/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "fdqueue.h"

struct fd_queue_info_t {
    int idlers;
    apr_thread_mutex_t *idlers_mutex;
    apr_thread_cond_t *wait_for_idler;
    int terminated;
    int max_idlers;
    apr_pool_t        **recycled_pools;
    int num_recycled;
};

static apr_status_t queue_info_cleanup(void *data_)
{
    fd_queue_info_t *qi = data_;
    int i;
    apr_thread_cond_destroy(qi->wait_for_idler);
    apr_thread_mutex_destroy(qi->idlers_mutex);
    for (i = 0; i < qi->num_recycled; i++) {
        apr_pool_destroy(qi->recycled_pools[i]);
    }
    return APR_SUCCESS;
}

apr_status_t ap_queue_info_create(fd_queue_info_t **queue_info,
                                  apr_pool_t *pool, int max_idlers)
{
    apr_status_t rv;
    fd_queue_info_t *qi;

    qi = apr_palloc(pool, sizeof(*qi));
    memset(qi, 0, sizeof(*qi));

    rv = apr_thread_mutex_create(&qi->idlers_mutex, APR_THREAD_MUTEX_DEFAULT,
                                 pool);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    rv = apr_thread_cond_create(&qi->wait_for_idler, pool);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    qi->recycled_pools = (apr_pool_t **)apr_palloc(pool, max_idlers *
                                                   sizeof(apr_pool_t *));
    qi->num_recycled = 0;
    qi->max_idlers = max_idlers;
    apr_pool_cleanup_register(pool, qi, queue_info_cleanup,
                              apr_pool_cleanup_null);

    *queue_info = qi;

    return APR_SUCCESS;
}

apr_status_t ap_queue_info_set_idle(fd_queue_info_t *queue_info,
                                    apr_pool_t *pool_to_recycle)
{
    apr_status_t rv;
    rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    AP_DEBUG_ASSERT(queue_info->idlers >= 0);
    AP_DEBUG_ASSERT(queue_info->num_recycled < queue_info->max_idlers);
    if (pool_to_recycle) {
        queue_info->recycled_pools[queue_info->num_recycled++] =
            pool_to_recycle;
    }
    if (queue_info->idlers++ == 0) {
        /* Only signal if we had no idlers before. */
        apr_thread_cond_signal(queue_info->wait_for_idler);
    }
    rv = apr_thread_mutex_unlock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    return APR_SUCCESS;
}

apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t *queue_info,
                                          apr_pool_t **recycled_pool)
{
    apr_status_t rv;
    *recycled_pool = NULL;
    rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    AP_DEBUG_ASSERT(queue_info->idlers >= 0);
    while ((queue_info->idlers == 0) && (!queue_info->terminated)) {
        rv = apr_thread_cond_wait(queue_info->wait_for_idler,
                                  queue_info->idlers_mutex);
        if (rv != APR_SUCCESS) {
            apr_status_t rv2;
            rv2 = apr_thread_mutex_unlock(queue_info->idlers_mutex);
            if (rv2 != APR_SUCCESS) {
                return rv2;
            }
            return rv;
        }
    }
    queue_info->idlers--; /* Oh, and idler? Let's take 'em! */
    if (queue_info->num_recycled) {
        *recycled_pool =
            queue_info->recycled_pools[--queue_info->num_recycled];
    }
    rv = apr_thread_mutex_unlock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    else if (queue_info->terminated) {
        return APR_EOF;
    }
    else {
        return APR_SUCCESS;
    }
}

apr_status_t ap_queue_info_term(fd_queue_info_t *queue_info)
{
    apr_status_t rv;
    rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    queue_info->terminated = 1;
    apr_thread_cond_broadcast(queue_info->wait_for_idler);
    rv = apr_thread_mutex_unlock(queue_info->idlers_mutex);
    if (rv != APR_SUCCESS) {
        return rv;
    }
    return APR_SUCCESS;
}

/**
 * Detects when the fd_queue_t is full. This utility function is expected
 * to be called from within critical sections, and is not threadsafe.
 */
#define ap_queue_full(queue) ((queue)->nelts == (queue)->bounds)

/**
 * Detects when the fd_queue_t is empty. This utility function is expected
 * to be called from within critical sections, and is not threadsafe.
 */
#define ap_queue_empty(queue) ((queue)->nelts == 0)

/**
 * Callback routine that is called to destroy this
 * fd_queue_t when its pool is destroyed.
 */
static apr_status_t ap_queue_destroy(void *data) 
{
    fd_queue_t *queue = data;

    /* Ignore errors here, we can't do anything about them anyway.
     * XXX: We should at least try to signal an error here, it is
     * indicative of a programmer error. -aaron */
    apr_thread_cond_destroy(queue->not_empty);
    apr_thread_mutex_destroy(queue->one_big_mutex);

    return APR_SUCCESS;
}

/**
 * Initialize the fd_queue_t.
 */
apr_status_t ap_queue_init(fd_queue_t *queue, int queue_capacity, apr_pool_t *a)
{
    int i;
    apr_status_t rv;

    if ((rv = apr_thread_mutex_create(&queue->one_big_mutex,
                                      APR_THREAD_MUTEX_DEFAULT, a)) != APR_SUCCESS) {
        return rv;
    }
    if ((rv = apr_thread_cond_create(&queue->not_empty, a)) != APR_SUCCESS) {
        return rv;
    }

    queue->data = apr_palloc(a, queue_capacity * sizeof(fd_queue_elem_t));
    queue->bounds = queue_capacity;
    queue->nelts = 0;

    /* Set all the sockets in the queue to NULL */
    for (i = 0; i < queue_capacity; ++i)
        queue->data[i].sd = NULL;

    apr_pool_cleanup_register(a, queue, ap_queue_destroy, apr_pool_cleanup_null);

    return APR_SUCCESS;
}

/**
 * Push a new socket onto the queue. Blocks if the queue is full. Once
 * the push operation has completed, it signals other threads waiting
 * in ap_queue_pop() that they may continue consuming sockets.
 */
apr_status_t ap_queue_push(fd_queue_t *queue, apr_socket_t *sd, apr_pool_t *p)
{
    fd_queue_elem_t *elem;
    apr_status_t rv;

    if ((rv = apr_thread_mutex_lock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }

    AP_DEBUG_ASSERT(!queue->terminated);
    AP_DEBUG_ASSERT(!ap_queue_full(queue));

    elem = &queue->data[queue->nelts];
    elem->sd = sd;
    elem->p = p;
    queue->nelts++;

    apr_thread_cond_signal(queue->not_empty);

    if ((rv = apr_thread_mutex_unlock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }

    return APR_SUCCESS;
}

/**
 * Retrieves the next available socket from the queue. If there are no
 * sockets available, it will block until one becomes available.
 * Once retrieved, the socket is placed into the address specified by
 * 'sd'.
 */
apr_status_t ap_queue_pop(fd_queue_t *queue, apr_socket_t **sd, apr_pool_t **p)
{
    fd_queue_elem_t *elem;
    apr_status_t rv;

    if ((rv = apr_thread_mutex_lock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }

    /* Keep waiting until we wake up and find that the queue is not empty. */
    if (ap_queue_empty(queue)) {
        if (!queue->terminated) {
            apr_thread_cond_wait(queue->not_empty, queue->one_big_mutex);
        }
        /* If we wake up and it's still empty, then we were interrupted */
        if (ap_queue_empty(queue)) {
            rv = apr_thread_mutex_unlock(queue->one_big_mutex);
            if (rv != APR_SUCCESS) {
                return rv;
            }
            if (queue->terminated) {
                return APR_EOF; /* no more elements ever again */
            }
            else {
                return APR_EINTR;
            }
        }
    } 

    elem = &queue->data[--queue->nelts];
    *sd = elem->sd;
    *p = elem->p;
#ifdef AP_DEBUG
    elem->sd = NULL;
    elem->p = NULL;
#endif /* AP_DEBUG */

    rv = apr_thread_mutex_unlock(queue->one_big_mutex);
    return rv;
}

apr_status_t ap_queue_interrupt_all(fd_queue_t *queue)
{
    apr_status_t rv;
    
    if ((rv = apr_thread_mutex_lock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }
    apr_thread_cond_broadcast(queue->not_empty);
    if ((rv = apr_thread_mutex_unlock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }
    return APR_SUCCESS;
}

apr_status_t ap_queue_term(fd_queue_t *queue)
{
    apr_status_t rv;

    if ((rv = apr_thread_mutex_lock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }
    /* we must hold one_big_mutex when setting this... otherwise,
     * we could end up setting it and waking everybody up just after a 
     * would-be popper checks it but right before they block
     */
    queue->terminated = 1;
    if ((rv = apr_thread_mutex_unlock(queue->one_big_mutex)) != APR_SUCCESS) {
        return rv;
    }
    return ap_queue_interrupt_all(queue);
}