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diff --git a/xpcom/glue/Mutex.h b/xpcom/glue/Mutex.h
new file mode 100644
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 mozilla_Mutex_h
+#define mozilla_Mutex_h
+
+#include "prlock.h"
+
+#include "mozilla/BlockingResourceBase.h"
+#include "mozilla/GuardObjects.h"
+
+//
+// Provides:
+//
+//  - Mutex, a non-recursive mutex
+//  - MutexAutoLock, an RAII class for ensuring that Mutexes are properly
+//    locked and unlocked
+//  - MutexAutoUnlock, complementary sibling to MutexAutoLock
+//
+//  - OffTheBooksMutex, a non-recursive mutex that doesn't do leak checking
+//  - OffTheBooksMutexAuto{Lock,Unlock} - Like MutexAuto{Lock,Unlock}, but for
+//    an OffTheBooksMutex.
+//
+// Using MutexAutoLock/MutexAutoUnlock etc. is MUCH preferred to making bare
+// calls to Lock and Unlock.
+//
+namespace mozilla {
+
+/**
+ * OffTheBooksMutex is identical to Mutex, except that OffTheBooksMutex doesn't
+ * include leak checking.  Sometimes you want to intentionally "leak" a mutex
+ * until shutdown; in these cases, OffTheBooksMutex is for you.
+ */
+class OffTheBooksMutex : BlockingResourceBase
+{
+public:
+  /**
+   * @param aName A name which can reference this lock
+   * @returns If failure, nullptr
+   *          If success, a valid Mutex* which must be destroyed
+   *          by Mutex::DestroyMutex()
+   **/
+  explicit OffTheBooksMutex(const char* aName)
+    : BlockingResourceBase(aName, eMutex)
+  {
+    mLock = PR_NewLock();
+    if (!mLock) {
+      NS_RUNTIMEABORT("Can't allocate mozilla::Mutex");
+    }
+  }
+
+  ~OffTheBooksMutex()
+  {
+    NS_ASSERTION(mLock,
+                 "improperly constructed Lock or double free");
+    // NSPR does consistency checks for us
+    PR_DestroyLock(mLock);
+    mLock = 0;
+  }
+
+#ifndef DEBUG
+  /**
+   * Lock
+   * @see prlock.h
+   **/
+  void Lock() { PR_Lock(mLock); }
+
+  /**
+   * Unlock
+   * @see prlock.h
+   **/
+  void Unlock() { PR_Unlock(mLock); }
+
+  /**
+   * AssertCurrentThreadOwns
+   * @see prlock.h
+   **/
+  void AssertCurrentThreadOwns() const {}
+
+  /**
+   * AssertNotCurrentThreadOwns
+   * @see prlock.h
+   **/
+  void AssertNotCurrentThreadOwns() const {}
+
+#else
+  void Lock();
+  void Unlock();
+
+  void AssertCurrentThreadOwns() const
+  {
+    PR_ASSERT_CURRENT_THREAD_OWNS_LOCK(mLock);
+  }
+
+  void AssertNotCurrentThreadOwns() const
+  {
+    // FIXME bug 476536
+  }
+
+#endif  // ifndef DEBUG
+
+private:
+  OffTheBooksMutex();
+  OffTheBooksMutex(const OffTheBooksMutex&);
+  OffTheBooksMutex& operator=(const OffTheBooksMutex&);
+
+  PRLock* mLock;
+
+  friend class CondVar;
+
+  // MozPromise needs to access mLock for debugging purpose.
+  template<typename, typename, bool>
+  friend class MozPromise;
+};
+
+/**
+ * Mutex
+ * When possible, use MutexAutoLock/MutexAutoUnlock to lock/unlock this
+ * mutex within a scope, instead of calling Lock/Unlock directly.
+ */
+class Mutex : public OffTheBooksMutex
+{
+public:
+  explicit Mutex(const char* aName)
+    : OffTheBooksMutex(aName)
+  {
+    MOZ_COUNT_CTOR(Mutex);
+  }
+
+  ~Mutex()
+  {
+    MOZ_COUNT_DTOR(Mutex);
+  }
+
+private:
+  Mutex();
+  Mutex(const Mutex&);
+  Mutex& operator=(const Mutex&);
+};
+
+/**
+ * MutexAutoLock
+ * Acquires the Mutex when it enters scope, and releases it when it leaves
+ * scope.
+ *
+ * MUCH PREFERRED to bare calls to Mutex.Lock and Unlock.
+ */
+template<typename T>
+class MOZ_RAII BaseAutoLock
+{
+public:
+  /**
+   * Constructor
+   * The constructor aquires the given lock.  The destructor
+   * releases the lock.
+   *
+   * @param aLock A valid mozilla::Mutex* returned by
+   *              mozilla::Mutex::NewMutex.
+   **/
+  explicit BaseAutoLock(T& aLock MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+    : mLock(&aLock)
+  {
+    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    NS_ASSERTION(mLock, "null mutex");
+    mLock->Lock();
+  }
+
+  ~BaseAutoLock(void)
+  {
+    mLock->Unlock();
+  }
+
+private:
+  BaseAutoLock();
+  BaseAutoLock(BaseAutoLock&);
+  BaseAutoLock& operator=(BaseAutoLock&);
+  static void* operator new(size_t) CPP_THROW_NEW;
+
+  T* mLock;
+  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+typedef BaseAutoLock<Mutex> MutexAutoLock;
+typedef BaseAutoLock<OffTheBooksMutex> OffTheBooksMutexAutoLock;
+
+/**
+ * MutexAutoUnlock
+ * Releases the Mutex when it enters scope, and re-acquires it when it leaves
+ * scope.
+ *
+ * MUCH PREFERRED to bare calls to Mutex.Unlock and Lock.
+ */
+template<typename T>
+class MOZ_RAII BaseAutoUnlock
+{
+public:
+  explicit BaseAutoUnlock(T& aLock MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+    : mLock(&aLock)
+  {
+    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    NS_ASSERTION(mLock, "null lock");
+    mLock->Unlock();
+  }
+
+  ~BaseAutoUnlock()
+  {
+    mLock->Lock();
+  }
+
+private:
+  BaseAutoUnlock();
+  BaseAutoUnlock(BaseAutoUnlock&);
+  BaseAutoUnlock& operator=(BaseAutoUnlock&);
+  static void* operator new(size_t) CPP_THROW_NEW;
+
+  T* mLock;
+  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+typedef BaseAutoUnlock<Mutex> MutexAutoUnlock;
+typedef BaseAutoUnlock<OffTheBooksMutex> OffTheBooksMutexAutoUnlock;
+
+} // namespace mozilla
+
+
+#endif // ifndef mozilla_Mutex_h