source: mainline/kernel/generic/src/synch/condvar.c@ 46577995

/*
 * Copyright (c) 2001-2004 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup sync
 * @{
 */

/**
 * @file
 * @brief       Condition variables.
 */

#include <synch/condvar.h>
#include <synch/mutex.h>
#include <synch/spinlock.h>
#include <synch/waitq.h>
#include <arch.h>

/** Initialize condition variable.
 *
 * @param cv            Condition variable.
 */
void condvar_initialize(condvar_t *cv)
{
        waitq_initialize(&cv->wq);
}

/** Signal the condition has become true to the first waiting thread by waking
 * it up.
 *
 * @param cv            Condition variable.
 */
void condvar_signal(condvar_t *cv)
{
        waitq_wakeup(&cv->wq, WAKEUP_FIRST);
}

/** Signal the condition has become true to all waiting threads by waking
 * them up.
 *
 * @param cv            Condition variable.
 */
void condvar_broadcast(condvar_t *cv)
{
        waitq_wakeup(&cv->wq, WAKEUP_ALL);
}

/** Wait for the condition becoming true.
 *
 * @param cv            Condition variable.
 * @param mtx           Mutex.
 * @param usec          Timeout value in microseconds.
 * @param flags         Select mode of operation.
 *
 * For exact description of meaning of possible combinations of usec and flags,
 * see comment for waitq_sleep_timeout().  Note that when
 * SYNCH_FLAGS_NON_BLOCKING is specified here, EAGAIN is always
 * returned.
 *
 * @return              See comment for waitq_sleep_timeout().
 */
errno_t _condvar_wait_timeout(condvar_t *cv, mutex_t *mtx, uint32_t usec, int flags)
{
        errno_t rc;
        ipl_t ipl;
        bool blocked;

        ipl = waitq_sleep_prepare(&cv->wq);
        /* Unlock only after the waitq is locked so we don't miss a wakeup. */
        mutex_unlock(mtx);

        cv->wq.missed_wakeups = 0;      /* Enforce blocking. */
        rc = waitq_sleep_timeout_unsafe(&cv->wq, usec, flags, &blocked);
        assert(blocked || rc != EOK);

        waitq_sleep_finish(&cv->wq, blocked, ipl);
        /* Lock only after releasing the waitq to avoid a possible deadlock. */
        mutex_lock(mtx);

        return rc;
}

/** Wait for the condition to become true with a locked spinlock.
 * 
 * The function is not aware of irq_spinlock. Therefore do not even
 * try passing irq_spinlock_t to it. Use _condvar_wait_timeout_irq_spinlock()
 * instead.
 *
 * @param cv            Condition variable.
 * @param lock          Locked spinlock.
 * @param usec          Timeout value in microseconds.
 * @param flags         Select mode of operation.
 *
 * For exact description of meaning of possible combinations of usec and flags,
 * see comment for waitq_sleep_timeout().  Note that when
 * SYNCH_FLAGS_NON_BLOCKING is specified here, EAGAIN is always
 * returned.
 *
 * @return See comment for waitq_sleep_timeout().
 */
errno_t _condvar_wait_timeout_spinlock_impl(condvar_t *cv, spinlock_t *lock, 
        uint32_t usec, int flags)
{
        errno_t rc;
        ipl_t ipl;
        bool blocked;

        ipl = waitq_sleep_prepare(&cv->wq);

        /* Unlock only after the waitq is locked so we don't miss a wakeup. */
        spinlock_unlock(lock);

        cv->wq.missed_wakeups = 0;      /* Enforce blocking. */
        rc = waitq_sleep_timeout_unsafe(&cv->wq, usec, flags, &blocked);
        assert(blocked || rc != EOK);

        waitq_sleep_finish(&cv->wq, blocked, ipl);
        /* Lock only after releasing the waitq to avoid a possible deadlock. */
        spinlock_lock(lock);
        
        return rc;
}

/** Wait for the condition to become true with a locked irq spinlock.
 * 
 * @param cv            Condition variable.
 * @param lock          Locked irq spinlock.
 * @param usec          Timeout value in microseconds.
 * @param flags         Select mode of operation.
 *
 * For exact description of meaning of possible combinations of usec and flags,
 * see comment for waitq_sleep_timeout().  Note that when
 * SYNCH_FLAGS_NON_BLOCKING is specified here, EAGAIN is always
 * returned.
 *
 * @return See comment for waitq_sleep_timeout().
 */
errno_t _condvar_wait_timeout_irq_spinlock(condvar_t *cv, irq_spinlock_t *irq_lock, 
        uint32_t usec, int flags)
{
        errno_t rc;
        /* Save spinlock's state so we can restore it correctly later on. */
        ipl_t ipl = irq_lock->ipl;
        bool guard = irq_lock->guard;
        
        irq_lock->guard = false;
        
        /* 
         * waitq_prepare() restores interrupts to the current state, 
         * ie disabled. Therefore, interrupts will remain disabled while 
         * it spins waiting for a pending timeout handler to complete. 
         * Although it spins with interrupts disabled there can only
         * be a pending timeout if we failed to cancel an imminent
         * timeout (on another cpu) during a wakeup. As a result the 
         * timeout handler is guaranteed to run (it is most likely already 
         * running) and there is no danger of a deadlock.
         */
        rc = _condvar_wait_timeout_spinlock(cv, &irq_lock->lock, usec, flags);
        
        irq_lock->guard = guard;
        irq_lock->ipl = ipl;
        
        return rc;
}


/** @}
 */