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DEFINITIONS
This source file includes following definitions.
- queue_info_cleanup
- ap_queue_info_create
- ap_queue_info_set_idle
- ap_queue_info_wait_for_idler
- ap_queue_info_term
- ap_queue_destroy
- ap_queue_init
- ap_queue_push
- ap_queue_pop
- ap_queue_interrupt_all
- ap_queue_term
/* 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"
#include "apr_atomic.h"
typedef struct recycled_pool {
apr_pool_t *pool;
struct recycled_pool *next;
} recycled_pool;
struct fd_queue_info_t {
apr_uint32_t idlers;
apr_thread_mutex_t *idlers_mutex;
apr_thread_cond_t *wait_for_idler;
int terminated;
int max_idlers;
recycled_pool *recycled_pools;
};
static apr_status_t queue_info_cleanup(void *data_)
{
fd_queue_info_t *qi = data_;
apr_thread_cond_destroy(qi->wait_for_idler);
apr_thread_mutex_destroy(qi->idlers_mutex);
/* Clean up any pools in the recycled list */
for (;;) {
struct recycled_pool *first_pool = qi->recycled_pools;
if (first_pool == NULL) {
break;
}
if (apr_atomic_casptr((volatile void**)&(qi->recycled_pools), first_pool->next,
first_pool) == first_pool) {
apr_pool_destroy(first_pool->pool);
}
}
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_pcalloc(pool, 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 = NULL;
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;
int prev_idlers;
/* If we have been given a pool to recycle, atomically link
* it into the queue_info's list of recycled pools
*/
if (pool_to_recycle) {
struct recycled_pool *new_recycle;
new_recycle = (struct recycled_pool *)apr_palloc(pool_to_recycle,
sizeof(*new_recycle));
new_recycle->pool = pool_to_recycle;
for (;;) {
/* Save queue_info->recycled_pool in local variable next because
* new_recycle->next can be changed after apr_atomic_casptr
* function call. For gory details see PR 44402.
*/
struct recycled_pool *next = queue_info->recycled_pools;
new_recycle->next = next;
if (apr_atomic_casptr((volatile void**)&(queue_info->recycled_pools),
new_recycle, next) == next) {
break;
}
}
}
/* Atomically increment the count of idle workers */
for (;;) {
prev_idlers = queue_info->idlers;
if (apr_atomic_cas32(&(queue_info->idlers), prev_idlers + 1,
prev_idlers) == prev_idlers) {
break;
}
}
/* If this thread just made the idle worker count nonzero,
* wake up the listener. */
if (prev_idlers == 0) {
rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
return rv;
}
rv = apr_thread_cond_signal(queue_info->wait_for_idler);
if (rv != APR_SUCCESS) {
apr_thread_mutex_unlock(queue_info->idlers_mutex);
return rv;
}
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;
/* Block if the count of idle workers is zero */
if (queue_info->idlers == 0) {
rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
return rv;
}
/* Re-check the idle worker count to guard against a
* race condition. Now that we're in the mutex-protected
* region, one of two things may have happened:
* - If the idle worker count is still zero, the
* workers are all still busy, so it's safe to
* block on a condition variable.
* - If the idle worker count is nonzero, then a
* worker has become idle since the first check
* of queue_info->idlers above. It's possible
* that the worker has also signaled the condition
* variable--and if so, the listener missed it
* because it wasn't yet blocked on the condition
* variable. But if the idle worker count is
* now nonzero, it's safe for this function to
* return immediately.
*/
if (queue_info->idlers == 0) {
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;
}
}
rv = apr_thread_mutex_unlock(queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
return rv;
}
}
/* Atomically decrement the idle worker count */
apr_atomic_dec32(&(queue_info->idlers));
/* Atomically pop a pool from the recycled list */
/* This function is safe only as long as it is single threaded because
* it reaches into the queue and accesses "next" which can change.
* We are OK today because it is only called from the listener thread.
* cas-based pushes do not have the same limitation - any number can
* happen concurrently with a single cas-based pop.
*/
for (;;) {
struct recycled_pool *first_pool = queue_info->recycled_pools;
if (first_pool == NULL) {
break;
}
if (apr_atomic_casptr((volatile void**)&(queue_info->recycled_pools), first_pool->next,
first_pool) == first_pool) {
*recycled_pool = first_pool->pool;
break;
}
}
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);
return apr_thread_mutex_unlock(queue_info->idlers_mutex);
}
/**
* 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.
*
* precondition: ap_queue_info_wait_for_idler has already been called
* to reserve an idle worker thread
*/
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);
return apr_thread_mutex_unlock(queue->one_big_mutex);
}
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);
}