source: mainline/uspace/lib/c/generic/fibril_synch.c@ 6e569bf

/*
 * Copyright (c) 2009 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 libc
 * @{
 */
/** @file
 */

#include <fibril_synch.h>
#include <fibril.h>
#include <async.h>
#include <adt/list.h>
#include <futex.h>
#include <sys/time.h>
#include <errno.h>
#include <assert.h>
#include <stacktrace.h>
#include <stdlib.h>
#include <stdio.h>
#include "private/async.h"
#include "private/fibril.h"

static void optimize_execution_power(void)
{
        /*
         * When waking up a worker fibril previously blocked in fibril
         * synchronization, chances are that there is an idle manager fibril
         * waiting for IPC, that could start executing the awakened worker
         * fibril right away. We try to detect this and bring the manager
         * fibril back to fruitful work.
         */
        async_poke();
}

static void print_deadlock(fibril_owner_info_t *oi)
{
        fibril_t *f = (fibril_t *) fibril_get_id();

        printf("Deadlock detected.\n");
        stacktrace_print();

        printf("Fibril %p waits for primitive %p.\n", f, oi);

        while (oi && oi->owned_by) {
                printf("Primitive %p is owned by fibril %p.\n",
                    oi, oi->owned_by);
                if (oi->owned_by == f)
                        break;
                stacktrace_print_fp_pc(
                    context_get_fp(&oi->owned_by->ctx),
                    context_get_pc(&oi->owned_by->ctx));
                printf("Fibril %p waits for primitive %p.\n",
                    oi->owned_by, oi->owned_by->waits_for);
                oi = oi->owned_by->waits_for;
        }
}


static void check_for_deadlock(fibril_owner_info_t *oi)
{
        while (oi && oi->owned_by) {
                if (oi->owned_by == (fibril_t *) fibril_get_id()) {
                        print_deadlock(oi);
                        abort();
                }
                oi = oi->owned_by->waits_for;
        }
}


void fibril_mutex_initialize(fibril_mutex_t *fm)
{
        fm->oi.owned_by = NULL;
        fm->counter = 1;
        list_initialize(&fm->waiters);
}

void fibril_mutex_lock(fibril_mutex_t *fm)
{
        fibril_t *f = (fibril_t *) fibril_get_id();

        futex_lock(&async_futex);
        if (fm->counter-- <= 0) {
                awaiter_t wdata;

                awaiter_initialize(&wdata);
                wdata.fid = fibril_get_id();
                wdata.wu_event.inlist = true;
                list_append(&wdata.wu_event.link, &fm->waiters);
                check_for_deadlock(&fm->oi);
                f->waits_for = &fm->oi;
                fibril_switch(FIBRIL_FROM_BLOCKED);
        } else {
                fm->oi.owned_by = f;
        }
        futex_unlock(&async_futex);
}

bool fibril_mutex_trylock(fibril_mutex_t *fm)
{
        bool locked = false;

        futex_lock(&async_futex);
        if (fm->counter > 0) {
                fm->counter--;
                fm->oi.owned_by = (fibril_t *) fibril_get_id();
                locked = true;
        }
        futex_unlock(&async_futex);

        return locked;
}

static void _fibril_mutex_unlock_unsafe(fibril_mutex_t *fm)
{
        if (fm->counter++ < 0) {
                link_t *tmp;
                awaiter_t *wdp;
                fibril_t *f;

                tmp = list_first(&fm->waiters);
                assert(tmp != NULL);
                wdp = list_get_instance(tmp, awaiter_t, wu_event.link);
                wdp->active = true;
                wdp->wu_event.inlist = false;

                f = (fibril_t *) wdp->fid;
                fm->oi.owned_by = f;
                f->waits_for = NULL;

                list_remove(&wdp->wu_event.link);
                fibril_add_ready(wdp->fid);
                optimize_execution_power();
        } else {
                fm->oi.owned_by = NULL;
        }
}

void fibril_mutex_unlock(fibril_mutex_t *fm)
{
        assert(fibril_mutex_is_locked(fm));
        futex_lock(&async_futex);
        _fibril_mutex_unlock_unsafe(fm);
        futex_unlock(&async_futex);
}

bool fibril_mutex_is_locked(fibril_mutex_t *fm)
{
        bool locked = false;

        futex_lock(&async_futex);
        if (fm->counter <= 0)
                locked = true;
        futex_unlock(&async_futex);

        return locked;
}

void fibril_rwlock_initialize(fibril_rwlock_t *frw)
{
        frw->oi.owned_by = NULL;
        frw->writers = 0;
        frw->readers = 0;
        list_initialize(&frw->waiters);
}

void fibril_rwlock_read_lock(fibril_rwlock_t *frw)
{
        fibril_t *f = (fibril_t *) fibril_get_id();

        futex_lock(&async_futex);
        if (frw->writers) {
                awaiter_t wdata;

                awaiter_initialize(&wdata);
                wdata.fid = (fid_t) f;
                wdata.wu_event.inlist = true;
                f->is_writer = false;
                list_append(&wdata.wu_event.link, &frw->waiters);
                check_for_deadlock(&frw->oi);
                f->waits_for = &frw->oi;
                fibril_switch(FIBRIL_FROM_BLOCKED);
        } else {
                /* Consider the first reader the owner. */
                if (frw->readers++ == 0)
                        frw->oi.owned_by = f;
        }
        futex_unlock(&async_futex);
}

void fibril_rwlock_write_lock(fibril_rwlock_t *frw)
{
        fibril_t *f = (fibril_t *) fibril_get_id();

        futex_lock(&async_futex);
        if (frw->writers || frw->readers) {
                awaiter_t wdata;

                awaiter_initialize(&wdata);
                wdata.fid = (fid_t) f;
                wdata.wu_event.inlist = true;
                f->is_writer = true;
                list_append(&wdata.wu_event.link, &frw->waiters);
                check_for_deadlock(&frw->oi);
                f->waits_for = &frw->oi;
                fibril_switch(FIBRIL_FROM_BLOCKED);
        } else {
                frw->oi.owned_by = f;
                frw->writers++;
        }
        futex_unlock(&async_futex);
}

static void _fibril_rwlock_common_unlock(fibril_rwlock_t *frw)
{
        futex_lock(&async_futex);
        if (frw->readers) {
                if (--frw->readers) {
                        if (frw->oi.owned_by == (fibril_t *) fibril_get_id()) {
                                /*
                                 * If this reader firbril was considered the
                                 * owner of this rwlock, clear the ownership
                                 * information even if there are still more
                                 * readers.
                                 *
                                 * This is the limitation of the detection
                                 * mechanism rooted in the fact that tracking
                                 * all readers would require dynamically
                                 * allocated memory for keeping linkage info.
                                 */
                                frw->oi.owned_by = NULL;
                        }
                        goto out;
                }
        } else {
                frw->writers--;
        }

        assert(!frw->readers && !frw->writers);

        frw->oi.owned_by = NULL;

        while (!list_empty(&frw->waiters)) {
                link_t *tmp = list_first(&frw->waiters);
                awaiter_t *wdp;
                fibril_t *f;

                wdp = list_get_instance(tmp, awaiter_t, wu_event.link);
                f = (fibril_t *) wdp->fid;

                f->waits_for = NULL;

                if (f->is_writer) {
                        if (frw->readers)
                                break;
                        wdp->active = true;
                        wdp->wu_event.inlist = false;
                        list_remove(&wdp->wu_event.link);
                        fibril_add_ready(wdp->fid);
                        frw->writers++;
                        frw->oi.owned_by = f;
                        optimize_execution_power();
                        break;
                } else {
                        wdp->active = true;
                        wdp->wu_event.inlist = false;
                        list_remove(&wdp->wu_event.link);
                        fibril_add_ready(wdp->fid);
                        if (frw->readers++ == 0) {
                                /* Consider the first reader the owner. */
                                frw->oi.owned_by = f;
                        }
                        optimize_execution_power();
                }
        }
out:
        futex_unlock(&async_futex);
}

void fibril_rwlock_read_unlock(fibril_rwlock_t *frw)
{
        assert(fibril_rwlock_is_read_locked(frw));
        _fibril_rwlock_common_unlock(frw);
}

void fibril_rwlock_write_unlock(fibril_rwlock_t *frw)
{
        assert(fibril_rwlock_is_write_locked(frw));
        _fibril_rwlock_common_unlock(frw);
}

bool fibril_rwlock_is_read_locked(fibril_rwlock_t *frw)
{
        bool locked = false;

        futex_lock(&async_futex);
        if (frw->readers)
                locked = true;
        futex_unlock(&async_futex);

        return locked;
}

bool fibril_rwlock_is_write_locked(fibril_rwlock_t *frw)
{
        bool locked = false;

        futex_lock(&async_futex);
        if (frw->writers) {
                assert(frw->writers == 1);
                locked = true;
        }
        futex_unlock(&async_futex);

        return locked;
}

bool fibril_rwlock_is_locked(fibril_rwlock_t *frw)
{
        return fibril_rwlock_is_read_locked(frw) ||
            fibril_rwlock_is_write_locked(frw);
}

void fibril_condvar_initialize(fibril_condvar_t *fcv)
{
        list_initialize(&fcv->waiters);
}

errno_t
fibril_condvar_wait_timeout(fibril_condvar_t *fcv, fibril_mutex_t *fm,
    suseconds_t timeout)
{
        awaiter_t wdata;

        assert(fibril_mutex_is_locked(fm));

        if (timeout < 0)
                return ETIMEOUT;

        awaiter_initialize(&wdata);
        wdata.fid = fibril_get_id();
        wdata.to_event.inlist = timeout > 0;
        wdata.wu_event.inlist = true;

        futex_lock(&async_futex);
        if (timeout) {
                getuptime(&wdata.to_event.expires);
                tv_add_diff(&wdata.to_event.expires, timeout);
                async_insert_timeout(&wdata);
        }
        list_append(&wdata.wu_event.link, &fcv->waiters);
        _fibril_mutex_unlock_unsafe(fm);
        fibril_switch(FIBRIL_FROM_BLOCKED);
        futex_unlock(&async_futex);

        // XXX: This could be replaced with an unlocked version to get rid
        // of the unlock-lock pair. I deliberately don't do that because
        // further changes would most likely need to revert that optimization.
        fibril_mutex_lock(fm);

        futex_lock(&async_futex);
        if (wdata.to_event.inlist)
                list_remove(&wdata.to_event.link);
        if (wdata.wu_event.inlist)
                list_remove(&wdata.wu_event.link);
        futex_unlock(&async_futex);

        return wdata.to_event.occurred ? ETIMEOUT : EOK;
}

void fibril_condvar_wait(fibril_condvar_t *fcv, fibril_mutex_t *fm)
{
        errno_t rc;

        rc = fibril_condvar_wait_timeout(fcv, fm, 0);
        assert(rc == EOK);
}

static void _fibril_condvar_wakeup_common(fibril_condvar_t *fcv, bool once)
{
        link_t *tmp;
        awaiter_t *wdp;

        futex_lock(&async_futex);
        while (!list_empty(&fcv->waiters)) {
                tmp = list_first(&fcv->waiters);
                wdp = list_get_instance(tmp, awaiter_t, wu_event.link);
                list_remove(&wdp->wu_event.link);
                wdp->wu_event.inlist = false;
                if (!wdp->active) {
                        wdp->active = true;
                        fibril_add_ready(wdp->fid);
                        optimize_execution_power();
                        if (once)
                                break;
                }
        }
        futex_unlock(&async_futex);
}

void fibril_condvar_signal(fibril_condvar_t *fcv)
{
        _fibril_condvar_wakeup_common(fcv, true);
}

void fibril_condvar_broadcast(fibril_condvar_t *fcv)
{
        _fibril_condvar_wakeup_common(fcv, false);
}

/** Timer fibril.
 *
 * @param arg   Timer
 */
static errno_t fibril_timer_func(void *arg)
{
        fibril_timer_t *timer = (fibril_timer_t *) arg;
        errno_t rc;

        fibril_mutex_lock(timer->lockp);

        while (timer->state != fts_cleanup) {
                switch (timer->state) {
                case fts_not_set:
                case fts_fired:
                        fibril_condvar_wait(&timer->cv, timer->lockp);
                        break;
                case fts_active:
                        rc = fibril_condvar_wait_timeout(&timer->cv,
                            timer->lockp, timer->delay);
                        if (rc == ETIMEOUT && timer->state == fts_active) {
                                timer->state = fts_fired;
                                timer->handler_fid = fibril_get_id();
                                fibril_mutex_unlock(timer->lockp);
                                timer->fun(timer->arg);
                                fibril_mutex_lock(timer->lockp);
                                timer->handler_fid = 0;
                        }
                        break;
                case fts_cleanup:
                case fts_clean:
                        assert(false);
                        break;
                }
        }

        /* Acknowledge timer fibril has finished cleanup. */
        timer->state = fts_clean;
        fibril_condvar_broadcast(&timer->cv);
        fibril_mutex_unlock(timer->lockp);

        return 0;
}

/** Create new timer.
 *
 * @return              New timer on success, @c NULL if out of memory.
 */
fibril_timer_t *fibril_timer_create(fibril_mutex_t *lock)
{
        fid_t fid;
        fibril_timer_t *timer;

        timer = calloc(1, sizeof(fibril_timer_t));
        if (timer == NULL)
                return NULL;

        fid = fibril_create(fibril_timer_func, (void *) timer);
        if (fid == 0) {
                free(timer);
                return NULL;
        }

        fibril_mutex_initialize(&timer->lock);
        fibril_condvar_initialize(&timer->cv);

        timer->fibril = fid;
        timer->state = fts_not_set;
        timer->lockp = (lock != NULL) ? lock : &timer->lock;

        fibril_add_ready(fid);
        return timer;
}

/** Destroy timer.
 *
 * @param timer         Timer, must not be active or accessed by other threads.
 */
void fibril_timer_destroy(fibril_timer_t *timer)
{
        fibril_mutex_lock(timer->lockp);
        assert(timer->state == fts_not_set || timer->state == fts_fired);

        /* Request timer fibril to terminate. */
        timer->state = fts_cleanup;
        fibril_condvar_broadcast(&timer->cv);

        /* Wait for timer fibril to terminate */
        while (timer->state != fts_clean)
                fibril_condvar_wait(&timer->cv, timer->lockp);
        fibril_mutex_unlock(timer->lockp);

        free(timer);
}

/** Set timer.
 *
 * Set timer to execute a callback function after the specified
 * interval.
 *
 * @param timer         Timer
 * @param delay         Delay in microseconds
 * @param fun           Callback function
 * @param arg           Argument for @a fun
 */
void fibril_timer_set(fibril_timer_t *timer, suseconds_t delay,
    fibril_timer_fun_t fun, void *arg)
{
        fibril_mutex_lock(timer->lockp);
        fibril_timer_set_locked(timer, delay, fun, arg);
        fibril_mutex_unlock(timer->lockp);
}

/** Set locked timer.
 *
 * Set timer to execute a callback function after the specified
 * interval. Must be called when the timer is locked.
 *
 * @param timer         Timer
 * @param delay         Delay in microseconds
 * @param fun           Callback function
 * @param arg           Argument for @a fun
 */
void fibril_timer_set_locked(fibril_timer_t *timer, suseconds_t delay,
    fibril_timer_fun_t fun, void *arg)
{
        assert(fibril_mutex_is_locked(timer->lockp));
        assert(timer->state == fts_not_set || timer->state == fts_fired);
        timer->state = fts_active;
        timer->delay = delay;
        timer->fun = fun;
        timer->arg = arg;
        fibril_condvar_broadcast(&timer->cv);
}

/** Clear timer.
 *
 * Clears (cancels) timer and returns last state of the timer.
 * This can be one of:
 *    - fts_not_set     If the timer has not been set or has been cleared
 *    - fts_active      Timer was set but did not fire
 *    - fts_fired       Timer fired
 *
 * @param timer         Timer
 * @return              Last timer state
 */
fibril_timer_state_t fibril_timer_clear(fibril_timer_t *timer)
{
        fibril_timer_state_t old_state;

        fibril_mutex_lock(timer->lockp);
        old_state = fibril_timer_clear_locked(timer);
        fibril_mutex_unlock(timer->lockp);

        return old_state;
}

/** Clear locked timer.
 *
 * Clears (cancels) timer and returns last state of the timer.
 * This can be one of:
 *    - fts_not_set     If the timer has not been set or has been cleared
 *    - fts_active      Timer was set but did not fire
 *    - fts_fired       Timer fired
 * Must be called when the timer is locked.
 *
 * @param timer         Timer
 * @return              Last timer state
 */
fibril_timer_state_t fibril_timer_clear_locked(fibril_timer_t *timer)
{
        fibril_timer_state_t old_state;

        assert(fibril_mutex_is_locked(timer->lockp));

        while (timer->handler_fid != 0) {
                if (timer->handler_fid == fibril_get_id()) {
                        printf("Deadlock detected.\n");
                        stacktrace_print();
                        printf("Fibril %zx is trying to clear timer %p from "
                            "inside its handler %p.\n",
                            fibril_get_id(), timer, timer->fun);
                        abort();
                }

                fibril_condvar_wait(&timer->cv, timer->lockp);
        }

        old_state = timer->state;
        timer->state = fts_not_set;

        timer->delay = 0;
        timer->fun = NULL;
        timer->arg = NULL;
        fibril_condvar_broadcast(&timer->cv);

        return old_state;
}

/**
 * Initialize a semaphore with initial count set to the provided value.
 *
 * @param sem    Semaphore to initialize.
 * @param count  Initial count. Must not be negative.
 */
void fibril_semaphore_initialize(fibril_semaphore_t *sem, long count)
{
        /*
         * Negative count denotes the length of waitlist,
         * so it makes no sense as an initial value.
         */
        assert(count >= 0);
        sem->count = count;
        list_initialize(&sem->waiters);
}

/**
 * Produce one token.
 * If there are fibrils waiting for tokens, this operation satisfies
 * exactly one waiting `fibril_semaphore_down()`.
 * This operation never blocks the fibril.
 *
 * @param sem  Semaphore to use.
 */
void fibril_semaphore_up(fibril_semaphore_t *sem)
{
        futex_lock(&async_futex);
        sem->count++;

        if (sem->count > 0) {
                futex_unlock(&async_futex);
                return;
        }

        link_t *tmp = list_first(&sem->waiters);
        assert(tmp);
        list_remove(tmp);

        futex_unlock(&async_futex);

        awaiter_t *wdp = list_get_instance(tmp, awaiter_t, wu_event.link);
        fibril_add_ready(wdp->fid);
        optimize_execution_power();
}

/**
 * Consume one token.
 * If there are no available tokens (count <= 0), this operation blocks until
 * another fibril produces a token using `fibril_semaphore_up()`.
 *
 * @param sem  Semaphore to use.
 */
void fibril_semaphore_down(fibril_semaphore_t *sem)
{
        futex_lock(&async_futex);
        sem->count--;

        if (sem->count >= 0) {
                futex_unlock(&async_futex);
                return;
        }

        awaiter_t wdata;
        awaiter_initialize(&wdata);

        wdata.fid = fibril_get_id();
        list_append(&wdata.wu_event.link, &sem->waiters);

        fibril_switch(FIBRIL_FROM_BLOCKED);
        futex_unlock(&async_futex);
}

/** @}
 */