diff -r 000000000000 -r 6474c204b198 xpcom/threads/nsEventQueue.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/threads/nsEventQueue.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,127 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsEventQueue.h"
+#include "nsAutoPtr.h"
+#include "prlog.h"
+#include "nsThreadUtils.h"
+#include "prthread.h"
+#include "mozilla/ChaosMode.h"
+
+using namespace mozilla;
+
+#ifdef PR_LOGGING
+static PRLogModuleInfo *
+GetLog()
+{
+  static PRLogModuleInfo *sLog;
+  if (!sLog)
+    sLog = PR_NewLogModule("nsEventQueue");
+  return sLog;
+}
+#endif
+#ifdef LOG
+#undef LOG
+#endif
+#define LOG(args) PR_LOG(GetLog(), PR_LOG_DEBUG, args)
+
+nsEventQueue::nsEventQueue()
+  : mReentrantMonitor("nsEventQueue.mReentrantMonitor")
+  , mHead(nullptr)
+  , mTail(nullptr)
+  , mOffsetHead(0)
+  , mOffsetTail(0)
+{
+}
+
+nsEventQueue::~nsEventQueue()
+{
+  // It'd be nice to be able to assert that no one else is holding the monitor,
+  // but NSPR doesn't really expose APIs for it.
+  NS_ASSERTION(IsEmpty(), "Non-empty event queue being destroyed; events being leaked.");
+
+  if (mHead)
+    FreePage(mHead);
+}
+
+bool
+nsEventQueue::GetEvent(bool mayWait, nsIRunnable **result)
+{
+  {
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+    
+    while (IsEmpty()) {
+      if (!mayWait) {
+        if (result)
+          *result = nullptr;
+        return false;
+      }
+      LOG(("EVENTQ(%p): wait begin\n", this)); 
+      mon.Wait();
+      LOG(("EVENTQ(%p): wait end\n", this)); 
+    }
+    
+    if (result) {
+      *result = mHead->mEvents[mOffsetHead++];
+      
+      // Check if mHead points to empty Page
+      if (mOffsetHead == EVENTS_PER_PAGE) {
+        Page *dead = mHead;
+        mHead = mHead->mNext;
+        FreePage(dead);
+        mOffsetHead = 0;
+      }
+    }
+  }
+
+  return true;
+}
+
+bool
+nsEventQueue::PutEvent(nsIRunnable *runnable)
+{
+  // Avoid calling AddRef+Release while holding our monitor.
+  nsRefPtr<nsIRunnable> event(runnable);
+  bool rv = true;
+  {
+    if (ChaosMode::isActive()) {
+      // With probability 0.5, yield so other threads have a chance to
+      // dispatch events to this queue first.
+      if (ChaosMode::randomUint32LessThan(2)) {
+        PR_Sleep(PR_INTERVAL_NO_WAIT);
+      }
+    }
+
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+    if (!mHead) {
+      mHead = NewPage();
+      if (!mHead) {
+        rv = false;
+      } else {
+        mTail = mHead;
+        mOffsetHead = 0;
+        mOffsetTail = 0;
+      }
+    } else if (mOffsetTail == EVENTS_PER_PAGE) {
+      Page *page = NewPage();
+      if (!page) {
+        rv = false;
+      } else {
+        mTail->mNext = page;
+        mTail = page;
+        mOffsetTail = 0;
+      }
+    }
+    if (rv) {
+      event.swap(mTail->mEvents[mOffsetTail]);
+      ++mOffsetTail;
+      LOG(("EVENTQ(%p): notify\n", this)); 
+      mon.NotifyAll();
+    }
+  }
+  return rv;
+}