source: mainline/uspace/lib/libc/generic/fibril_sync.c@ b6ee5b1

/*
 * 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_sync.h>
#include <fibril.h>
#include <async.h>
#include <adt/list.h>
#include <futex.h>
#include <assert.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.
         */
        if (atomic_get(&threads_in_ipc_wait) > 0)
                ipc_poke();
}

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

void fibril_mutex_lock(fibril_mutex_t *fm)
{
        futex_down(&async_futex);
        if (fm->counter-- <= 0) {
                fibril_t *f = (fibril_t *) fibril_get_id();
                list_append(&f->link, &fm->waiters);
                fibril_switch(FIBRIL_TO_MANAGER);
        } else {
                futex_up(&async_futex);
        }
}

bool fibril_mutex_trylock(fibril_mutex_t *fm)
{
        bool locked = false;
        
        futex_down(&async_futex);
        if (fm->counter > 0) {
                fm->counter--;
                locked = true;
        }
        futex_up(&async_futex);
        
        return locked;
}

static void _fibril_mutex_unlock_unsafe(fibril_mutex_t *fm)
{
        assert(fm->counter <= 0);
        if (fm->counter++ < 0) {
                link_t *tmp;
                fibril_t *f;
        
                assert(!list_empty(&fm->waiters));
                tmp = fm->waiters.next;
                f = list_get_instance(tmp, fibril_t, link);
                list_remove(&f->link);
                fibril_add_ready((fid_t) f);
                optimize_execution_power();
        }
}

void fibril_mutex_unlock(fibril_mutex_t *fm)
{
        futex_down(&async_futex);
        _fibril_mutex_unlock_unsafe(fm);
        futex_up(&async_futex);
}

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

void fibril_rwlock_read_lock(fibril_rwlock_t *frw)
{
        futex_down(&async_futex);
        if (frw->writers) {
                fibril_t *f = (fibril_t *) fibril_get_id();
                f->flags &= ~FIBRIL_WRITER;
                list_append(&f->link, &frw->waiters);
                fibril_switch(FIBRIL_TO_MANAGER);
        } else {
                frw->readers++;
                futex_up(&async_futex);
        }
}

void fibril_rwlock_write_lock(fibril_rwlock_t *frw)
{
        futex_down(&async_futex);
        if (frw->writers || frw->readers) {
                fibril_t *f = (fibril_t *) fibril_get_id();
                f->flags |= FIBRIL_WRITER;
                list_append(&f->link, &frw->waiters);
                fibril_switch(FIBRIL_TO_MANAGER);
        } else {
                frw->writers++;
                futex_up(&async_futex);
        }
}

static void _fibril_rwlock_common_unlock(fibril_rwlock_t *frw)
{
        futex_down(&async_futex);
        assert(frw->readers || (frw->writers == 1));
        if (frw->readers) {
                if (--frw->readers)
                        goto out;
        } else {
                frw->writers--;
        }
        
        assert(!frw->readers && !frw->writers);
        
        while (!list_empty(&frw->waiters)) {
                link_t *tmp = frw->waiters.next;
                fibril_t *f = list_get_instance(tmp, fibril_t, link);
                
                if (f->flags & FIBRIL_WRITER) {
                        if (frw->readers)
                                break;
                        list_remove(&f->link);
                        fibril_add_ready((fid_t) f);
                        frw->writers++;
                        optimize_execution_power();
                        break;
                } else {
                        list_remove(&f->link);
                        fibril_add_ready((fid_t) f);
                        frw->readers++;
                        optimize_execution_power();
                }
        }
out:
        futex_up(&async_futex);
}

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

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

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

void fibril_condvar_wait(fibril_condvar_t *fcv, fibril_mutex_t *fm)
{
        fibril_t *f = (fibril_t *) fibril_get_id();

        futex_down(&async_futex);
        list_append(&f->link, &fcv->waiters);
        _fibril_mutex_unlock_unsafe(fm);
        fibril_switch(FIBRIL_TO_MANAGER);
        fibril_mutex_lock(fm);
}

static void _fibril_condvar_wakeup_common(fibril_condvar_t *fcv, bool once)
{
        link_t *tmp;
        fibril_t *f;

        futex_down(&async_futex);
        while (!list_empty(&fcv->waiters)) {
                tmp = fcv->waiters.next;
                f = list_get_instance(tmp, fibril_t, link);
                list_remove(&f->link);
                fibril_add_ready((fid_t) f);
                optimize_execution_power();
                if (once)
                        break;
        }
        futex_up(&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);
}

/** @}
 */