diff -r 000000000000 -r 6474c204b198 content/media/SharedThreadPool.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/content/media/SharedThreadPool.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,90 @@
+/* -*- 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 SharedThreadPool_h_
+#define SharedThreadPool_h_
+
+#include <queue>
+#include "mozilla/RefPtr.h"
+#include "nsThreadUtils.h"
+#include "nsIThreadPool.h"
+#include "nsISupports.h"
+#include "nsISupportsImpl.h"
+#include "nsCOMPtr.h"
+
+namespace mozilla {
+
+// Wrapper that makes an nsIThreadPool a singleton, and provides a
+// consistent threadsafe interface to get instances. Callers simply get a
+// SharedThreadPool by the name of its nsIThreadPool. All get requests of
+// the same name get the same SharedThreadPool. Users must store a reference
+// to the pool, and when the last reference to a SharedThreadPool is dropped
+// the pool is shutdown and deleted. Users aren't required to manually
+// shutdown the pool, and can release references on any thread. On Windows
+// all threads in the pool have MSCOM initialized with COINIT_MULTITHREADED.
+class SharedThreadPool : public nsIThreadPool
+{
+public:
+
+  // Gets (possibly creating) the shared thread pool singleton instance with
+  // thread pool named aName.
+  // *Must* be called on the main thread.
+  static TemporaryRef<SharedThreadPool> Get(const nsCString& aName,
+                                            uint32_t aThreadLimit = 4);
+
+  // Spins the event loop until all thread pools are shutdown.
+  // *Must* be called on the main thread.
+  static void SpinUntilShutdown();
+
+  // We implement custom threadsafe AddRef/Release pair, that destroys the
+  // the shared pool singleton when the refcount drops to 0. The addref/release
+  // are implemented using locking, so it's not recommended that you use them
+  // in a tight loop.
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr);
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(MozExternalRefCountType) Release(void);
+
+  // Forward behaviour to wrapped thread pool implementation.
+  NS_FORWARD_SAFE_NSITHREADPOOL(mPool);
+  NS_FORWARD_SAFE_NSIEVENTTARGET(GetEventTarget());
+
+  nsIEventTarget* GetEventTarget() {
+    return mEventTarget;
+  }
+
+private:
+
+  // Creates necessary statics.
+  // Main thread only.
+  static void EnsureInitialized();
+
+  // Creates a singleton SharedThreadPool wrapper around aPool.
+  // aName is the name of the aPool, and is used to lookup the
+  // SharedThreadPool in the hash table of all created pools.
+  SharedThreadPool(const nsCString& aName,
+                   nsIThreadPool* aPool);
+  virtual ~SharedThreadPool();
+
+  nsresult EnsureThreadLimitIsAtLeast(uint32_t aThreadLimit);
+
+  // Name of mPool.
+  const nsCString mName;
+
+  // Thread pool being wrapped.
+  nsCOMPtr<nsIThreadPool> mPool;
+
+  // Refcount. We implement custom ref counting so that the thread pool is
+  // shutdown in a threadsafe manner and singletonness is preserved.
+  nsrefcnt mRefCnt;
+
+  // mPool QI'd to nsIEventTarget. We cache this, so that we can use
+  // NS_FORWARD_SAFE_NSIEVENTTARGET above.
+  nsCOMPtr<nsIEventTarget> mEventTarget;
+};
+
+} // namespace mozilla
+
+#endif // SharedThreadPool_h_