mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-27 23:02:20 +00:00
1b9b84bbce
This allows for nice template type deducation. Differential Revision: https://phabricator.services.mozilla.com/D96368
359 lines
12 KiB
C++
359 lines
12 KiB
C++
/* -*- 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/. */
|
|
|
|
/* Weak pointer functionality, implemented as a mixin for use with any class. */
|
|
|
|
/**
|
|
* SupportsWeakPtr lets you have a pointer to an object 'Foo' without affecting
|
|
* its lifetime. It works by creating a single shared reference counted object
|
|
* (WeakReference) that each WeakPtr will access 'Foo' through. This lets 'Foo'
|
|
* clear the pointer in the WeakReference without having to know about all of
|
|
* the WeakPtrs to it and allows the WeakReference to live beyond the lifetime
|
|
* of 'Foo'.
|
|
*
|
|
* PLEASE NOTE: This weak pointer implementation is not thread-safe.
|
|
*
|
|
* The overhead of WeakPtr is that accesses to 'Foo' becomes an additional
|
|
* dereference, and an additional heap allocated pointer sized object shared
|
|
* between all of the WeakPtrs.
|
|
*
|
|
* Example of usage:
|
|
*
|
|
* // To have a class C support weak pointers, inherit from
|
|
* // SupportsWeakPtr
|
|
* class C : public SupportsWeakPtr
|
|
* {
|
|
* public:
|
|
* int mNum;
|
|
* void act();
|
|
* };
|
|
*
|
|
* C* ptr = new C();
|
|
*
|
|
* // Get weak pointers to ptr. The first time a weak pointer
|
|
* // is obtained, a reference counted WeakReference object is created that
|
|
* // can live beyond the lifetime of 'ptr'. The WeakReference
|
|
* // object will be notified of 'ptr's destruction.
|
|
* WeakPtr<C> weak = ptr;
|
|
* WeakPtr<C> other = ptr;
|
|
*
|
|
* // Test a weak pointer for validity before using it.
|
|
* if (weak) {
|
|
* weak->mNum = 17;
|
|
* weak->act();
|
|
* }
|
|
*
|
|
* // Destroying the underlying object clears weak pointers to it.
|
|
* delete ptr;
|
|
*
|
|
* MOZ_ASSERT(!weak, "Deleting |ptr| clears weak pointers to it.");
|
|
* MOZ_ASSERT(!other, "Deleting |ptr| clears all weak pointers to it.");
|
|
*
|
|
* WeakPtr is typesafe and may be used with any class. It is not required that
|
|
* the class be reference-counted or allocated in any particular way.
|
|
*
|
|
* The API was loosely inspired by Chromium's weak_ptr.h:
|
|
* http://src.chromium.org/svn/trunk/src/base/memory/weak_ptr.h
|
|
*
|
|
* Note that multiple base classes inheriting from SupportsWeakPtr is not
|
|
* currently supported. We could support it if needed though.
|
|
*
|
|
* For Gecko-internal usage there is also MainThreadWeakPtr<T>, a version of
|
|
* WeakPtr that can be destroyed on any thread, but whose release gets proxied
|
|
* to the main thread. This is a similar API to nsMainThreadPtrHandle, but
|
|
* without keeping a strong reference to the main-thread object. Said WeakPtr
|
|
* can't be accessed from any other thread that isn't the main thread.
|
|
*/
|
|
|
|
#ifndef mozilla_WeakPtr_h
|
|
#define mozilla_WeakPtr_h
|
|
|
|
#include "mozilla/ArrayUtils.h"
|
|
#include "mozilla/Assertions.h"
|
|
#include "mozilla/Attributes.h"
|
|
#include "mozilla/Maybe.h"
|
|
#include "mozilla/RefCounted.h"
|
|
#include "mozilla/RefPtr.h"
|
|
|
|
#include <string.h>
|
|
#include <type_traits>
|
|
|
|
#if defined(MOZILLA_INTERNAL_API)
|
|
// For thread safety checking.
|
|
# include "nsISupportsImpl.h"
|
|
// For main thread destructor behavior.
|
|
# include "nsProxyRelease.h"
|
|
#endif
|
|
|
|
#if defined(MOZILLA_INTERNAL_API) && \
|
|
defined(MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED)
|
|
|
|
// Weak referencing is not implemented as thread safe. When a WeakPtr
|
|
// is created or dereferenced on thread A but the real object is just
|
|
// being Released() on thread B, there is a possibility of a race
|
|
// when the proxy object (detail::WeakReference) is notified about
|
|
// the real object destruction just between when thread A is storing
|
|
// the object pointer locally and is about to add a reference to it.
|
|
//
|
|
// Hence, a non-null weak proxy object is considered to have a single
|
|
// "owning thread". It means that each query for a weak reference,
|
|
// its dereference, and destruction of the real object must all happen
|
|
// on a single thread. The following macros implement assertions for
|
|
// checking these conditions.
|
|
//
|
|
// We re-use XPCOM's nsAutoOwningEventTarget checks when they are available.
|
|
// This has the advantage that it works with cooperative thread pools.
|
|
|
|
# define MOZ_WEAKPTR_DECLARE_THREAD_SAFETY_CHECK \
|
|
/* Will be none if mPtr = nullptr. */ \
|
|
Maybe<nsAutoOwningEventTarget> _owningThread;
|
|
# define MOZ_WEAKPTR_INIT_THREAD_SAFETY_CHECK() \
|
|
do { \
|
|
if (p) { \
|
|
_owningThread.emplace(); \
|
|
} \
|
|
} while (false)
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY() \
|
|
do { \
|
|
MOZ_DIAGNOSTIC_ASSERT( \
|
|
!_owningThread || _owningThread->IsCurrentThread(), \
|
|
"WeakPtr accessed from multiple threads"); \
|
|
} while (false)
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED(that) \
|
|
(that)->AssertThreadSafety();
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED_IF(that) \
|
|
do { \
|
|
if (that) { \
|
|
(that)->AssertThreadSafety(); \
|
|
} \
|
|
} while (false)
|
|
|
|
# define MOZ_WEAKPTR_THREAD_SAFETY_CHECKING 1
|
|
|
|
#else
|
|
|
|
# define MOZ_WEAKPTR_DECLARE_THREAD_SAFETY_CHECK
|
|
# define MOZ_WEAKPTR_INIT_THREAD_SAFETY_CHECK() \
|
|
do { \
|
|
} while (false)
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY() \
|
|
do { \
|
|
} while (false)
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED(that) \
|
|
do { \
|
|
} while (false)
|
|
# define MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED_IF(that) \
|
|
do { \
|
|
} while (false)
|
|
|
|
#endif
|
|
|
|
namespace mozilla {
|
|
|
|
namespace detail {
|
|
|
|
enum class WeakPtrDestructorBehavior {
|
|
Normal,
|
|
#ifdef MOZILLA_INTERNAL_API
|
|
ProxyToMainThread,
|
|
#endif
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
template <typename T, detail::WeakPtrDestructorBehavior =
|
|
detail::WeakPtrDestructorBehavior::Normal>
|
|
class WeakPtr;
|
|
class SupportsWeakPtr;
|
|
|
|
namespace detail {
|
|
|
|
// This can live beyond the lifetime of the class derived from
|
|
// SupportsWeakPtr.
|
|
class WeakReference : public ::mozilla::RefCounted<WeakReference> {
|
|
public:
|
|
explicit WeakReference(const SupportsWeakPtr* p)
|
|
: mPtr(const_cast<SupportsWeakPtr*>(p)) {
|
|
MOZ_WEAKPTR_INIT_THREAD_SAFETY_CHECK();
|
|
}
|
|
|
|
SupportsWeakPtr* get() const {
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY();
|
|
return mPtr;
|
|
}
|
|
|
|
#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
|
|
const char* typeName() const { return "WeakReference"; }
|
|
size_t typeSize() const { return sizeof(*this); }
|
|
#endif
|
|
|
|
#ifdef MOZ_WEAKPTR_THREAD_SAFETY_CHECKING
|
|
void AssertThreadSafety() { MOZ_WEAKPTR_ASSERT_THREAD_SAFETY(); }
|
|
#endif
|
|
|
|
private:
|
|
friend class mozilla::SupportsWeakPtr;
|
|
|
|
void detach() {
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY();
|
|
mPtr = nullptr;
|
|
}
|
|
|
|
SupportsWeakPtr* MOZ_NON_OWNING_REF mPtr;
|
|
MOZ_WEAKPTR_DECLARE_THREAD_SAFETY_CHECK
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
class SupportsWeakPtr {
|
|
using WeakReference = detail::WeakReference;
|
|
|
|
protected:
|
|
~SupportsWeakPtr() { DetachWeakPtr(); }
|
|
|
|
protected:
|
|
void DetachWeakPtr() {
|
|
if (mSelfReferencingWeakReference) {
|
|
mSelfReferencingWeakReference->detach();
|
|
}
|
|
}
|
|
|
|
private:
|
|
WeakReference* SelfReferencingWeakReference() const {
|
|
if (!mSelfReferencingWeakReference) {
|
|
mSelfReferencingWeakReference = new WeakReference(this);
|
|
} else {
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED(mSelfReferencingWeakReference);
|
|
}
|
|
return mSelfReferencingWeakReference.get();
|
|
}
|
|
|
|
template <typename U, detail::WeakPtrDestructorBehavior>
|
|
friend class WeakPtr;
|
|
|
|
mutable RefPtr<WeakReference> mSelfReferencingWeakReference;
|
|
};
|
|
|
|
template <typename T, detail::WeakPtrDestructorBehavior Destruct>
|
|
class WeakPtr {
|
|
using WeakReference = detail::WeakReference;
|
|
|
|
public:
|
|
WeakPtr& operator=(const WeakPtr& aOther) {
|
|
// We must make sure the reference we have now is safe to be dereferenced
|
|
// before we throw it away... (this can be called from a ctor)
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED_IF(mRef);
|
|
// ...and make sure the new reference is used on a single thread as well.
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED(aOther.mRef);
|
|
|
|
mRef = aOther.mRef;
|
|
return *this;
|
|
}
|
|
|
|
WeakPtr(const WeakPtr& aOther) {
|
|
// The thread safety check is performed inside of the operator= method.
|
|
*this = aOther;
|
|
}
|
|
|
|
WeakPtr& operator=(decltype(nullptr)) {
|
|
// We must make sure the reference we have now is safe to be dereferenced
|
|
// before we throw it away.
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED_IF(mRef);
|
|
if (!mRef || mRef->get()) {
|
|
// Ensure that mRef is dereferenceable in the uninitialized state.
|
|
mRef = new WeakReference(nullptr);
|
|
}
|
|
return *this;
|
|
}
|
|
|
|
WeakPtr& operator=(const T* aOther) {
|
|
// We must make sure the reference we have now is safe to be dereferenced
|
|
// before we throw it away.
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED_IF(mRef);
|
|
if (aOther) {
|
|
mRef = aOther->SelfReferencingWeakReference();
|
|
} else if (!mRef || mRef->get()) {
|
|
// Ensure that mRef is dereferenceable in the uninitialized state.
|
|
mRef = new WeakReference(nullptr);
|
|
}
|
|
// The thread safety check happens inside SelfReferencingWeakPtr
|
|
// or is initialized in the WeakReference constructor.
|
|
return *this;
|
|
}
|
|
|
|
MOZ_IMPLICIT WeakPtr(T* aOther) {
|
|
*this = aOther;
|
|
#ifdef MOZILLA_INTERNAL_API
|
|
if (Destruct == detail::WeakPtrDestructorBehavior::ProxyToMainThread) {
|
|
MOZ_ASSERT(NS_IsMainThread(),
|
|
"MainThreadWeakPtr makes no sense on non-main threads");
|
|
}
|
|
#endif
|
|
}
|
|
|
|
explicit WeakPtr(const RefPtr<T>& aOther) : WeakPtr(aOther.get()) {}
|
|
|
|
// Ensure that mRef is dereferenceable in the uninitialized state.
|
|
WeakPtr() : mRef(new WeakReference(nullptr)) {}
|
|
|
|
explicit operator bool() const { return mRef->get(); }
|
|
T* get() const { return static_cast<T*>(mRef->get()); }
|
|
operator T*() const { return get(); }
|
|
T& operator*() const { return *get(); }
|
|
T* operator->() const MOZ_NO_ADDREF_RELEASE_ON_RETURN { return get(); }
|
|
|
|
#ifdef MOZILLA_INTERNAL_API
|
|
~WeakPtr() {
|
|
if (Destruct == detail::WeakPtrDestructorBehavior::ProxyToMainThread) {
|
|
NS_ReleaseOnMainThread("WeakPtr::mRef", mRef.forget());
|
|
} else {
|
|
MOZ_WEAKPTR_ASSERT_THREAD_SAFETY_DELEGATED(mRef);
|
|
}
|
|
}
|
|
#endif
|
|
|
|
private:
|
|
friend class SupportsWeakPtr;
|
|
|
|
explicit WeakPtr(const RefPtr<WeakReference>& aOther) : mRef(aOther) {}
|
|
|
|
RefPtr<WeakReference> mRef;
|
|
};
|
|
|
|
#ifdef MOZILLA_INTERNAL_API
|
|
|
|
template <typename T>
|
|
using MainThreadWeakPtr =
|
|
WeakPtr<T, detail::WeakPtrDestructorBehavior::ProxyToMainThread>;
|
|
|
|
#endif
|
|
|
|
#define NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR tmp->DetachWeakPtr();
|
|
|
|
#define NS_IMPL_CYCLE_COLLECTION_WEAK_PTR(class_, ...) \
|
|
NS_IMPL_CYCLE_COLLECTION_CLASS(class_) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_) \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
|
|
|
|
#define NS_IMPL_CYCLE_COLLECTION_WEAK_PTR_INHERITED(class_, super_, ...) \
|
|
NS_IMPL_CYCLE_COLLECTION_CLASS(class_) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(class_, super_) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR \
|
|
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(class_, super_) \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
|
|
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif /* mozilla_WeakPtr_h */
|