Break out of epoll_wait when adding loop callbacks during event loop

folly/io/async/EventBase.cpp

@@ -851,29 +851,36 @@ void EventBase::terminateLoopSoon() {
   queue_->putMessage([] {});
 }
 
+void EventBase::addLoopCallback(LoopCallback& callback, bool thisIteration) {
+  if (runOnceCallbacks_ != nullptr && thisIteration) {
+    runOnceCallbacks_->push_back(callback);
+  } else {
+    loopCallbacks_.push_back(callback);
+    // If we're adding to loopCallbacks_ while the loop is running (but not
+    // inside runLoopCallbacks), we need to break out of eb_event_base_loop()
+    // so the callback can be processed promptly. Otherwise the loop may be
+    // blocked in epoll_wait and won't process the callback until it times out.
+    if (isRunning()) {
+      evb_->eb_event_base_loopbreak();
+    }
+  }
+}
+
 void EventBase::runInLoop(
     LoopCallback* callback,
     bool thisIteration,
     std::shared_ptr<RequestContext> rctx) {
   dcheckIsInEventBaseThread();
   callback->cancelLoopCallback();
   callback->context_ = std::move(rctx);
-  if (runOnceCallbacks_ != nullptr && thisIteration) {
-    runOnceCallbacks_->push_back(*callback);
-  } else {
-    loopCallbacks_.push_back(*callback);
-  }
+  addLoopCallback(*callback, thisIteration);
 }
 
 void EventBase::runInLoop(Func cob, bool thisIteration) {
   dcheckIsInEventBaseThread();
   auto wrapper = new FunctionLoopCallback(std::move(cob));
   wrapper->context_ = RequestContext::saveContext();
-  if (runOnceCallbacks_ != nullptr && thisIteration) {
-    runOnceCallbacks_->push_back(*wrapper);
-  } else {
-    loopCallbacks_.push_back(*wrapper);
-  }
+  addLoopCallback(*wrapper, thisIteration);
 }
 
 void EventBase::runOnDestruction(OnDestructionCallback& callback) {

folly/io/async/EventBase.h

@@ -1047,6 +1047,10 @@ class EventBase
       LoopCallbackList& currentCallbacks,
       const LoopCallbacksDeadline& deadline);
 
+  // Helper to add a callback to the appropriate list (runOnceCallbacks_ or
+  // loopCallbacks_) and break out of epoll_wait if needed.
+  void addLoopCallback(LoopCallback& callback, bool thisIteration);
+
   // executes any callbacks queued by runInLoop(); returns false if none found
   bool runLoopCallbacks();