diff -r 000000000000 -r 6474c204b198 mfbt/ReentrancyGuard.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/ReentrancyGuard.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,57 @@
+/* -*- 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/. */
+
+/* Small helper class for asserting uses of a class are non-reentrant. */
+
+#ifndef mozilla_ReentrancyGuard_h
+#define mozilla_ReentrancyGuard_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/GuardObjects.h"
+
+namespace mozilla {
+
+/* Useful for implementing containers that assert non-reentrancy */
+class ReentrancyGuard
+{
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+#ifdef DEBUG
+    bool& entered;
+#endif
+
+  public:
+    template<class T>
+#ifdef DEBUG
+    ReentrancyGuard(T& obj
+                    MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : entered(obj.entered)
+#else
+    ReentrancyGuard(T&
+                    MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+#endif
+    {
+      MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+#ifdef DEBUG
+      MOZ_ASSERT(!entered);
+      entered = true;
+#endif
+    }
+    ~ReentrancyGuard()
+    {
+#ifdef DEBUG
+      entered = false;
+#endif
+    }
+
+  private:
+    ReentrancyGuard(const ReentrancyGuard&) MOZ_DELETE;
+    void operator=(const ReentrancyGuard&) MOZ_DELETE;
+};
+
+} // namespace mozilla
+
+#endif /* mozilla_ReentrancyGuard_h */