michael@0: /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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: /*
michael@0:  *  os2cv.c -- OS/2 Machine-Dependent Code for Condition Variables
michael@0:  *
michael@0:  *  We implement our own condition variable wait queue.  Each thread
michael@0:  *  has a semaphore object (thread->md.blocked_sema) to block on while
michael@0:  *  waiting on a condition variable.
michael@0:  *
michael@0:  *  We use a deferred condition notify algorithm.  When PR_NotifyCondVar
michael@0:  *  or PR_NotifyAllCondVar is called, the condition notifies are simply
michael@0:  *  recorded in the _MDLock structure.  We defer the condition notifies
michael@0:  *  until right after we unlock the lock.  This way the awakened threads
michael@0:  *  have a better chance to reaquire the lock.
michael@0:  */
michael@0:  
michael@0: #include "primpl.h"
michael@0: 
michael@0: /*
michael@0:  * AddThreadToCVWaitQueueInternal --
michael@0:  *
michael@0:  * Add the thread to the end of the condition variable's wait queue.
michael@0:  * The CV's lock must be locked when this function is called.
michael@0:  */
michael@0: 
michael@0: static void
michael@0: AddThreadToCVWaitQueueInternal(PRThread *thred, struct _MDCVar *cv)
michael@0: {
michael@0:     PR_ASSERT((cv->waitTail != NULL && cv->waitHead != NULL)
michael@0:             || (cv->waitTail == NULL && cv->waitHead == NULL));
michael@0:     cv->nwait += 1;
michael@0:     thred->md.inCVWaitQueue = PR_TRUE;
michael@0:     thred->md.next = NULL;
michael@0:     thred->md.prev = cv->waitTail;
michael@0:     if (cv->waitHead == NULL) {
michael@0:         cv->waitHead = thred;
michael@0:     } else {
michael@0:         cv->waitTail->md.next = thred;
michael@0:     }
michael@0:     cv->waitTail = thred;
michael@0: }
michael@0: 
michael@0: /*
michael@0:  * md_UnlockAndPostNotifies --
michael@0:  *
michael@0:  * Unlock the lock, and then do the deferred condition notifies.
michael@0:  * If waitThred and waitCV are not NULL, waitThred is added to
michael@0:  * the wait queue of waitCV before the lock is unlocked.
michael@0:  *
michael@0:  * This function is called by _PR_MD_WAIT_CV and _PR_MD_UNLOCK,
michael@0:  * the two places where a lock is unlocked.
michael@0:  */
michael@0: void
michael@0: md_UnlockAndPostNotifies(
michael@0:     _MDLock *lock,
michael@0:     PRThread *waitThred,
michael@0:     _MDCVar *waitCV)
michael@0: {
michael@0:     PRIntn index;
michael@0:     _MDNotified post;
michael@0:     _MDNotified *notified, *prev = NULL;
michael@0: 
michael@0:     /*
michael@0:      * Time to actually notify any conditions that were affected
michael@0:      * while the lock was held.  Get a copy of the list that's in
michael@0:      * the lock structure and then zero the original.  If it's
michael@0:      * linked to other such structures, we own that storage.
michael@0:      */
michael@0:     post = lock->notified;  /* a safe copy; we own the lock */
michael@0: 
michael@0: #if defined(DEBUG)
michael@0:     memset(&lock->notified, 0, sizeof(_MDNotified));  /* reset */
michael@0: #else
michael@0:     lock->notified.length = 0;  /* these are really sufficient */
michael@0:     lock->notified.link = NULL;
michael@0: #endif
michael@0: 
michael@0:     /* 
michael@0:      * Figure out how many threads we need to wake up.
michael@0:      */
michael@0:     notified = &post;  /* this is where we start */
michael@0:     do {
michael@0:         for (index = 0; index < notified->length; ++index) {
michael@0:             _MDCVar *cv = notified->cv[index].cv;
michael@0:             PRThread *thred;
michael@0:             int i;
michael@0:             
michael@0:             /* Fast special case: no waiting threads */
michael@0:             if (cv->waitHead == NULL) {
michael@0:                 notified->cv[index].notifyHead = NULL;
michael@0:                 continue;
michael@0:             }
michael@0: 
michael@0:             /* General case */
michael@0:             if (-1 == notified->cv[index].times) {
michael@0:                 /* broadcast */
michael@0:                 thred = cv->waitHead;
michael@0:                 while (thred != NULL) {
michael@0:                     thred->md.inCVWaitQueue = PR_FALSE;
michael@0:                     thred = thred->md.next;
michael@0:                 }
michael@0:                 notified->cv[index].notifyHead = cv->waitHead;
michael@0:                 cv->waitHead = cv->waitTail = NULL;
michael@0:                 cv->nwait = 0;
michael@0:             } else {
michael@0:                 thred = cv->waitHead;
michael@0:                 i = notified->cv[index].times;
michael@0:                 while (thred != NULL && i > 0) {
michael@0:                     thred->md.inCVWaitQueue = PR_FALSE;
michael@0:                     thred = thred->md.next;
michael@0:                     i--;
michael@0:                 }
michael@0:                 notified->cv[index].notifyHead = cv->waitHead;
michael@0:                 cv->waitHead = thred;
michael@0:                 if (cv->waitHead == NULL) {
michael@0:                     cv->waitTail = NULL;
michael@0:                 } else {
michael@0:                     if (cv->waitHead->md.prev != NULL) {
michael@0:                         cv->waitHead->md.prev->md.next = NULL;
michael@0:                         cv->waitHead->md.prev = NULL;
michael@0:                     }
michael@0:                 }
michael@0:                 cv->nwait -= notified->cv[index].times - i;
michael@0:             }
michael@0:         }
michael@0:         notified = notified->link;
michael@0:     } while (NULL != notified);
michael@0: 
michael@0:     if (waitThred) {
michael@0:         AddThreadToCVWaitQueueInternal(waitThred, waitCV);
michael@0:     }
michael@0: 
michael@0:     /* Release the lock before notifying */
michael@0:     DosReleaseMutexSem(lock->mutex);
michael@0: 
michael@0:     notified = &post;  /* this is where we start */
michael@0:     do {
michael@0:         for (index = 0; index < notified->length; ++index) {
michael@0:             PRThread *thred;
michael@0:             PRThread *next;
michael@0: 
michael@0:             thred = notified->cv[index].notifyHead;
michael@0:             while (thred != NULL) {
michael@0:                 BOOL rv;
michael@0: 
michael@0:                 next = thred->md.next;
michael@0:                 thred->md.prev = thred->md.next = NULL;
michael@0:                 rv = DosPostEventSem(thred->md.blocked_sema);
michael@0:                 PR_ASSERT(rv == NO_ERROR);
michael@0:                 thred = next;
michael@0:             }
michael@0:         }
michael@0:         prev = notified;
michael@0:         notified = notified->link;
michael@0:         if (&post != prev) PR_DELETE(prev);
michael@0:     } while (NULL != notified);
michael@0: }
michael@0: 
michael@0: /*
michael@0:  * Notifies just get posted to the protecting mutex.  The
michael@0:  * actual notification is done when the lock is released so that
michael@0:  * MP systems don't contend for a lock that they can't have.
michael@0:  */
michael@0: static void md_PostNotifyToCvar(_MDCVar *cvar, _MDLock *lock,
michael@0:         PRBool broadcast)
michael@0: {
michael@0:     PRIntn index = 0;
michael@0:     _MDNotified *notified = &lock->notified;
michael@0: 
michael@0:     while (1) {
michael@0:         for (index = 0; index < notified->length; ++index) {
michael@0:             if (notified->cv[index].cv == cvar) {
michael@0:                 if (broadcast) {
michael@0:                     notified->cv[index].times = -1;
michael@0:                 } else if (-1 != notified->cv[index].times) {
michael@0:                     notified->cv[index].times += 1;
michael@0:                 }
michael@0:                 return;
michael@0:             }
michael@0:         }
michael@0:         /* if not full, enter new CV in this array */
michael@0:         if (notified->length < _MD_CV_NOTIFIED_LENGTH) break;
michael@0: 
michael@0:         /* if there's no link, create an empty array and link it */
michael@0:         if (NULL == notified->link) {
michael@0:             notified->link = PR_NEWZAP(_MDNotified);
michael@0:         }
michael@0: 
michael@0:         notified = notified->link;
michael@0:     }
michael@0: 
michael@0:     /* A brand new entry in the array */
michael@0:     notified->cv[index].times = (broadcast) ? -1 : 1;
michael@0:     notified->cv[index].cv = cvar;
michael@0:     notified->length += 1;
michael@0: }
michael@0: 
michael@0: /*
michael@0:  * _PR_MD_NEW_CV() -- Creating new condition variable
michael@0:  * ... Solaris uses cond_init() in similar function.
michael@0:  *
michael@0:  * returns: -1 on failure
michael@0:  *          0 when it succeeds.
michael@0:  *
michael@0:  */
michael@0: PRInt32
michael@0: _PR_MD_NEW_CV(_MDCVar *cv)
michael@0: {
michael@0:     cv->magic = _MD_MAGIC_CV;
michael@0:     /*
michael@0:      * The waitHead, waitTail, and nwait fields are zeroed
michael@0:      * when the PRCondVar structure is created.
michael@0:      */
michael@0:     return 0;
michael@0: } 
michael@0: 
michael@0: void _PR_MD_FREE_CV(_MDCVar *cv)
michael@0: {
michael@0:     cv->magic = (PRUint32)-1;
michael@0:     return;
michael@0: }
michael@0: 
michael@0: /*
michael@0:  *  _PR_MD_WAIT_CV() -- Wait on condition variable
michael@0:  */
michael@0: void
michael@0: _PR_MD_WAIT_CV(_MDCVar *cv, _MDLock *lock, PRIntervalTime timeout )
michael@0: {
michael@0:     PRThread *thred = _PR_MD_CURRENT_THREAD();
michael@0:     ULONG rv, count;
michael@0:     ULONG msecs = (timeout == PR_INTERVAL_NO_TIMEOUT) ?
michael@0:             SEM_INDEFINITE_WAIT : PR_IntervalToMilliseconds(timeout);
michael@0: 
michael@0:     /*
michael@0:      * If we have pending notifies, post them now.
michael@0:      */
michael@0:     if (0 != lock->notified.length) {
michael@0:         md_UnlockAndPostNotifies(lock, thred, cv);
michael@0:     } else {
michael@0:         AddThreadToCVWaitQueueInternal(thred, cv);
michael@0:         DosReleaseMutexSem(lock->mutex); 
michael@0:     }
michael@0: 
michael@0:     /* Wait for notification or timeout; don't really care which */
michael@0:     rv = DosWaitEventSem(thred->md.blocked_sema, msecs);
michael@0:     if (rv == NO_ERROR) {
michael@0:         DosResetEventSem(thred->md.blocked_sema, &count);
michael@0:     }
michael@0: 
michael@0:     DosRequestMutexSem((lock->mutex), SEM_INDEFINITE_WAIT);
michael@0: 
michael@0:     PR_ASSERT(rv == NO_ERROR || rv == ERROR_TIMEOUT);
michael@0: 
michael@0:     if(rv == ERROR_TIMEOUT)
michael@0:     {
michael@0:        if (thred->md.inCVWaitQueue) {
michael@0:            PR_ASSERT((cv->waitTail != NULL && cv->waitHead != NULL)
michael@0:                    || (cv->waitTail == NULL && cv->waitHead == NULL));
michael@0:            cv->nwait -= 1;
michael@0:            thred->md.inCVWaitQueue = PR_FALSE;
michael@0:            if (cv->waitHead == thred) {
michael@0:                cv->waitHead = thred->md.next;
michael@0:                if (cv->waitHead == NULL) {
michael@0:                    cv->waitTail = NULL;
michael@0:                } else {
michael@0:                    cv->waitHead->md.prev = NULL;
michael@0:                }
michael@0:            } else {
michael@0:                PR_ASSERT(thred->md.prev != NULL);
michael@0:                thred->md.prev->md.next = thred->md.next;
michael@0:                if (thred->md.next != NULL) {
michael@0:                    thred->md.next->md.prev = thred->md.prev;
michael@0:                } else {
michael@0:                    PR_ASSERT(cv->waitTail == thred);
michael@0:                    cv->waitTail = thred->md.prev;
michael@0:                }
michael@0:            }
michael@0:            thred->md.next = thred->md.prev = NULL;
michael@0:        } else {
michael@0:            /*
michael@0:             * This thread must have been notified, but the
michael@0:             * SemRelease call happens after SemRequest
michael@0:             * times out.  Wait on the semaphore again to make it
michael@0:             * non-signaled.  We assume this wait won't take long.
michael@0:             */
michael@0:            rv = DosWaitEventSem(thred->md.blocked_sema, SEM_INDEFINITE_WAIT);
michael@0:            if (rv == NO_ERROR) {
michael@0:                DosResetEventSem(thred->md.blocked_sema, &count);
michael@0:            }
michael@0:            PR_ASSERT(rv == NO_ERROR);
michael@0:        }
michael@0:     }
michael@0:     PR_ASSERT(thred->md.inCVWaitQueue == PR_FALSE);
michael@0:     return;
michael@0: } /* --- end _PR_MD_WAIT_CV() --- */
michael@0: 
michael@0: void
michael@0: _PR_MD_NOTIFY_CV(_MDCVar *cv, _MDLock *lock)
michael@0: {
michael@0:     md_PostNotifyToCvar(cv, lock, PR_FALSE);
michael@0:     return;
michael@0: }
michael@0: 
michael@0: PRStatus
michael@0: _PR_MD_NEW_LOCK(_MDLock *lock)
michael@0: {
michael@0:     DosCreateMutexSem(0, &(lock->mutex), 0, 0);
michael@0:     (lock)->notified.length=0;
michael@0:     (lock)->notified.link=NULL;
michael@0:     return PR_SUCCESS;
michael@0: }
michael@0: 
michael@0: void
michael@0: _PR_MD_NOTIFYALL_CV(_MDCVar *cv, _MDLock *lock)
michael@0: {
michael@0:     md_PostNotifyToCvar(cv, lock, PR_TRUE);
michael@0:     return;
michael@0: }
michael@0: 
michael@0: void _PR_MD_UNLOCK(_MDLock *lock)
michael@0: {
michael@0:     if (0 != lock->notified.length) {
michael@0:         md_UnlockAndPostNotifies(lock, NULL, NULL);
michael@0:     } else {
michael@0:         DosReleaseMutexSem(lock->mutex);
michael@0:     }
michael@0: }