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

/*
 * 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 kernel_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)
{
        *cv = CONDVAR_INITIALIZER(*cv);
}

/** 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_signal(&cv->wq);
}

/** 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_wake_all(&cv->wq);
}

/** Wait for the condition becoming true.
 *
 * @param cv            Condition variable.
 * @param mtx           Mutex.
 * @param usec          Timeout value in microseconds.
 *
 * @return              See comment for waitq_sleep_timeout().
 */
errno_t __condvar_wait_timeout_mutex(condvar_t *cv, mutex_t *mtx, uint32_t usec)
{
        wait_guard_t guard = waitq_sleep_prepare(&cv->wq);

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

        errno_t rc = waitq_sleep_timeout_unsafe(&cv->wq, usec, SYNCH_FLAGS_NON_BLOCKING, guard);

        mutex_lock(mtx);
        return rc;
}

errno_t __condvar_wait_mutex(condvar_t *cv, mutex_t *mtx)
{
        wait_guard_t guard = waitq_sleep_prepare(&cv->wq);

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

        errno_t rc = waitq_sleep_unsafe(&cv->wq, guard);

        mutex_lock(mtx);
        return rc;
}

/** Same as __condvar_wait_timeout_mutex(), except for spinlock_t. */
errno_t __condvar_wait_timeout_spinlock(condvar_t *cv, spinlock_t *lock,
    uint32_t usec)
{
        wait_guard_t guard = waitq_sleep_prepare(&cv->wq);

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

        errno_t rc = waitq_sleep_timeout_unsafe(&cv->wq, usec,
            SYNCH_FLAGS_NON_BLOCKING, guard);

        spinlock_lock(lock);
        return rc;
}

errno_t __condvar_wait_spinlock(condvar_t *cv, spinlock_t *mtx)
{
        wait_guard_t guard = waitq_sleep_prepare(&cv->wq);

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

        errno_t rc = waitq_sleep_unsafe(&cv->wq, guard);

        spinlock_lock(mtx);
        return rc;
}

/** Same as __condvar_wait_timeout_mutex(), except for irq_spinlock_t. */
errno_t __condvar_wait_timeout_irq_spinlock(condvar_t *cv,
    irq_spinlock_t *irq_lock, uint32_t usec)
{
        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);

        irq_lock->guard = guard;
        irq_lock->ipl = ipl;

        return rc;
}

/** Same as __condvar_wait_mutex(), except for irq_spinlock_t. */
errno_t __condvar_wait_irq_spinlock(condvar_t *cv, irq_spinlock_t *irq_lock)
{
        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;

        rc = __condvar_wait_spinlock(cv, &irq_lock->lock);

        irq_lock->guard = guard;
        irq_lock->ipl = ipl;

        return rc;
}

/** @}
 */