void ap_pop_pool(apr_pool_t ** recycled_pool, fd_queue_info_t * queue_info)
{
/* 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;
}
}
}
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((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;
}
static void test_casptr_notequal(abts_case *tc, void *data)
{
int a, b;
volatile void *target_ptr = &a;
void *old_ptr;
old_ptr = apr_atomic_casptr(&target_ptr, &a, &b);
ABTS_PTR_EQUAL(tc, &a, old_ptr);
ABTS_PTR_EQUAL(tc, &a, (void *) target_ptr);
}
static void test_casptr_equal(abts_case *tc, void *data)
{
int a;
volatile void *target_ptr = NULL;
void *old_ptr;
old_ptr = apr_atomic_casptr(&target_ptr, &a, NULL);
ABTS_PTR_EQUAL(tc, NULL, old_ptr);
ABTS_PTR_EQUAL(tc, &a, (void *) target_ptr);
}
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;
}
void ap_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 cnt = apr_atomic_read32(&queue_info->recycled_pools_count);
if (cnt >= 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 = (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((void*) &(queue_info->recycled_pools),
new_recycle, next) == next)
break;
}
}
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, BUT
* we need to check for idle worker count again
* when we are signaled since it can happen that
* we are signaled by a worker thread that went idle
* but received a context switch before it could
* tell us. If it does signal us later once it is on
* CPU again there might be no idle worker left.
* See
* https://issues.apache.org/bugzilla/show_bug.cgi?id=45605#c4
* - 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.
*/
while (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((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_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 */
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;
}
}
void* apr_atomic_casptr_wrapper(volatile void** mem,
void* with, const void *cmp) {
void* ret = apr_atomic_casptr(mem, with, cmp);
NoiseMaker(2,0);
return ret;
}
