/* 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 "mpm_fdqueue.h"
#if APR_HAS_THREADS
#include <apr_atomic.h>
static const apr_uint32_t zero_pt = APR_UINT32_MAX/2;
struct recycled_pool
{
apr_pool_t *pool;
struct recycled_pool *next;
};
struct fd_queue_info_t
{
apr_uint32_t volatile idlers; /**
* >= zero_pt: number of idle worker threads
* < zero_pt: number of threads blocked,
* waiting for an idle worker
*/
apr_thread_mutex_t *idlers_mutex;
apr_thread_cond_t *wait_for_idler;
int terminated;
int max_idlers;
int max_recycled_pools;
apr_uint32_t recycled_pools_count;
struct recycled_pool *volatile recycled_pools;
};
struct fd_queue_elem_t
{
apr_socket_t *sd;
void *sd_baton;
apr_pool_t *p;
};
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((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,
int max_recycled_pools)
{
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_recycled_pools = max_recycled_pools;
qi->max_idlers = max_idlers;
qi->idlers = zero_pt;
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;
ap_queue_info_push_pool(queue_info, pool_to_recycle);
/* If other threads are waiting on a worker, wake one up */
if (apr_atomic_inc32(&queue_info->idlers) < zero_pt) {
rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
AP_DEBUG_ASSERT(0);
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_try_get_idler(fd_queue_info_t *queue_info)
{
/* Don't block if there isn't any idle worker. */
for (;;) {
apr_uint32_t idlers = queue_info->idlers;
if (idlers <= zero_pt) {
return APR_EAGAIN;
}
if (apr_atomic_cas32(&queue_info->idlers, idlers - 1,
idlers) == idlers) {
return APR_SUCCESS;
}
}
}
apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t *queue_info,
int *had_to_block)
{
apr_status_t rv;
/* Block if there isn't any idle worker.
* apr_atomic_add32(x, -1) does the same as dec32(x), except
* that it returns the previous value (unlike dec32's bool).
*/
if (apr_atomic_add32(&queue_info->idlers, -1) <= zero_pt) {
rv = apr_thread_mutex_lock(queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
AP_DEBUG_ASSERT(0);
apr_atomic_inc32(&(queue_info->idlers)); /* back out dec */
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 negative, the
* workers are all still busy, so it's safe to
* block on a condition variable.
* - If the idle worker count is non-negative, 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 non-negative, it's safe for this function to
* return immediately.
*
* A "negative value" (relative to zero_pt) in
* queue_info->idlers tells how many
* threads are waiting on an idle worker.
*/
if (queue_info->idlers < zero_pt) {
if (had_to_block) {
*had_to_block = 1;
}
rv = apr_thread_cond_wait(queue_info->wait_for_idler,
queue_info->idlers_mutex);
if (rv != APR_SUCCESS) {
AP_DEBUG_ASSERT(0);
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;
}
}
if (queue_info->terminated) {
return APR_EOF;
}
else {
return APR_SUCCESS;
}
}
apr_uint32_t ap_queue_info_num_idlers(fd_queue_info_t *queue_info)
{
apr_uint32_t val;
val = apr_atomic_read32(&queue_info->idlers);
return (val > zero_pt) ? val - zero_pt : 0;
}
void ap_queue_info_push_pool(fd_queue_info_t *queue_info,
apr_pool_t *pool_to_recycle)
{
struct recycled_pool *new_recycle;
/* 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)
return;
if (queue_info->max_recycled_pools >= 0) {
apr_uint32_t n = apr_atomic_read32(&queue_info->recycled_pools_count);
if (n >= queue_info->max_recycled_pools) {
apr_pool_destroy(pool_to_recycle);
return;
}
apr_atomic_inc32(&queue_info->recycled_pools_count);
}
apr_pool_clear(pool_to_recycle);
new_recycle = 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((void *)&queue_info->recycled_pools,
new_recycle, next) == next)
break;
}
}
void ap_queue_info_pop_pool(fd_queue_info_t *queue_info,
apr_pool_t **recycled_pool)
{
/* 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.
*/
*recycled_pool = NULL;
/* Atomically pop a pool from the recycled list */
for (;;) {
struct recycled_pool *first_pool = queue_info->recycled_pools;
if (first_pool == NULL) {
break;
}
if (apr_atomic_casptr((void *)&queue_info->recycled_pools,
first_pool->next, first_pool) == first_pool) {
*recycled_pool = first_pool->pool;
if (queue_info->max_recycled_pools >= 0)
apr_atomic_dec32(&queue_info->recycled_pools_count);
break;
}
}
}
void ap_queue_info_free_idle_pools(fd_queue_info_t *queue_info)
{
apr_pool_t *p;
queue_info->max_recycled_pools = 0;
for (;;) {
ap_queue_info_pop_pool(queue_info, &p);
if (p == NULL)
break;
apr_pool_destroy(p);
}
apr_atomic_set32(&queue_info->recycled_pools_count, 0);
}
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 && \
APR_RING_EMPTY(&queue->timers, \
timer_event_t, link))
/**
* 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_create(fd_queue_t **pqueue, int capacity, apr_pool_t *p)
{
apr_status_t rv;
fd_queue_t *queue;
queue = apr_pcalloc(p, sizeof *queue);
if ((rv = apr_thread_mutex_create(&queue->one_big_mutex,
APR_THREAD_MUTEX_DEFAULT,
p)) != APR_SUCCESS) {
return rv;
}
if ((rv = apr_thread_cond_create(&queue->not_empty, p)) != APR_SUCCESS) {
return rv;
}
APR_RING_INIT(&queue->timers, timer_event_t, link);
queue->data = apr_pcalloc(p, capacity * sizeof(fd_queue_elem_t));
queue->bounds = capacity;
apr_pool_cleanup_register(p, queue, ap_queue_destroy,
apr_pool_cleanup_null);
*pqueue = queue;
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_socket(fd_queue_t *queue,
apr_socket_t *sd, void *sd_baton,
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->in++];
if (queue->in >= queue->bounds)
queue->in -= queue->bounds;
elem->sd = sd;
elem->sd_baton = sd_baton;
elem->p = p;
queue->nelts++;
apr_thread_cond_signal(queue->not_empty);
return apr_thread_mutex_unlock(queue->one_big_mutex);
}
apr_status_t ap_queue_push_timer(fd_queue_t *queue, timer_event_t *te)
{
apr_status_t rv;
if ((rv = apr_thread_mutex_lock(queue->one_big_mutex)) != APR_SUCCESS) {
return rv;
}
AP_DEBUG_ASSERT(!queue->terminated);
APR_RING_INSERT_TAIL(&queue->timers, te, timer_event_t, link);
apr_thread_cond_signal(queue->not_empty);
return apr_thread_mutex_unlock(queue->one_big_mutex);
}
/**
* 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_something(fd_queue_t *queue,
apr_socket_t **sd, void **sd_baton,
apr_pool_t **p, timer_event_t **te_out)
{
fd_queue_elem_t *elem;
timer_event_t *te;
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;
}
}
}
te = NULL;
if (te_out) {
if (!APR_RING_EMPTY(&queue->timers, timer_event_t, link)) {
te = APR_RING_FIRST(&queue->timers);
APR_RING_REMOVE(te, link);
}
*te_out = te;
}
if (!te) {
elem = &queue->data[queue->out++];
if (queue->out >= queue->bounds)
queue->out -= queue->bounds;
queue->nelts--;
*sd = elem->sd;
if (sd_baton) {
*sd_baton = elem->sd_baton;
}
*p = elem->p;
#ifdef AP_DEBUG
elem->sd = NULL;
elem->p = NULL;
#endif /* AP_DEBUG */
}
return apr_thread_mutex_unlock(queue->one_big_mutex);
}
static apr_status_t queue_interrupt(fd_queue_t *queue, int all, int term)
{
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
*/
if (term) {
queue->terminated = 1;
}
if (all)
apr_thread_cond_broadcast(queue->not_empty);
else
apr_thread_cond_signal(queue->not_empty);
return apr_thread_mutex_unlock(queue->one_big_mutex);
}
apr_status_t ap_queue_interrupt_all(fd_queue_t *queue)
{
return queue_interrupt(queue, 1, 0);
}
apr_status_t ap_queue_interrupt_one(fd_queue_t *queue)
{
return queue_interrupt(queue, 0, 0);
}
apr_status_t ap_queue_term(fd_queue_t *queue)
{
return queue_interrupt(queue, 1, 1);
}
#endif /* APR_HAS_THREADS */