semaphore.c

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/*
 * Copyright (c) 2014, Michael Müller
 * Copyright (c) 2014, Sebastian Lackner
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER OR CONTRIBUTORS 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 <process/semaphore.h>
#include <process/object.h>
#include <memory/allocator.h>
#include <util/list.h>
#include <util/util.h>

static void __semaphoreDestroy(struct object *obj);
static void __semaphoreShutdown(struct object *obj, UNUSED uint32_t mode);
static int32_t __semaphoreGetStatus(struct object *obj, UNUSED uint32_t mode);
static struct linkedList *__semaphoreWait(struct object *obj, UNUSED uint32_t mode, uint32_t *result);
static void __semaphoreSignal(struct object *obj, UNUSED uint32_t result);

static const struct objectFunctions semaphoreFunctions =
{
    __semaphoreDestroy,
    NULL, /* getMinHandle */
    __semaphoreShutdown,
    __semaphoreGetStatus,
    __semaphoreWait,
    __semaphoreSignal,
    NULL, /* write */
    NULL, /* read */
    NULL, /* insert */
    NULL, /* remove */
};

struct semaphore *semaphoreCreate(uint32_t value)
{
    struct semaphore *s;

    /* allocate some new memory */
    if (!(s = heapAlloc(sizeof(*s))))
        return NULL;

    /* initialize general object info */
    __objectInit(&s->obj, &semaphoreFunctions);
    ll_init(&s->waiters);
    s->value = value;

    return s;
}

static void __semaphoreDestroy(struct object *obj)
{
    struct semaphore *s = objectContainer(obj, struct semaphore, &semaphoreFunctions);

    /* release other threads if the user destroys the object before they return */
    queueWakeup(&s->waiters, true, -1);
    assert(ll_empty(&s->waiters));

    /* release semaphore memory */
    s->obj.functions = NULL;
    heapFree(s);
}

static void __semaphoreShutdown(struct object *obj, UNUSED uint32_t mode)
{
    struct semaphore *s = objectContainer(obj, struct semaphore, &semaphoreFunctions);
    queueWakeup(&s->waiters, true, -1);
}

static int32_t __semaphoreGetStatus(struct object *obj, UNUSED uint32_t mode)
{
    struct semaphore *s = objectContainer(obj, struct semaphore, &semaphoreFunctions);
    return s->value;
}

static struct linkedList *__semaphoreWait(struct object *obj, UNUSED uint32_t mode, uint32_t *result)
{
    struct semaphore *s = objectContainer(obj, struct semaphore, &semaphoreFunctions);
    if (s->value == 0) return &s->waiters;

    *result = --s->value;
    return NULL;
}

static void __semaphoreSignal(struct object *obj, UNUSED uint32_t result)
{
    struct semaphore *s = objectContainer(obj, struct semaphore, &semaphoreFunctions);
    if (ll_empty(&s->waiters))
        s->value++;
    else
    {
        assert(s->value == 0);
        queueWakeup(&s->waiters, false, 0);
    }
}