evwatch: fix race condition

There was a race between event_base_loop and evwatch_new (adding a
prepare/check watcher while iterating over the watcher list). Only
release the mutex immediately before invoking each watcher callback,
and reacquire it immediately afterwards (same as is done for normal
event handlers).

1 files changed, 8 insertions, 6 deletions

diff --git a/event.c b/event.c
index 34f28ba2..a82d5094 100644
--- a/event.c
+++ b/event.c
@@ -2006,11 +2006,12 @@ event_base_loop(struct event_base *base, int flags)
 		event_queue_make_later_events_active(base);
 
 		/* Invoke prepare watchers before polling for events */
-		EVBASE_RELEASE_LOCK(base, th_base_lock);
 		prepare_info.timeout = tv_p;
-		TAILQ_FOREACH(watcher, &base->watchers[EVWATCH_PREPARE], next)
+		TAILQ_FOREACH(watcher, &base->watchers[EVWATCH_PREPARE], next) {
+			EVBASE_RELEASE_LOCK(base, th_base_lock);
 			(*watcher->callback.prepare)(watcher, &prepare_info, watcher->arg);
-		EVBASE_ACQUIRE_LOCK(base, th_base_lock);
+			EVBASE_ACQUIRE_LOCK(base, th_base_lock);
+		}
 
 		clear_time_cache(base);
 
@@ -2027,10 +2028,11 @@ event_base_loop(struct event_base *base, int flags)
 
 		/* Invoke check watchers after polling for events, and before
 		 * processing them */
-		EVBASE_RELEASE_LOCK(base, th_base_lock);
-		TAILQ_FOREACH(watcher, &base->watchers[EVWATCH_CHECK], next)
+		TAILQ_FOREACH(watcher, &base->watchers[EVWATCH_CHECK], next) {
+			EVBASE_RELEASE_LOCK(base, th_base_lock);
 			(*watcher->callback.check)(watcher, &check_info, watcher->arg);
-		EVBASE_ACQUIRE_LOCK(base, th_base_lock);
+			EVBASE_ACQUIRE_LOCK(base, th_base_lock);
+		}
 
 		timeout_process(base);