michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set sw=2 ts=8 et ft=cpp : */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef mozilla_ClearOnShutdown_h
michael@0: #define mozilla_ClearOnShutdown_h
michael@0: 
michael@0: #include "mozilla/LinkedList.h"
michael@0: #include "mozilla/StaticPtr.h"
michael@0: #include "MainThreadUtils.h"
michael@0: 
michael@0: /*
michael@0:  * This header exports one public method in the mozilla namespace:
michael@0:  *
michael@0:  *   template<class SmartPtr>
michael@0:  *   void ClearOnShutdown(SmartPtr *aPtr)
michael@0:  *
michael@0:  * This function takes a pointer to a smart pointer and nulls the smart pointer
michael@0:  * on shutdown.
michael@0:  *
michael@0:  * This is useful if you have a global smart pointer object which you don't
michael@0:  * want to "leak" on shutdown.
michael@0:  *
michael@0:  * Although ClearOnShutdown will work with any smart pointer (i.e., nsCOMPtr,
michael@0:  * nsRefPtr, nsAutoPtr, StaticRefPtr, and StaticAutoPtr), you probably want to
michael@0:  * use it only with StaticRefPtr and StaticAutoPtr.  There is no way to undo a
michael@0:  * call to ClearOnShutdown, so you can call it only on smart pointers which you
michael@0:  * know will live until the program shuts down.  In practice, these are likely
michael@0:  * global variables, which should be Static{Ref,Auto}Ptr.
michael@0:  *
michael@0:  * ClearOnShutdown is currently main-thread only because we don't want to
michael@0:  * accidentally free an object from a different thread than the one it was
michael@0:  * created on.
michael@0:  */
michael@0: 
michael@0: namespace mozilla {
michael@0: namespace ClearOnShutdown_Internal {
michael@0: 
michael@0: class ShutdownObserver : public LinkedListElement<ShutdownObserver>
michael@0: {
michael@0: public:
michael@0:   virtual void Shutdown() = 0;
michael@0:   virtual ~ShutdownObserver() {}
michael@0: };
michael@0: 
michael@0: template<class SmartPtr>
michael@0: class PointerClearer : public ShutdownObserver
michael@0: {
michael@0: public:
michael@0:   PointerClearer(SmartPtr *aPtr)
michael@0:     : mPtr(aPtr)
michael@0:   {}
michael@0: 
michael@0:   virtual void Shutdown()
michael@0:   {
michael@0:     if (mPtr) {
michael@0:       *mPtr = nullptr;
michael@0:     }
michael@0:   }
michael@0: 
michael@0: private:
michael@0:   SmartPtr *mPtr;
michael@0: };
michael@0: 
michael@0: extern bool sHasShutDown;
michael@0: extern StaticAutoPtr<LinkedList<ShutdownObserver> > sShutdownObservers;
michael@0: 
michael@0: } // namespace ClearOnShutdown_Internal
michael@0: 
michael@0: template<class SmartPtr>
michael@0: inline void ClearOnShutdown(SmartPtr *aPtr)
michael@0: {
michael@0:   using namespace ClearOnShutdown_Internal;
michael@0: 
michael@0:   MOZ_ASSERT(NS_IsMainThread());
michael@0:   MOZ_ASSERT(!sHasShutDown);
michael@0: 
michael@0:   if (!sShutdownObservers) {
michael@0:     sShutdownObservers = new LinkedList<ShutdownObserver>();
michael@0:   }
michael@0:   sShutdownObservers->insertBack(new PointerClearer<SmartPtr>(aPtr));
michael@0: }
michael@0: 
michael@0: // Called when XPCOM is shutting down, after all shutdown notifications have
michael@0: // been sent and after all threads' event loops have been purged.
michael@0: inline void KillClearOnShutdown()
michael@0: {
michael@0:   using namespace ClearOnShutdown_Internal;
michael@0: 
michael@0:   MOZ_ASSERT(NS_IsMainThread());
michael@0: 
michael@0:   if (sShutdownObservers) {
michael@0:     ShutdownObserver *observer;
michael@0:     while ((observer = sShutdownObservers->popFirst())) {
michael@0:       observer->Shutdown();
michael@0:       delete observer;
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   sShutdownObservers = nullptr;
michael@0:   sHasShutDown = true;
michael@0: }
michael@0: 
michael@0: } // namespace mozilla
michael@0: 
michael@0: #endif