source: mainline/kernel/generic/src/synch/mutex.c@ aca4a04

/*
 * 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 Mutexes.
 */

#include <synch/mutex.h>
#include <synch/semaphore.h>
#include <debug.h>
#include <arch.h>
#include <stacktrace.h>

/** Initialize mutex.
 *
 * @param mtx  Mutex.
 * @param type Type of the mutex.
 */
void mutex_initialize(mutex_t *mtx, mutex_type_t type)
{
        mtx->type = type;
        semaphore_initialize(&mtx->sem, 1);
}

/** Find out whether the mutex is currently locked.
 *
 * @param mtx           Mutex.
 * @return              True if the mutex is locked, false otherwise.
 */
bool mutex_locked(mutex_t *mtx)
{
        return semaphore_count_get(&mtx->sem) <= 0;
}

#define MUTEX_DEADLOCK_THRESHOLD        100000000

/** Acquire mutex.
 *
 * Timeout mode and non-blocking mode can be requested.
 *
 * @param mtx   Mutex.
 * @param usec  Timeout in microseconds.
 * @param flags Specify mode of operation.
 *
 * For exact description of possible combinations of
 * usec and flags, see comment for waitq_sleep_timeout().
 *
 * @return See comment for waitq_sleep_timeout().
 *
 */
int _mutex_lock_timeout(mutex_t *mtx, uint32_t usec, unsigned int flags)
{
        int rc;

        if ((mtx->type == MUTEX_PASSIVE) && (THREAD)) {
                rc = _semaphore_down_timeout(&mtx->sem, usec, flags);
        } else {
                ASSERT((mtx->type == MUTEX_ACTIVE) || (!THREAD));
                ASSERT(usec == SYNCH_NO_TIMEOUT);
                ASSERT(!(flags & SYNCH_FLAGS_INTERRUPTIBLE));
                
                unsigned int cnt = 0;
                bool deadlock_reported = false;
                do {
                        if (cnt++ > MUTEX_DEADLOCK_THRESHOLD) {
                                printf("cpu%u: looping on active mutex %p\n",
                                    CPU->id, mtx);
                                stack_trace();
                                cnt = 0;
                                deadlock_reported = true;
                        }
                        rc = semaphore_trydown(&mtx->sem);
                } while (SYNCH_FAILED(rc) &&
                    !(flags & SYNCH_FLAGS_NON_BLOCKING));
                if (deadlock_reported)
                        printf("cpu%u: not deadlocked\n", CPU->id);
        }

        return rc;
}

/** Release mutex.
 *
 * @param mtx Mutex.
 */
void mutex_unlock(mutex_t *mtx)
{
        semaphore_up(&mtx->sem);
}

/** @}
 */