From b5b99e684e04d2ef9676eb08579e4fdfc14ca6a0 Mon Sep 17 00:00:00 2001
From: Paolo Amadini <paolo.mozmail@amadzone.org>
Date: Thu, 6 Nov 2014 14:00:06 +0000
Subject: [PATCH] Bug 1094248 - Process remaining Promise microtasks before
 blocking inside a nested event loop in the main thread. r=bz

---
 js/xpconnect/src/nsXPConnect.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/js/xpconnect/src/nsXPConnect.cpp b/js/xpconnect/src/nsXPConnect.cpp
index cba5414e2c9a..049557815087 100644
--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -1026,6 +1026,13 @@ NS_IMETHODIMP
 nsXPConnect::OnProcessNextEvent(nsIThreadInternal *aThread, bool aMayWait,
                                 uint32_t aRecursionDepth)
 {
+    // If ProcessNextEvent was called during a Promise "then" callback, we
+    // must process any pending microtasks before blocking in the event loop,
+    // otherwise we may deadlock until an event enters the queue later.
+    if (aMayWait) {
+        Promise::PerformMicroTaskCheckpoint();
+    }
+
     // Record this event.
     mEventDepth++;