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