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 /* -*- 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;

 }