gecko-dev/xpcom/base/ClearOnShutdown.h

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2.9 KiB
C++

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