The Tor Browser: nsprpub/pr/src/threads/prsem.c@ca08bd8f51b2

     1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* This Source Code Form is subject to the terms of the Mozilla Public

     3  * License, v. 2.0. If a copy of the MPL was not distributed with this

     4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     6 #include "primpl.h"

     7 #include "obsolete/prsem.h"

     9 /************************************************************************/

    11 /*

    12 ** Create a new semaphore.

    13 */

    14 PR_IMPLEMENT(PRSemaphore*) PR_NewSem(PRUintn value)

    15 {

    16     PRSemaphore *sem;

    17     PRCondVar *cvar;

    18     PRLock *lock;

    20     sem = PR_NEWZAP(PRSemaphore);

    21     if (sem) {

    22 #ifdef HAVE_CVAR_BUILT_ON_SEM

    23         _PR_MD_NEW_SEM(&sem->md, value);

    24 #else

    25         lock = PR_NewLock();

    26         if (!lock) {

    27             PR_DELETE(sem);

    28             return NULL;

    29     	}

    31         cvar = PR_NewCondVar(lock);

    32         if (!cvar) {

    33             PR_DestroyLock(lock);

    34             PR_DELETE(sem);

    35             return NULL;

    36     	}

    37     	sem->cvar = cvar;

    38     	sem->count = value;

    39 #endif

    40     }

    41     return sem;

    42 }

    44 /*

    45 ** Destroy a semaphore. There must be no thread waiting on the semaphore.

    46 ** The caller is responsible for guaranteeing that the semaphore is

    47 ** no longer in use.

    48 */

    49 PR_IMPLEMENT(void) PR_DestroySem(PRSemaphore *sem)

    50 {

    51 #ifdef HAVE_CVAR_BUILT_ON_SEM

    52     _PR_MD_DESTROY_SEM(&sem->md);

    53 #else

    54     PR_ASSERT(sem->waiters == 0);

    56     PR_DestroyLock(sem->cvar->lock);

    57     PR_DestroyCondVar(sem->cvar);

    58 #endif

    59     PR_DELETE(sem);

    60 }

    62 /*

    63 ** Wait on a Semaphore.

    64 **

    65 ** This routine allows a calling thread to wait or proceed depending upon the

    66 ** state of the semahore sem. The thread can proceed only if the counter value

    67 ** of the semaphore sem is currently greater than 0. If the value of semaphore

    68 ** sem is positive, it is decremented by one and the routine returns immediately

    69 ** allowing the calling thread to continue. If the value of semaphore sem is 0,

    70 ** the calling thread blocks awaiting the semaphore to be released by another

    71 ** thread.

    72 **

    73 ** This routine can return PR_PENDING_INTERRUPT if the waiting thread

    74 ** has been interrupted.

    75 */

    76 PR_IMPLEMENT(PRStatus) PR_WaitSem(PRSemaphore *sem)

    77 {

    78 	PRStatus status = PR_SUCCESS;

    80 #ifdef HAVE_CVAR_BUILT_ON_SEM

    81 	return _PR_MD_WAIT_SEM(&sem->md);

    82 #else

    83 	PR_Lock(sem->cvar->lock);

    84 	while (sem->count == 0) {

    85 		sem->waiters++;

    86 		status = PR_WaitCondVar(sem->cvar, PR_INTERVAL_NO_TIMEOUT);

    87 		sem->waiters--;

    88 		if (status != PR_SUCCESS)

    89 			break;

    90 	}

    91 	if (status == PR_SUCCESS)

    92 		sem->count--;

    93 	PR_Unlock(sem->cvar->lock);

    94 #endif

    96 	return (status);

    97 }

    99 /*

   100 ** This routine increments the counter value of the semaphore. If other threads

   101 ** are blocked for the semaphore, then the scheduler will determine which ONE

   102 ** thread will be unblocked.

   103 */

   104 PR_IMPLEMENT(void) PR_PostSem(PRSemaphore *sem)

   105 {

   106 #ifdef HAVE_CVAR_BUILT_ON_SEM

   107 	_PR_MD_POST_SEM(&sem->md);

   108 #else

   109 	PR_Lock(sem->cvar->lock);

   110 	if (sem->waiters)

   111 		PR_NotifyCondVar(sem->cvar);

   112 	sem->count++;

   113 	PR_Unlock(sem->cvar->lock);

   114 #endif

   115 }

   117 #if DEBUG

   118 /*

   119 ** Returns the value of the semaphore referenced by sem without affecting

   120 ** the state of the semaphore.  The value represents the semaphore vaule

   121 ** at the time of the call, but may not be the actual value when the

   122 ** caller inspects it. (FOR DEBUGGING ONLY)

   123 */

   124 PR_IMPLEMENT(PRUintn) PR_GetValueSem(PRSemaphore *sem)

   125 {

   126 	PRUintn rv;

   128 #ifdef HAVE_CVAR_BUILT_ON_SEM

   129 	rv = _PR_MD_GET_VALUE_SEM(&sem->md);

   130 #else

   131 	PR_Lock(sem->cvar->lock);

   132 	rv = sem->count;

   133 	PR_Unlock(sem->cvar->lock);

   134 #endif

   136 	return rv;

   137 }

   138 #endif

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