Bug 1186745 part 1 - Add LeakRefPtr for pointer leaking by default. r=froydnj

This class can be used instead of raw pointer for a sound leaking-by-default
behavior. Also it could take advantage of move semantic check in the future.

--HG--
extra : source : 6bf72b4eaa92b13d42b547d8aeee677489a4d3e2

xpcom/glue/moz.build

@@ -106,6 +106,7 @@ if CONFIG['_MSC_VER']:
 
 LOCAL_INCLUDES += [
     '../build',
+    '../threads',
 ]
 
 if CONFIG['ENABLE_TESTS']:

xpcom/glue/nsThreadUtils.cpp

@@ -7,6 +7,7 @@
 #include "nsThreadUtils.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/Likely.h"
+#include "LeakRefPtr.h"
 
 #ifdef MOZILLA_INTERNAL_API
 # include "nsThreadManager.h"
@@ -27,6 +28,8 @@ using mozilla::IsVistaOrLater;
 #include <pratom.h>
 #include <prthread.h>
 
+using namespace mozilla;
+
 #ifndef XPCOM_GLUE_AVOID_NSPR
 
 NS_IMPL_ISUPPORTS(nsRunnable, nsIRunnable)
@@ -164,17 +167,16 @@ NS_DispatchToCurrentThread(nsIRunnable* aEvent)
 NS_METHOD
 NS_DispatchToMainThread(already_AddRefed<nsIRunnable>&& aEvent, uint32_t aDispatchFlags)
 {
-  nsCOMPtr<nsIRunnable> event(aEvent);
+  LeakRefPtr<nsIRunnable> event(Move(aEvent));
   nsCOMPtr<nsIThread> thread;
   nsresult rv = NS_GetMainThread(getter_AddRefs(thread));
   if (NS_WARN_IF(NS_FAILED(rv))) {
     NS_ASSERTION(false, "Failed NS_DispatchToMainThread() in shutdown; leaking");
     // NOTE: if you stop leaking here, adjust Promise::MaybeReportRejected(),
     // which assumes a leak here, or split into leaks and no-leaks versions
-    nsIRunnable* temp = event.forget().take(); // leak without using "unused <<" due to Windows (boo)
-    return temp ? rv : rv; // to make compiler not bletch on us
+    return rv;
   }
-  return thread->Dispatch(event.forget(), aDispatchFlags);
+  return thread->Dispatch(event.take(), aDispatchFlags);
 }
 
 // In the case of failure with a newly allocated runnable with a

xpcom/glue/standalone/moz.build

@@ -38,6 +38,7 @@ DEFINES['XPCOM_GLUE'] = True
 
 LOCAL_INCLUDES += [
     '../../build',
+    '../../threads',
 ]
 
 # Don't use STL wrappers here (i.e. wrapped <new>); they require mozalloc

xpcom/glue/standalone/staticruntime/moz.build

@@ -30,6 +30,7 @@ DEFINES['XPCOM_GLUE'] = True
 
 LOCAL_INCLUDES += [
     '../../../build',
+    '../../../threads',
 ]
 
 # Statically link to the CRT on Windows

xpcom/glue/staticruntime/moz.build

@@ -28,6 +28,7 @@ if CONFIG['_MSC_VER']:
 
 LOCAL_INCLUDES += [
     '../../build',
+    '../../threads',
 ]
 
 # Statically link to the CRT on Windows

xpcom/threads/LeakRefPtr.h

@@ -0,0 +1,52 @@
+/* -*- 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/. */
+
+/* Smart pointer which leaks its owning refcounted object by default. */
+
+#ifndef LeakRefPtr_h
+#define LeakRefPtr_h
+
+#include "mozilla/AlreadyAddRefed.h"
+
+namespace mozilla {
+
+/**
+ * Instance of this class behaves like a raw pointer which leaks the
+ * resource it's owning if not explicitly released.
+ */
+template<class T>
+class LeakRefPtr
+{
+public:
+  explicit LeakRefPtr(already_AddRefed<T>&& aPtr)
+    : mRawPtr(aPtr.take()) { }
+
+  explicit operator bool() const { return !!mRawPtr; }
+
+  LeakRefPtr<T>& operator=(already_AddRefed<T>&& aPtr)
+  {
+    mRawPtr = aPtr.take();
+    return *this;
+  }
+
+  T* get() const { return mRawPtr; }
+
+  already_AddRefed<T> take()
+  {
+    T* rawPtr = mRawPtr;
+    mRawPtr = nullptr;
+    return already_AddRefed<T>(rawPtr);
+  }
+
+  void release() { NS_RELEASE(mRawPtr); }
+
+private:
+  T* MOZ_OWNING_REF mRawPtr;
+};
+
+} // namespace mozilla
+
+#endif // LeakRefPtr_h

xpcom/threads/nsThread.cpp

@@ -36,6 +36,7 @@
 #include "nsXPCOMPrivate.h"
 #include "mozilla/ChaosMode.h"
 #include "mozilla/TimeStamp.h"
+#include "LeakRefPtr.h"
 
 #ifdef MOZ_CRASHREPORTER
 #include "nsServiceManagerUtils.h"
@@ -541,6 +542,9 @@ nsThread::PutEvent(nsIRunnable* aEvent, nsNestedEventTarget* aTarget)
 nsresult
 nsThread::PutEvent(already_AddRefed<nsIRunnable>&& aEvent, nsNestedEventTarget* aTarget)
 {
+  // We want to leak the reference when we fail to dispatch it, so that
+  // we won't release the event in a wrong thread.
+  LeakRefPtr<nsIRunnable> event(Move(aEvent));
   nsCOMPtr<nsIThreadObserver> obs;
 
 #ifdef MOZ_NUWA_PROCESS
@@ -554,11 +558,9 @@ nsThread::PutEvent(already_AddRefed<nsIRunnable>&& aEvent, nsNestedEventTarget*
     nsChainedEventQueue* queue = aTarget ? aTarget->mQueue : &mEventsRoot;
     if (!queue || (queue == &mEventsRoot && mEventsAreDoomed)) {
       NS_WARNING("An event was posted to a thread that will never run it (rejected)");
-      nsCOMPtr<nsIRunnable> temp(aEvent);
-      nsIRunnable* temp2 = temp.forget().take(); // can't use unused << aEvent here due to Windows (boo)
-      return temp2 ? NS_ERROR_UNEXPECTED : NS_ERROR_UNEXPECTED; // to make compiler not bletch on us
+      return NS_ERROR_UNEXPECTED;
     }
-    queue->PutEvent(Move(aEvent), lock);
+    queue->PutEvent(event.take(), lock);
 
     // Make sure to grab the observer before dropping the lock, otherwise the
     // event that we just placed into the queue could run and eventually delete