From 912f11f92b3e18e110d3e63d2a37a1fa90daa15e Mon Sep 17 00:00:00 2001
From: Andrew McCreight <continuation@gmail.com>
Date: Tue, 21 Jul 2015 11:31:44 -0700
Subject: [PATCH] Bug 1179924 - Create a more modern JS object holder for
 cross-thread references to JS objects. r=smaug

---
 xpcom/base/JSObjectHolder.cpp |  9 ++++++++
 xpcom/base/JSObjectHolder.h   | 42 +++++++++++++++++++++++++++++++++++
 xpcom/base/moz.build          |  2 ++
 3 files changed, 53 insertions(+)
 create mode 100644 xpcom/base/JSObjectHolder.cpp
 create mode 100644 xpcom/base/JSObjectHolder.h

diff --git a/xpcom/base/JSObjectHolder.cpp b/xpcom/base/JSObjectHolder.cpp
new file mode 100644
index 00000000000..5bcc3cabbf4
--- /dev/null
+++ b/xpcom/base/JSObjectHolder.cpp
@@ -0,0 +1,9 @@
+/* -*- 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/. */
+
+#include "JSObjectHolder.h"
+
+NS_IMPL_ISUPPORTS(mozilla::JSObjectHolder, nsISupports)
diff --git a/xpcom/base/JSObjectHolder.h b/xpcom/base/JSObjectHolder.h
new file mode 100644
index 00000000000..7b83b813db2
--- /dev/null
+++ b/xpcom/base/JSObjectHolder.h
@@ -0,0 +1,42 @@
+/* -*- 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_JSObjectHolder_h
+#define mozilla_JSObjectHolder_h
+
+#include "js/RootingAPI.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla {
+
+// This class is useful when something on one thread needs to keep alive
+// a JS Object from another thread. If they are both on the same thread, the
+// owning class should instead be made a cycle collected SCRIPT_HOLDER class.
+// This object should only be AddRefed and Released on the same thread as
+// mJSObject.
+//
+// Note that this keeps alive the JS object until it goes away, so be sure not to
+// create cycles that keep alive the holder.
+//
+// JSObjectHolder is ISupports to make it usable with NS_ReleaseOnMainThread.
+class JSObjectHolder final : public nsISupports
+{
+public:
+  JSObjectHolder(JSContext* aCx, JSObject* aObject) : mJSObject(aCx, aObject) {}
+
+  NS_DECL_ISUPPORTS
+
+  JSObject* GetJSObject() { return mJSObject; }
+
+private:
+  ~JSObjectHolder() {}
+
+  JS::PersistentRooted<JSObject*> mJSObject;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_JSObjectHolder_h
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
index c9ddd3f42fd..bb2f2619a3e 100644
--- a/xpcom/base/moz.build
+++ b/xpcom/base/moz.build
@@ -75,6 +75,7 @@ EXPORTS.mozilla += [
     'DeferredFinalize.h',
     'ErrorNames.h',
     'HoldDropJSObjects.h',
+    'JSObjectHolder.h',
     'LinuxUtils.h',
     'nsMemoryInfoDumper.h',
     'StaticMutex.h',
@@ -98,6 +99,7 @@ UNIFIED_SOURCES += [
     'DeferredFinalize.cpp',
     'ErrorNames.cpp',
     'HoldDropJSObjects.cpp',
+    'JSObjectHolder.cpp',
     'nsConsoleMessage.cpp',
     'nsConsoleService.cpp',
     'nsCycleCollector.cpp',