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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.

 */

/**

 * @file    waitq.c

 * @brief   Wait queue.

 *

 * Wait queue is the basic synchronization primitive upon which all

 * other synchronization primitives build.

 *

 * It allows threads to wait for an event in first-come, first-served

 * fashion. Conditional operation as well as timeouts and interruptions

 * are supported.

 */

#include <synch/waitq.h>

#include <synch/synch.h>

#include <synch/spinlock.h>

#include <proc/thread.h>

#include <proc/scheduler.h>

#include <arch/asm.h>

#include <arch/types.h>

#include <typedefs.h>

#include <time/timeout.h>

#include <arch.h>

#include <context.h>

#include <adt/list.h>

static void waitq_timeouted_sleep(void *data);

/** 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, "waitq_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_timeouted_sleep(void *data)

{

    thread_t *t = (thread_t *) data;

    waitq_t *wq;

    bool do_wakeup = false;

    spinlock_lock(&threads_lock);

    if (!thread_exists(t))

        goto out;

grab_locks:

    spinlock_lock(&t->lock);

    if ((wq = t->sleep_queue)) {        /* assignment */

        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 = true;

        t->sleep_queue = NULL;

        spinlock_unlock(&wq->lock);

    }

    t->timeout_pending = false;

    spinlock_unlock(&t->lock);

    if (do_wakeup)

        thread_ready(t);

out:

    spinlock_unlock(&threads_lock);

}

/** Interrupt sleeping thread.

 *

 * This routine attempts to interrupt a thread from its sleep in a waitqueue.

 * If the thread is not found sleeping, no action is taken.

 *

 * @param t Thread to be interrupted.

 */

void waitq_interrupt_sleep(thread_t *t)

{

    waitq_t *wq;

    bool do_wakeup = false;

    ipl_t ipl;

    ipl = interrupts_disable();

    spinlock_lock(&threads_lock);

    if (!thread_exists(t))

        goto out;

grab_locks:

    spinlock_lock(&t->lock);

    if ((wq = t->sleep_queue)) {        /* assignment */

        if (!(t->sleep_interruptible)) {

            /*

             * The sleep cannot be interrupted.

             */

            spinlock_unlock(&t->lock);

            goto out;

        }

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

            spinlock_unlock(&t->lock);

            goto grab_locks;    /* avoid deadlock */

        }

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

            t->timeout_pending = false;

        list_remove(&t->wq_link);

        t->saved_context = t->sleep_interruption_context;

        do_wakeup = true;

        t->sleep_queue = NULL;

        spinlock_unlock(&wq->lock);

    }

    spinlock_unlock(&t->lock);

    if (do_wakeup)

        thread_ready(t);

out:

    spinlock_unlock(&threads_lock);

    interrupts_restore(ipl);

}

/** Sleep until either wakeup, timeout or interruption occurs

 *

 * This is a sleep implementation which allows itself to time out or to be

 * interrupted from the sleep, restoring a failover context.

 *

 * Sleepers are organised in a 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 in microseconds.

 * @param flags Specify mode of the sleep.

 *

 * The sleep can be interrupted only if the

 * SYNCH_FLAGS_INTERRUPTIBLE bit is specified in flags.

 * If usec is greater than zero, regardless of the value of the

 * SYNCH_FLAGS_NON_BLOCKING bit in flags, the call will not return until either timeout,

 * interruption or wakeup comes.

 *

 * If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is not set in flags, the call

 * will not return until wakeup or interruption comes.

 *

 * If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is set in flags, the call will

 * immediately return, reporting either success or failure.

 *

 * @return  Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT, ESYNCH_INTERRUPTED,

 *          ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.

 *

 * @li ESYNCH_WOULD_BLOCK means that the sleep failed because at the time

 * of the call there was no pending wakeup.

 *

 * @li ESYNCH_TIMEOUT means that the sleep timed out.

 *

 * @li ESYNCH_INTERRUPTED means that somebody interrupted the sleeping thread.

 *

 * @li ESYNCH_OK_ATOMIC means that the sleep succeeded and that there was

 * a pending wakeup at the time of the call. The caller was not put

 * asleep at all.

 *

 * @li ESYNCH_OK_BLOCKED means that the sleep succeeded; the full sleep was

 * attempted.

 */

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

{

    ipl_t ipl;

    int rc;

    ipl = waitq_sleep_prepare(wq);

    rc = waitq_sleep_timeout_unsafe(wq, usec, flags);

    waitq_sleep_finish(wq, rc, ipl);

    return rc;

}

/** Prepare to sleep in a waitq.

 *

 * This function will return holding the lock of the wait queue

 * and interrupts disabled.

 *

 * @param wq Wait queue.

 *

 * @return Interrupt level as it existed on entry to this function.

 */

ipl_t waitq_sleep_prepare(waitq_t *wq)

{

    ipl_t ipl;

restart:

    ipl = interrupts_disable();

    if (THREAD) {   /* needed during system initiailzation */

        /*

         * 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);

            interrupts_restore(ipl);

            goto restart;

        }

        spinlock_unlock(&THREAD->lock);

    }

    spinlock_lock(&wq->lock);

    return ipl;

}

/** Finish waiting in a wait queue.

 *

 * This function restores interrupts to the state that existed prior

 * to the call to waitq_sleep_prepare(). If necessary, the wait queue

 * lock is released.

 *

 * @param wq Wait queue.

 * @param rc Return code of waitq_sleep_timeout_unsafe().

 * @param ipl Interrupt level returned by waitq_sleep_prepare().

 */

void waitq_sleep_finish(waitq_t *wq, int rc, ipl_t ipl)

{

    switch (rc) {

    case ESYNCH_WOULD_BLOCK:

    case ESYNCH_OK_ATOMIC:

        spinlock_unlock(&wq->lock);

        break;

    default:

        break;

    }

    interrupts_restore(ipl);

}

/** Internal implementation of waitq_sleep_timeout().

 *

 * This function implements logic of sleeping in a wait queue.

 * This call must be preceeded by a call to waitq_sleep_prepare()

 * and followed by a call to waitq_slee_finish().

 *

 * @param wq See waitq_sleep_timeout().

 * @param usec See waitq_sleep_timeout().

 * @param flags See waitq_sleep_timeout().

 *

 * @return See waitq_sleep_timeout().

 */

int waitq_sleep_timeout_unsafe(waitq_t *wq, __u32 usec, int flags)

{

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

    if (wq->missed_wakeups) {

        wq->missed_wakeups--;

        return ESYNCH_OK_ATOMIC;

    }

    else {

        if ((flags & SYNCH_FLAGS_NON_BLOCKING) && (usec == 0)) {

            /* return immediatelly instead of going to sleep */

            return ESYNCH_WOULD_BLOCK;

        }

    }

    /*

     * Now we are firmly decided to go to sleep.

     */

    spinlock_lock(&THREAD->lock);

    if (flags & SYNCH_FLAGS_INTERRUPTIBLE) {

        /*

         * If the thread was already interrupted,

         * don't go to sleep at all.

         */

        if (THREAD->interrupted) {

            spinlock_unlock(&THREAD->lock);

            spinlock_unlock(&wq->lock);

            return ESYNCH_INTERRUPTED;

        }

        /*

         * Set context that will be restored if the sleep

         * of this thread is ever interrupted.

         */

        THREAD->sleep_interruptible = true;

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

            /* Short emulation of scheduler() return code. */

            spinlock_unlock(&THREAD->lock);

            return ESYNCH_INTERRUPTED;

        }

    } else {

        THREAD->sleep_interruptible = false;

    }

    if (usec) {

        /* We use the timeout variant. */

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

            /* Short emulation of scheduler() return code. */

            spinlock_unlock(&THREAD->lock);

            return ESYNCH_TIMEOUT;

        }

        THREAD->timeout_pending = true;

        timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_timeouted_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() */

    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, bool all)

{

    ipl_t ipl;

    ipl = interrupts_disable();

    spinlock_lock(&wq->lock);

    _waitq_wakeup_unsafe(wq, all);

    spinlock_unlock(&wq->lock);

    interrupts_restore(ipl);   

}

/** 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, bool 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);

    /*

     * Lock the thread prior to removing it from the wq.

     * This is not necessary because of mutual exclusion

     * (the link belongs to the wait queue), but because

     * of synchronization with waitq_timeouted_sleep()

     * and waitq_interrupt_sleep().

     *

     * In order for these two functions to work, the following

     * invariant must hold:

     *

     * t->sleep_queue != NULL <=> t sleeps in a wait queue

     *

     * For an observer who locks the thread, the invariant

     * holds only when the lock is held prior to removing

     * it from the wait queue.

     */

    spinlock_lock(&t->lock);

    list_remove(&t->wq_link);

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

        t->timeout_pending = false;

    t->sleep_queue = NULL;

    spinlock_unlock(&t->lock);

    thread_ready(t);

    if (all)

        goto loop;

}