->cvar->lock);
00120        while (sem->count == 0) {
00121               sem->waiters++;
00122               status = PR_WaitCondVar(sem->cvar, PR_INTERVAL_NO_TIMEOUT);
00123               sem->waiters--;
00124               if (status != PR_SUCCESS)
00125                      break;
00126        }
00127        if (status == PR_SUCCESS)
00128               sem->count--;
00129        PR_Unlock(sem->cvar->lock);
00130 #endif
00131        
00132        return (status);
00133 }
00134 
00135 /*
00136 ** This routine increments the counter value of the semaphore. If other threads 
00137 ** are blocked for the semaphore, then the scheduler will determine which ONE 
00138 ** thread will be unblocked.
00139 */
00140 PR_IMPLEMENT(void) PR_PostSem(PRSemaphore *sem)
00141 {
00142 #ifdef HAVE_CVAR_BUILT_ON_SEM
00143        _PR_MD_POST_SEM(&sem->md);
00144 #else
00145        PR_Lock(sem->cvar->lock);
00146        if (sem->waiters)
00147               PR_NotifyCondVar(sem->cvar);
00148        sem->count++;
00149        PR_Unlock(sem->cvar->lock);
00150 #endif
00151 }
00152 
00153 #if DEBUG
00154 /*
00155 ** Returns the value of the semaphore referenced by sem without affecting
00156 ** the state of the semaphore.  The value represents the semaphore vaule
00157 ** at the time of the call, but may not be the actual value when the
00158 ** caller inspects it. (FOR DEBUGGING ONLY)
00159 */
00160 PR_IMPLEMENT(PRUintn) PR_GetValueSem(PRSemaphore *sem)
00161 {
00162        PRUintn rv;
00163 
00164 #ifdef HAVE_CVAR_BUILT_ON_SEM
00165        rv = _PR_MD_GET_VALUE_SEM(&sem->md);
00166 #else
00167        PR_Lock(sem->cvar->lock);
00168        rv = sem->count;
00169        PR_Unlock(sem->cvar->lock);
00170 #endif
00171        
00172        return rv;
00173 }
00174 #endif