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/*

 * 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.

 */

#include <synch/waitq.h>

#include <synch/synch.h>

#include <synch/spinlock.h>

#include <proc/thread.h>

#include <arch/asm.h>

#include <arch/types.h>

#include <time/timeout.h>

#include <arch.h>

#include <context.h>

#include <list.h>

/** Initialize wait queue

 *

 * Initialize wait queue.

 *

 * @param wq Pointer to wait queue to be initialized.

 */

void waitq_initialize(waitq_t *wq)

{

    spinlock_initialize(&wq->lock);

    list_initialize(&wq->head);

    wq->missed_wakeups = 0;

}

/** Handle timeout during waitq_sleep_timeout() call

 *

 * This routine is called when waitq_sleep_timeout() timeouts.

 * Interrupts are disabled.

 *

 * It is supposed to try to remove 'its' thread from the wait queue;

 * it can eventually fail to achieve this goal when these two events

 * overlap. In that case it behaves just as though there was no

 * timeout at all.

 *

 * @param data Pointer to the thread that called waitq_sleep_timeout().

 */

void waitq_interrupted_sleep(void *data)

{

    thread_t *t = (thread_t *) data;

    waitq_t *wq;

    int do_wakeup = 0;

    spinlock_lock(&threads_lock);

    if (!list_member(&t->threads_link, &threads_head))

        goto out;

grab_locks:

    spinlock_lock(&t->lock);

    if (wq = t->sleep_queue) {

        if (!spinlock_trylock(&wq->lock)) {

            spinlock_unlock(&t->lock);

            goto grab_locks; /* avoid deadlock */

        }

        list_remove(&t->wq_link);

        t->saved_context = t->sleep_timeout_context;

        do_wakeup = 1;

        spinlock_unlock(&wq->lock);

        t->sleep_queue = NULL;

    }

    t->timeout_pending = 0;

    spinlock_unlock(&t->lock);

    if (do_wakeup) thread_ready(t);

out:

    spinlock_unlock(&threads_lock);

}

/** Sleep until either wakeup or timeout occurs

 *

 * This is a sleep implementation which allows itself to be

 * interrupted from the sleep, restoring a failover context.

 *

 * Sleepers are organised in FIFO fashion in a structure called wait queue.

 *

 * This function is really basic in that other functions as waitq_sleep()

 * and all the *_timeout() functions use it.

 *

 * @param wq Pointer to wait queue.

 * @param usec Timeout value in microseconds.

 * @param nonblocking Controls whether only a conditional sleep

 *        (non-blocking sleep) is called for when the usec argument is 0.

 *

 * Relation between 'usec' and 'nonblocking' is described by this table:

 *

 * usec | nonblocking | what happens if there is no missed_wakeup

 * -----+-------------+--------------------------------------------

 *  0   | 0       | blocks without timeout until wakeup

 *  0   | <> 0        | immediately returns ESYNCH_WOULD_BLOCK

 *  > 0 | x       | blocks with timeout until timeout or wakeup

 *

 * @return Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT,

 *         ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.

 *

 * Meaning of the return values is described by the following chart:

 *

 * ESYNCH_WOULD_BLOCK   Sleep failed because at the time of the call,

 *          there was no pending wakeup.

 * ESYNCH_TIMEOUT   Sleep timed out.

 * ESYNCH_OK_ATOMIC     Sleep succeeded; at the time of the call,

 *          where was a pending wakeup.

 * ESYNCH_OK_BLOCKED    Sleep succeeded; the full sleep was attempted.

 */

int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int nonblocking)

{

    volatile pri_t pri; /* must be live after context_restore() */

restart:

    pri = cpu_priority_high();

    /*

     * Busy waiting for a delayed timeout.

     * This is an important fix for the race condition between

     * a delayed timeout and a next call to waitq_sleep_timeout().

     * Simply, the thread is not allowed to go to sleep if

     * there are timeouts in progress.

     */

    spinlock_lock(&THREAD->lock);

    if (THREAD->timeout_pending) {

        spinlock_unlock(&THREAD->lock);

        cpu_priority_restore(pri);     

        goto restart;

    }

    spinlock_unlock(&THREAD->lock);

    spinlock_lock(&wq->lock);

    /* checks whether to go to sleep at all */

    if (wq->missed_wakeups) {

        wq->missed_wakeups--;

        spinlock_unlock(&wq->lock);

        cpu_priority_restore(pri);

        return ESYNCH_OK_ATOMIC;

    }

    else {

        if (nonblocking && (usec == 0)) {

            /* return immediatelly instead of going to sleep */

            spinlock_unlock(&wq->lock);

            cpu_priority_restore(pri);

            return ESYNCH_WOULD_BLOCK;

        }

    }

    /*

     * Now we are firmly decided to go to sleep.

     */

    spinlock_lock(&THREAD->lock);

    if (usec) {

        /* We use the timeout variant. */

        if (!context_save(&THREAD->sleep_timeout_context)) {

            /*

             * Short emulation of scheduler() return code.

             */

            before_thread_runs();

            spinlock_unlock(&THREAD->lock);

            cpu_priority_restore(pri);

            return ESYNCH_TIMEOUT;

        }

        THREAD->timeout_pending = 1;

        timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_interrupted_sleep, THREAD);

    }

    list_append(&THREAD->wq_link, &wq->head);

    /*

     * Suspend execution.

     */

    THREAD->state = Sleeping;

    THREAD->sleep_queue = wq;

    spinlock_unlock(&THREAD->lock);

    scheduler();    /* wq->lock is released in scheduler_separated_stack() */

    cpu_priority_restore(pri);

    return ESYNCH_OK_BLOCKED;

}

/** Wake up first thread sleeping in a wait queue

 *

 * Wake up first thread sleeping in a wait queue.

 * This is the SMP- and IRQ-safe wrapper meant for

 * general use.

 *

 * Besides its 'normal' wakeup operation, it attempts

 * to unregister possible timeout.

 *

 * @param wq Pointer to wait queue.

 * @param all If this is non-zero, all sleeping threads

 *        will be woken up and missed count will be zeroed.

 */

void waitq_wakeup(waitq_t *wq, int all)

{

    pri_t pri;

    pri = cpu_priority_high();

    spinlock_lock(&wq->lock);

    _waitq_wakeup_unsafe(wq, all);

    spinlock_unlock(&wq->lock);

    cpu_priority_restore(pri); 

}

/** Internal SMP- and IRQ-unsafe version of waitq_wakeup()

 *

 * This is the internal SMP- and IRQ-unsafe version

 * of waitq_wakeup(). It assumes wq->lock is already

 * locked and interrupts are already disabled.

 *

 * @param wq Pointer to wait queue.

 * @param all If this is non-zero, all sleeping threads

 *        will be woken up and missed count will be zeroed.

 */

void _waitq_wakeup_unsafe(waitq_t *wq, int all)

{

    thread_t *t;

loop:  

    if (list_empty(&wq->head)) {

        wq->missed_wakeups++;

        if (all) wq->missed_wakeups = 0;

        return;

    }

    t = list_get_instance(wq->head.next, thread_t, wq_link);

    list_remove(&t->wq_link);

    spinlock_lock(&t->lock);

    if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))

        t->timeout_pending = 0;

    t->sleep_queue = NULL;

    spinlock_unlock(&t->lock);

    thread_ready(t);

    if (all) goto loop;

}