124 lines
3.8 KiB
C++
124 lines
3.8 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_ClearOnShutdown_h
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#define mozilla_ClearOnShutdown_h
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#include "mozilla/LinkedList.h"
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#include "mozilla/StaticPtr.h"
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#include "mozilla/Array.h"
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#include "MainThreadUtils.h"
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/*
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* This header exports one public method in the mozilla namespace:
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*
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* template<class SmartPtr>
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* void ClearOnShutdown(SmartPtr *aPtr, aPhase=ShutdownPhase::ShutdownFinal)
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*
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* This function takes a pointer to a smart pointer and nulls the smart pointer
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* on shutdown (and a particular phase of shutdown as needed). If a phase
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* is specified, the ptr will be cleared at the start of that phase. Also,
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* if a phase has already occurred when ClearOnShutdown() is called it will
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* cause a MOZ_ASSERT. In case a phase is not explicitly cleared we will
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* clear it on the next phase that occurs.
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*
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* This is useful if you have a global smart pointer object which you don't
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* want to "leak" on shutdown.
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*
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* Although ClearOnShutdown will work with any smart pointer (i.e., nsCOMPtr,
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* nsRefPtr, nsAutoPtr, StaticRefPtr, and StaticAutoPtr), you probably want to
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* use it only with StaticRefPtr and StaticAutoPtr. There is no way to undo a
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* call to ClearOnShutdown, so you can call it only on smart pointers which you
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* know will live until the program shuts down. In practice, these are likely
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* global variables, which should be Static{Ref,Auto}Ptr.
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*
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* ClearOnShutdown is currently main-thread only because we don't want to
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* accidentally free an object from a different thread than the one it was
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* created on.
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*/
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namespace mozilla {
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// Must be contiguous starting at 0
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enum class ShutdownPhase {
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NotInShutdown = 0,
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WillShutdown,
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Shutdown,
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ShutdownThreads,
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ShutdownLoaders,
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ShutdownFinal,
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ShutdownPhase_Length, // never pass this value
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First = WillShutdown, // for iteration
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Last = ShutdownFinal
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};
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namespace ClearOnShutdown_Internal {
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class ShutdownObserver : public LinkedListElement<ShutdownObserver>
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{
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public:
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virtual void Shutdown() = 0;
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virtual ~ShutdownObserver()
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{
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}
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};
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template<class SmartPtr>
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class PointerClearer : public ShutdownObserver
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{
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public:
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explicit PointerClearer(SmartPtr* aPtr)
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: mPtr(aPtr)
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{
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}
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virtual void Shutdown() override
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{
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if (mPtr) {
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*mPtr = nullptr;
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}
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}
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private:
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SmartPtr* mPtr;
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};
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typedef LinkedList<ShutdownObserver> ShutdownList;
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extern Array<StaticAutoPtr<ShutdownList>,
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static_cast<size_t>(ShutdownPhase::ShutdownPhase_Length)> sShutdownObservers;
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extern ShutdownPhase sCurrentShutdownPhase;
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} // namespace ClearOnShutdown_Internal
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template<class SmartPtr>
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inline void
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ClearOnShutdown(SmartPtr* aPtr, ShutdownPhase aPhase = ShutdownPhase::ShutdownFinal)
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{
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using namespace ClearOnShutdown_Internal;
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MOZ_ASSERT(NS_IsMainThread());
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MOZ_ASSERT(aPhase != ShutdownPhase::ShutdownPhase_Length);
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// Adding a ClearOnShutdown for a "past" phase is an error.
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if (!(static_cast<size_t>(sCurrentShutdownPhase) < static_cast<size_t>(aPhase))) {
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MOZ_ASSERT(false, "ClearOnShutdown for phase that already was cleared");
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*aPtr = nullptr;
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return;
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}
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if (!(sShutdownObservers[static_cast<size_t>(aPhase)])) {
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sShutdownObservers[static_cast<size_t>(aPhase)] = new ShutdownList();
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}
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sShutdownObservers[static_cast<size_t>(aPhase)]->insertBack(new PointerClearer<SmartPtr>(aPtr));
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}
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// Called when XPCOM is shutting down, after all shutdown notifications have
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// been sent and after all threads' event loops have been purged.
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void KillClearOnShutdown(ShutdownPhase aPhase);
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} // namespace mozilla
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#endif
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