mpm_worker: follow up to r1783755.

Use a mutex for ptrans' allocator to be safe with concurrent
creation and destruction of its subpools, like with mod_http2.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1783808 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 27 insertions, 0 deletions

diff --git a/server/mpm/worker/worker.c b/server/mpm/worker/worker.c
index ed062b2abe..e3452c99a3 100644
--- a/server/mpm/worker/worker.c
+++ b/server/mpm/worker/worker.c
@@ -833,6 +833,8 @@ static void * APR_THREAD_FUNC listener_thread(apr_thread_t *thd, void * dummy)
         } /* if/else */
 
         if (!listener_may_exit) {
+            apr_thread_mutex_t *mutex;
+
             if (ptrans == NULL) {
                 /* we can't use a recycled transaction pool this time.
                  * create a new transaction pool */
@@ -844,6 +846,31 @@ static void * APR_THREAD_FUNC listener_thread(apr_thread_t *thd, void * dummy)
                 apr_allocator_owner_set(allocator, ptrans);
             }
             apr_pool_tag(ptrans, "transaction");
+
+            /* We need a mutex in the allocator to synchronize ptrans'
+             * children creations/destructions, but this mutex ought to
+             * live in ptrans itself to avoid leaks, hence it's cleared
+             * in ap_push_pool(). We could recycle some pconf's mutexes
+             * like we do for ptrans subpools, but that'd need another
+             * synchronization mechanism, whereas creating a pthread
+             * mutex (unix here!) is really as simple/fast as a static
+             * PTHREAD_MUTEX_INIT assignment, so let's not bother and
+             * create the mutex for each ptrans (recycled or not).
+             */
+            rv = apr_thread_mutex_create(&mutex,
+                                         APR_THREAD_MUTEX_DEFAULT,
+                                         ptrans);
+            if (rv != APR_SUCCESS) {
+                ap_log_error(APLOG_MARK, APLOG_CRIT, rv,
+                             ap_server_conf, APLOGNO(10019)
+                             "Failed to create transaction pool mutex");
+                resource_shortage = 1;
+                signal_threads(ST_GRACEFUL);
+                return NULL;
+            }
+            apr_allocator_mutex_set(apr_pool_allocator_get(ptrans),
+                                    mutex);
+
             rv = lr->accept_func(&csd, lr, ptrans);
             /* later we trash rv and rely on csd to indicate success/failure */
             AP_DEBUG_ASSERT(rv == APR_SUCCESS || !csd);