The Tor Browser: nsprpub/pr/src/bthreads/btcvar.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/bthreads/btcvar.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/bthreads/btcvar.c

Wed, 31 Dec 2014 06:55:46 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:55:46 +0100
changeset 1: ca08bd8f51b2
permissions: -rw-r--r--

Added tag TORBROWSER_REPLICA for changeset 6474c204b198

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include <kernel/OS.h>
 #include "primpl.h"
 /*
 ** Create a new condition variable.
 **
 ** 	"lock" is the lock used to protect the condition variable.
 **
 ** Condition variables are synchronization objects that threads can use
 ** to wait for some condition to occur.
 **
 ** This may fail if memory is tight or if some operating system resource
 ** is low. In such cases, a NULL will be returned.
 */
 PR_IMPLEMENT(PRCondVar*)
     PR_NewCondVar (PRLock *lock)
 {
     PRCondVar *cv = PR_NEW( PRCondVar );
     PR_ASSERT( NULL != lock );
     if( NULL != cv )
     {
 	cv->lock = lock;
 	cv->sem = create_sem(0, "CVSem");
 	cv->handshakeSem = create_sem(0, "CVHandshake");
 	cv->signalSem = create_sem( 0, "CVSignal");
 	cv->signalBenCount = 0;
 	cv->ns = cv->nw = 0;
 	PR_ASSERT( cv->sem >= B_NO_ERROR );
 	PR_ASSERT( cv->handshakeSem >= B_NO_ERROR );
 	PR_ASSERT( cv->signalSem >= B_NO_ERROR );
     }
     return cv;
 } /* PR_NewCondVar */
 /*
 ** Destroy a condition variable. There must be no thread
 ** waiting on the condvar. The caller is responsible for guaranteeing
 ** that the condvar is no longer in use.
 **
 */
 PR_IMPLEMENT(void)
     PR_DestroyCondVar (PRCondVar *cvar)
 {
     status_t result = delete_sem( cvar->sem );
     PR_ASSERT( result == B_NO_ERROR );
     result = delete_sem( cvar->handshakeSem );
     PR_ASSERT( result == B_NO_ERROR );
     result = delete_sem( cvar->signalSem );
     PR_ASSERT( result == B_NO_ERROR );
     PR_DELETE( cvar );
 }
 /*
 ** The thread that waits on a condition is blocked in a "waiting on
 ** condition" state until another thread notifies the condition or a
 ** caller specified amount of time expires. The lock associated with
 ** the condition variable will be released, which must have be held
 ** prior to the call to wait.
 **
 ** Logically a notified thread is moved from the "waiting on condition"
 ** state and made "ready." When scheduled, it will attempt to reacquire
 ** the lock that it held when wait was called.
 **
 ** The timeout has two well known values, PR_INTERVAL_NO_TIMEOUT and
 ** PR_INTERVAL_NO_WAIT. The former value requires that a condition be
 ** notified (or the thread interrupted) before it will resume from the
 ** wait. If the timeout has a value of PR_INTERVAL_NO_WAIT, the effect
 ** is to release the lock, possibly causing a rescheduling within the
 ** runtime, then immediately attempting to reacquire the lock and resume.
 **
 ** Any other value for timeout will cause the thread to be rescheduled
 ** either due to explicit notification or an expired interval. The latter
 ** must be determined by treating time as one part of the monitored data
 ** being protected by the lock and tested explicitly for an expired
 ** interval.
 **
 ** Returns PR_FAILURE if the caller has not locked the lock associated
 ** with the condition variable or the thread was interrupted (PR_Interrupt()).
 ** The particular reason can be extracted with PR_GetError().
 */
 PR_IMPLEMENT(PRStatus)
     PR_WaitCondVar (PRCondVar *cvar, PRIntervalTime timeout)
 {
     status_t err;
     if( timeout == PR_INTERVAL_NO_WAIT )
     {
         PR_Unlock( cvar->lock );
         PR_Lock( cvar->lock );
         return PR_SUCCESS;
     }
     if( atomic_add( &cvar->signalBenCount, 1 ) > 0 )
     {
         if (acquire_sem(cvar->signalSem) == B_INTERRUPTED)
         {
             atomic_add( &cvar->signalBenCount, -1 );
             return PR_FAILURE;
         }
     }
     cvar->nw += 1;
     if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
     {
         release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
     }
     PR_Unlock( cvar->lock );
     if( timeout==PR_INTERVAL_NO_TIMEOUT )
     {
     	err = acquire_sem(cvar->sem);
     }
     else
     {
     	err = acquire_sem_etc(cvar->sem, 1, B_RELATIVE_TIMEOUT, PR_IntervalToMicroseconds(timeout) );
     }
     if( atomic_add( &cvar->signalBenCount, 1 ) > 0 )
     {
         while (acquire_sem(cvar->signalSem) == B_INTERRUPTED);
     }
     if (cvar->ns > 0)
     {
         release_sem_etc(cvar->handshakeSem, 1, B_DO_NOT_RESCHEDULE);
         cvar->ns -= 1;
     }
     cvar->nw -= 1;
     if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
     {
         release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
     }
     PR_Lock( cvar->lock );
     if(err!=B_NO_ERROR)
     {
         return PR_FAILURE;
     }
     return PR_SUCCESS;
 }
 /*
 ** Notify ONE thread that is currently waiting on 'cvar'. Which thread is
 ** dependent on the implementation of the runtime. Common sense would dictate
 ** that all threads waiting on a single condition have identical semantics,
 ** therefore which one gets notified is not significant.
 **
 ** The calling thead must hold the lock that protects the condition, as
 ** well as the invariants that are tightly bound to the condition, when
 ** notify is called.
 **
 ** Returns PR_FAILURE if the caller has not locked the lock associated
 ** with the condition variable.
 */
 PR_IMPLEMENT(PRStatus)
     PR_NotifyCondVar (PRCondVar *cvar)
 {
     status_t err ;
     if( atomic_add( &cvar->signalBenCount, 1 ) > 0 )
     {
         if (acquire_sem(cvar->signalSem) == B_INTERRUPTED)
         {
             atomic_add( &cvar->signalBenCount, -1 );
             return PR_FAILURE;
         }
     }
     if (cvar->nw > cvar->ns)
     {
         cvar->ns += 1;
         release_sem_etc(cvar->sem, 1, B_DO_NOT_RESCHEDULE);
         if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
         {
             release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
         }
         while (acquire_sem(cvar->handshakeSem) == B_INTERRUPTED)
         {
             err = B_INTERRUPTED;
         }
     }
     else
     {
         if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
         {
             release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
         }
     }
     return PR_SUCCESS;
 }
 /*
 ** Notify all of the threads waiting on the condition variable. The order
 ** that the threads are notified is indeterminant. The lock that protects
 ** the condition must be held.
 **
 ** Returns PR_FAILURE if the caller has not locked the lock associated
 ** with the condition variable.
 */
 PR_IMPLEMENT(PRStatus)
     PR_NotifyAllCondVar (PRCondVar *cvar)
 {
     int32 handshakes;
     status_t err = B_OK;
     if( atomic_add( &cvar->signalBenCount, 1 ) > 0 )
     {
         if (acquire_sem(cvar->signalSem) == B_INTERRUPTED)
         {
             atomic_add( &cvar->signalBenCount, -1 );
             return PR_FAILURE;
         }
     }
     if (cvar->nw > cvar->ns)
     {
         handshakes = cvar->nw - cvar->ns;
         cvar->ns = cvar->nw;
         release_sem_etc(cvar->sem, handshakes, B_DO_NOT_RESCHEDULE);
         if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
         {
             release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
         }
         while (acquire_sem_etc(cvar->handshakeSem, handshakes, 0, 0) == B_INTERRUPTED)
         {
             err = B_INTERRUPTED;
         }
     }
     else
     {
         if( atomic_add( &cvar->signalBenCount, -1 ) > 1 )
         {
             release_sem_etc(cvar->signalSem, 1, B_DO_NOT_RESCHEDULE);
         }
     }
     return PR_SUCCESS;
 }

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nsprpub/pr/src/bthreads/btcvar.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/bthreads/btcvar.c