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/* -*- 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_ClearOnShutdown_h
#define mozilla_ClearOnShutdown_h
#include "mozilla/LinkedList.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/Array.h"
#include "MainThreadUtils.h"
/*
* This header exports one public method in the mozilla namespace:
*
* template<class SmartPtr>
* void ClearOnShutdown(SmartPtr *aPtr, aPhase=ShutdownPhase::ShutdownFinal)
*
* This function takes a pointer to a smart pointer and nulls the smart pointer
* on shutdown (and a particular phase of shutdown as needed). If a phase
* is specified, the ptr will be cleared at the start of that phase. Also,
* if a phase has already occurred when ClearOnShutdown() is called it will
* cause a MOZ_ASSERT. In case a phase is not explicitly cleared we will
* clear it on the next phase that occurs.
*
* 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 {
// Must be contiguous starting at 0
enum class ShutdownPhase {
NotInShutdown = 0,
WillShutdown,
Shutdown,
ShutdownThreads,
ShutdownLoaders,
ShutdownFinal,
ShutdownPhase_Length, // never pass this value
First = WillShutdown, // for iteration
Last = ShutdownFinal
};
namespace ClearOnShutdown_Internal {
class ShutdownObserver : public LinkedListElement<ShutdownObserver>
{
public:
virtual void Shutdown() = 0;
virtual ~ShutdownObserver()
{
}
};
template<class SmartPtr>
class PointerClearer : public ShutdownObserver
{
public:
explicit PointerClearer(SmartPtr* aPtr)
: mPtr(aPtr)
{
}
virtual void Shutdown() override
{
if (mPtr) {
*mPtr = nullptr;
}
}
private:
SmartPtr* mPtr;
};
typedef LinkedList<ShutdownObserver> ShutdownList;
extern Array<StaticAutoPtr<ShutdownList>,
static_cast<size_t>(ShutdownPhase::ShutdownPhase_Length)> sShutdownObservers;
extern ShutdownPhase sCurrentShutdownPhase;
} // namespace ClearOnShutdown_Internal
template<class SmartPtr>
inline void
ClearOnShutdown(SmartPtr* aPtr, ShutdownPhase aPhase = ShutdownPhase::ShutdownFinal)
{
using namespace ClearOnShutdown_Internal;
MOZ_ASSERT(NS_IsMainThread());
MOZ_ASSERT(aPhase != ShutdownPhase::ShutdownPhase_Length);
// Adding a ClearOnShutdown for a "past" phase is an error.
if (!(static_cast<size_t>(sCurrentShutdownPhase) < static_cast<size_t>(aPhase))) {
MOZ_ASSERT(false, "ClearOnShutdown for phase that already was cleared");
*aPtr = nullptr;
return;
}
if (!(sShutdownObservers[static_cast<size_t>(aPhase)])) {
sShutdownObservers[static_cast<size_t>(aPhase)] = new ShutdownList();
}
sShutdownObservers[static_cast<size_t>(aPhase)]->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.
void KillClearOnShutdown(ShutdownPhase aPhase);
} // namespace mozilla
#endif
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