threads/combined/prulock.c

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 "primpl.h"

#if defined(WIN95)
/*
** Some local variables report warnings on Win95 because the code paths
** using them are conditioned on HAVE_CUSTOME_USER_THREADS.
** The pragma suppresses the warning.
**
*/
#pragma warning(disable : 4101)
#endif


void _PR_InitLocks(void)
{
    _PR_MD_INIT_LOCKS();
}

/*
** Deal with delayed interrupts/requested reschedule during interrupt
** re-enables.
*/
void _PR_IntsOn(_PRCPU *cpu)
{
    PRUintn missed, pri, i;
    _PRInterruptTable *it;
    PRThread *me;

    PR_ASSERT(cpu);   /* Global threads don't have CPUs */
    PR_ASSERT(_PR_MD_GET_INTSOFF() > 0);
    me = _PR_MD_CURRENT_THREAD();
    PR_ASSERT(!(me->flags & _PR_IDLE_THREAD));

    /*
    ** Process delayed interrupts. This logic is kinda scary because we
    ** need to avoid losing an interrupt (it's ok to delay an interrupt
    ** until later).
    **
    ** There are two missed state words. _pr_ints.where indicates to the
    ** interrupt handler which state word is currently safe for
    ** modification.
    **
    ** This code scans both interrupt state words, using the where flag
    ** to indicate to the interrupt which state word is safe for writing.
    ** If an interrupt comes in during a scan the other word will be
    ** modified. This modification will be noticed during the next
    ** iteration of the loop or during the next call to this routine.
    */
    for (i = 0; i < 2; i++) {
        cpu->where = (1 - i);
        missed = cpu->u.missed[i];
        if (missed != 0) {
            cpu->u.missed[i] = 0;
            for (it = _pr_interruptTable; it->name; it++) {
                if (missed & it->missed_bit) {
                    PR_LOG(_pr_sched_lm, PR_LOG_MIN,
                           ("IntsOn[0]: %s intr", it->name));
                    (*it->handler)();
                }
            }
        }
    }

    if (cpu->u.missed[3] != 0) {
        _PRCPU *cpu;

        _PR_THREAD_LOCK(me);
        me->state = _PR_RUNNABLE;
        pri = me->priority;

        cpu = me->cpu;
        _PR_RUNQ_LOCK(cpu);
        _PR_ADD_RUNQ(me, cpu, pri);
        _PR_RUNQ_UNLOCK(cpu);
        _PR_THREAD_UNLOCK(me);
        _PR_MD_SWITCH_CONTEXT(me);
    }
}

/*
** Unblock the first runnable waiting thread. Skip over
** threads that are trying to be suspended
** Note: Caller must hold _PR_LOCK_LOCK()
*/
void _PR_UnblockLockWaiter(PRLock *lock)
{
    PRThread *t = NULL;
    PRThread *me;
    PRCList *q;

    q = lock->waitQ.next;
    PR_ASSERT(q != &lock->waitQ);
    while (q != &lock->waitQ) {
        /* Unblock first waiter */
        t = _PR_THREAD_CONDQ_PTR(q);

        /*
        ** We are about to change the thread's state to runnable and for local
        ** threads, we are going to assign a cpu to it.  So, protect thread's
        ** data structure.
        */
        _PR_THREAD_LOCK(t);

        if (t->flags & _PR_SUSPENDING) {
            q = q->next;
            _PR_THREAD_UNLOCK(t);
            continue;
        }

        /* Found a runnable thread */
        PR_ASSERT(t->state == _PR_LOCK_WAIT);
        PR_ASSERT(t->wait.lock == lock);
        t->wait.lock = 0;
        PR_REMOVE_LINK(&t->waitQLinks);         /* take it off lock's waitQ */

        /*
        ** If this is a native thread, nothing else to do except to wake it
        ** up by calling the machine dependent wakeup routine.
        **
        ** If this is a local thread, we need to assign it a cpu and
        ** put the thread on that cpu's run queue.  There are two cases to
        ** take care of.  If the currently running thread is also a local
        ** thread, we just assign our own cpu to that thread and put it on
        ** the cpu's run queue.  If the the currently running thread is a
        ** native thread, we assign the primordial cpu to it (on NT,
        ** MD_WAKEUP handles the cpu assignment).
        */

        if ( !_PR_IS_NATIVE_THREAD(t) ) {

            t->state = _PR_RUNNABLE;

            me = _PR_MD_CURRENT_THREAD();

            _PR_AddThreadToRunQ(me, t);
            _PR_THREAD_UNLOCK(t);
        } else {
            t->state = _PR_RUNNING;
            _PR_THREAD_UNLOCK(t);
        }
        _PR_MD_WAKEUP_WAITER(t);
        break;
    }
    return;
}

/************************************************************************/


PR_IMPLEMENT(PRLock*) PR_NewLock(void)
{
    PRLock *lock;

    if (!_pr_initialized) {
        _PR_ImplicitInitialization();
    }

    lock = PR_NEWZAP(PRLock);
    if (lock) {
        if (_PR_InitLock(lock) != PR_SUCCESS) {
            PR_DELETE(lock);
            return NULL;
        }
    }
    return lock;
}

PRStatus _PR_InitLock(PRLock *lock)
{
    if (_PR_MD_NEW_LOCK(&lock->ilock) != PR_SUCCESS) {
        return PR_FAILURE;
    }
    PR_INIT_CLIST(&lock->links);
    PR_INIT_CLIST(&lock->waitQ);
    return PR_SUCCESS;
}

/*
** Destroy the given lock "lock". There is no point in making this race
** free because if some other thread has the pointer to this lock all
** bets are off.
*/
PR_IMPLEMENT(void) PR_DestroyLock(PRLock *lock)
{
    _PR_FreeLock(lock);
    PR_DELETE(lock);
}

void _PR_FreeLock(PRLock *lock)
{
    PR_ASSERT(lock->owner == 0);
    _PR_MD_FREE_LOCK(&lock->ilock);
}

extern PRThread *suspendAllThread;
/*
** Lock the lock.
*/
PR_IMPLEMENT(void) PR_Lock(PRLock *lock)
{
    PRThread *me = _PR_MD_CURRENT_THREAD();
    PRIntn is;
    PRThread *t;
    PRCList *q;

    PR_ASSERT(me != suspendAllThread);
    PR_ASSERT(!(me->flags & _PR_IDLE_THREAD));
    PR_ASSERT(lock != NULL);
#ifdef _PR_GLOBAL_THREADS_ONLY
    _PR_MD_LOCK(&lock->ilock);
    PR_ASSERT(lock->owner == 0);
    lock->owner = me;
    return;
#else  /* _PR_GLOBAL_THREADS_ONLY */

    if (_native_threads_only) {
        _PR_MD_LOCK(&lock->ilock);
        PR_ASSERT(lock->owner == 0);
        lock->owner = me;
        return;
    }

    if (!_PR_IS_NATIVE_THREAD(me)) {
        _PR_INTSOFF(is);
    }

    PR_ASSERT(_PR_IS_NATIVE_THREAD(me) || _PR_MD_GET_INTSOFF() != 0);

retry:
    _PR_LOCK_LOCK(lock);
    if (lock->owner == 0) {
        /* Just got the lock */
        lock->owner = me;
        lock->priority = me->priority;
        /* Add the granted lock to this owning thread's lock list */
        PR_APPEND_LINK(&lock->links, &me->lockList);
        _PR_LOCK_UNLOCK(lock);
        if (!_PR_IS_NATIVE_THREAD(me)) {
            _PR_FAST_INTSON(is);
        }
        return;
    }

    /* If this thread already owns this lock, then it is a deadlock */
    PR_ASSERT(lock->owner != me);

    PR_ASSERT(_PR_IS_NATIVE_THREAD(me) || _PR_MD_GET_INTSOFF() != 0);

#if 0
    if (me->priority > lock->owner->priority) {
        /*
        ** Give the lock owner a priority boost until we get the
        ** lock. Record the priority we boosted it to.
        */
        lock->boostPriority = me->priority;
        _PR_SetThreadPriority(lock->owner, me->priority);
    }
#endif

    /*
    Add this thread to the asked for lock's list of waiting threads.  We
    add this thread thread in the right priority order so when the unlock
    occurs, the thread with the higher priority will get the lock.
    */
    q = lock->waitQ.next;
    if (q == &lock->waitQ || _PR_THREAD_CONDQ_PTR(q)->priority ==
        _PR_THREAD_CONDQ_PTR(lock->waitQ.prev)->priority) {
        /*
         * If all the threads in the lock waitQ have the same priority,
         * then avoid scanning the list:  insert the element at the end.
         */
        q = &lock->waitQ;
    } else {
        /* Sort thread into lock's waitQ at appropriate point */
        /* Now scan the list for where to insert this entry */
        while (q != &lock->waitQ) {
            t = _PR_THREAD_CONDQ_PTR(lock->waitQ.next);
            if (me->priority > t->priority) {
                /* Found a lower priority thread to insert in front of */
                break;
            }
            q = q->next;
        }
    }
    PR_INSERT_BEFORE(&me->waitQLinks, q);

    /*
    Now grab the threadLock since we are about to change the state.  We have
    to do this since a PR_Suspend or PR_SetThreadPriority type call that takes
    a PRThread* as an argument could be changing the state of this thread from
    a thread running on a different cpu.
    */

    _PR_THREAD_LOCK(me);
    me->state = _PR_LOCK_WAIT;
    me->wait.lock = lock;
    _PR_THREAD_UNLOCK(me);

    _PR_LOCK_UNLOCK(lock);

    _PR_MD_WAIT(me, PR_INTERVAL_NO_TIMEOUT);
    goto retry;

#endif  /* _PR_GLOBAL_THREADS_ONLY */
}

/*
** Unlock the lock.
*/
PR_IMPLEMENT(PRStatus) PR_Unlock(PRLock *lock)
{
    PRCList *q;
    PRThreadPriority pri, boost;
    PRIntn is;
    PRThread *me = _PR_MD_CURRENT_THREAD();

    PR_ASSERT(lock != NULL);
    PR_ASSERT(lock->owner == me);
    PR_ASSERT(me != suspendAllThread);
    PR_ASSERT(!(me->flags & _PR_IDLE_THREAD));
    if (lock->owner != me) {
        return PR_FAILURE;
    }

#ifdef _PR_GLOBAL_THREADS_ONLY
    lock->owner = 0;
    _PR_MD_UNLOCK(&lock->ilock);
    return PR_SUCCESS;
#else  /* _PR_GLOBAL_THREADS_ONLY */

    if (_native_threads_only) {
        lock->owner = 0;
        _PR_MD_UNLOCK(&lock->ilock);
        return PR_SUCCESS;
    }

    if (!_PR_IS_NATIVE_THREAD(me)) {
        _PR_INTSOFF(is);
    }
    _PR_LOCK_LOCK(lock);

    /* Remove the lock from the owning thread's lock list */
    PR_REMOVE_LINK(&lock->links);
    pri = lock->priority;
    boost = lock->boostPriority;
    if (boost > pri) {
        /*
        ** We received a priority boost during the time we held the lock.
        ** We need to figure out what priority to move to by scanning
        ** down our list of lock's that we are still holding and using
        ** the highest boosted priority found.
        */
        q = me->lockList.next;
        while (q != &me->lockList) {
            PRLock *ll = _PR_LOCK_PTR(q);
            if (ll->boostPriority > pri) {
                pri = ll->boostPriority;
            }
            q = q->next;
        }
        if (pri != me->priority) {
            _PR_SetThreadPriority(me, pri);
        }
    }

    /* Unblock the first waiting thread */
    q = lock->waitQ.next;
    if (q != &lock->waitQ) {
        _PR_UnblockLockWaiter(lock);
    }
    lock->boostPriority = PR_PRIORITY_LOW;
    lock->owner = 0;
    _PR_LOCK_UNLOCK(lock);
    if (!_PR_IS_NATIVE_THREAD(me)) {
        _PR_INTSON(is);
    }
    return PR_SUCCESS;
#endif  /* _PR_GLOBAL_THREADS_ONLY */
}

/*
**  If the current thread owns |lock|, this assertion is guaranteed to
**  succeed.  Otherwise, the behavior of this function is undefined.
*/
PR_IMPLEMENT(void) PR_AssertCurrentThreadOwnsLock(PRLock *lock)
{
    PRThread *me = _PR_MD_CURRENT_THREAD();
    PR_ASSERT(lock->owner == me);
}

/*
** Test and then lock the lock if it's not already locked by some other
** thread. Return PR_FALSE if some other thread owned the lock at the
** time of the call.
*/
PR_IMPLEMENT(PRBool) PR_TestAndLock(PRLock *lock)
{
    PRThread *me = _PR_MD_CURRENT_THREAD();
    PRBool rv = PR_FALSE;
    PRIntn is;

#ifdef _PR_GLOBAL_THREADS_ONLY
    is = _PR_MD_TEST_AND_LOCK(&lock->ilock);
    if (is == 0) {
        lock->owner = me;
        return PR_TRUE;
    }
    return PR_FALSE;
#else  /* _PR_GLOBAL_THREADS_ONLY */

#ifndef _PR_LOCAL_THREADS_ONLY
    if (_native_threads_only) {
        is = _PR_MD_TEST_AND_LOCK(&lock->ilock);
        if (is == 0) {
            lock->owner = me;
            return PR_TRUE;
        }
        return PR_FALSE;
    }
#endif

    if (!_PR_IS_NATIVE_THREAD(me)) {
        _PR_INTSOFF(is);
    }

    _PR_LOCK_LOCK(lock);
    if (lock->owner == 0) {
        /* Just got the lock */
        lock->owner = me;
        lock->priority = me->priority;
        /* Add the granted lock to this owning thread's lock list */
        PR_APPEND_LINK(&lock->links, &me->lockList);
        rv = PR_TRUE;
    }
    _PR_LOCK_UNLOCK(lock);

    if (!_PR_IS_NATIVE_THREAD(me)) {
        _PR_INTSON(is);
    }
    return rv;
#endif  /* _PR_GLOBAL_THREADS_ONLY */
}

/************************************************************************/
/************************************************************************/
/***********************ROUTINES FOR DCE EMULATION***********************/
/************************************************************************/
/************************************************************************/
PR_IMPLEMENT(PRStatus) PRP_TryLock(PRLock *lock)
{
    return (PR_TestAndLock(lock)) ? PR_SUCCESS : PR_FAILURE;
}