diff -r 000000000000 -r 6474c204b198 xpcom/threads/nsEventQueue.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/threads/nsEventQueue.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,92 @@
+/* -*- 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/. */
+
+#ifndef nsEventQueue_h__
+#define nsEventQueue_h__
+
+#include <stdlib.h>
+#include "mozilla/ReentrantMonitor.h"
+#include "nsIRunnable.h"
+
+// A threadsafe FIFO event queue...
+class nsEventQueue
+{
+  typedef mozilla::ReentrantMonitor ReentrantMonitor;
+
+public:
+  nsEventQueue();
+  ~nsEventQueue();
+
+  // This method adds a new event to the pending event queue.  The event object
+  // is AddRef'd if this method succeeds.  This method returns true if the
+  // event was stored in the event queue, and it returns false if it could
+  // not allocate sufficient memory.
+  bool PutEvent(nsIRunnable *event);
+
+  // This method gets an event from the event queue.  If mayWait is true, then
+  // the method will block the calling thread until an event is available.  If
+  // the event is null, then the method returns immediately indicating whether
+  // or not an event is pending.  When the resulting event is non-null, the
+  // caller is responsible for releasing the event object.  This method does
+  // not alter the reference count of the resulting event.
+  bool GetEvent(bool mayWait, nsIRunnable **event);
+
+  // This method returns true if there is a pending event.
+  bool HasPendingEvent() {
+    return GetEvent(false, nullptr);
+  }
+
+  // This method returns the next pending event or null.
+  bool GetPendingEvent(nsIRunnable **runnable) {
+    return GetEvent(false, runnable);
+  }
+
+  // This method waits for and returns the next pending event.
+  bool WaitPendingEvent(nsIRunnable **runnable) {
+    return GetEvent(true, runnable);
+  }
+
+  // Expose the event queue's monitor for "power users"
+  ReentrantMonitor& GetReentrantMonitor() {
+    return mReentrantMonitor;
+  }
+
+private:
+
+  bool IsEmpty() {
+    return !mHead || (mHead == mTail && mOffsetHead == mOffsetTail);
+  }
+
+  enum { EVENTS_PER_PAGE = 255 };
+
+  // Page objects are linked together to form a simple deque.
+
+  struct Page {
+    struct Page *mNext;
+    nsIRunnable *mEvents[EVENTS_PER_PAGE];
+  };
+
+  static_assert((sizeof(Page) & (sizeof(Page) - 1)) == 0,
+                "sizeof(Page) should be a power of two to avoid heap slop.");
+
+  static Page *NewPage() {
+    return static_cast<Page *>(calloc(1, sizeof(Page)));
+  }
+
+  static void FreePage(Page *p) {
+    free(p);
+  }
+
+  ReentrantMonitor mReentrantMonitor;
+
+  Page *mHead;
+  Page *mTail;
+
+  uint16_t mOffsetHead;  // offset into mHead where next item is removed
+  uint16_t mOffsetTail;  // offset into mTail where next item is added
+};
+
+#endif  // nsEventQueue_h__