mirror of
https://github.com/classilla/tenfourfox.git
synced 2024-09-09 20:54:40 +00:00
177 lines
3.7 KiB
C++
177 lines
3.7 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/. */
|
|
|
|
#ifndef nsTWeakRef_h__
|
|
#define nsTWeakRef_h__
|
|
|
|
#ifndef nsDebug_h___
|
|
#include "nsDebug.h"
|
|
#endif
|
|
|
|
/**
|
|
* A weak reference class for use with generic C++ objects. NOT THREADSAFE!
|
|
*
|
|
* Example usage:
|
|
*
|
|
* class A {
|
|
* public:
|
|
* A() : mWeakSelf(this) {
|
|
* }
|
|
* ~A() {
|
|
* mWeakSelf.forget();
|
|
* }
|
|
* void Bar() { printf("Bar!\n"); }
|
|
* const nsTWeakRef<A> &AsWeakRef() const { return mWeakSelf; }
|
|
* private:
|
|
* nsTWeakRef<A> mWeakSelf;
|
|
* };
|
|
*
|
|
* class B {
|
|
* public:
|
|
* void SetA(const nsTWeakRef<A> &a) {
|
|
* mA = a;
|
|
* }
|
|
* void Foo() {
|
|
* if (mA)
|
|
* mA->Bar();
|
|
* }
|
|
* private:
|
|
* nsTWeakRef<A> mA;
|
|
* };
|
|
*
|
|
* void Test() {
|
|
* B b;
|
|
* {
|
|
* A a;
|
|
* b.SetA(a.AsWeakRef());
|
|
* b.Foo(); // prints "Bar!"
|
|
* }
|
|
* b.Foo(); // prints nothing because |a| has already been destroyed
|
|
* }
|
|
*
|
|
* One can imagine much more complex examples, especially when asynchronous
|
|
* event processing is involved.
|
|
*
|
|
* Keep in mind that you should only ever need a class like this when you have
|
|
* multiple instances of B, such that it is not possible for A and B to simply
|
|
* have pointers to one another.
|
|
*/
|
|
template<class Type>
|
|
class nsTWeakRef
|
|
{
|
|
public:
|
|
~nsTWeakRef()
|
|
{}
|
|
|
|
/**
|
|
* Construct from an object pointer (may be null).
|
|
*/
|
|
explicit nsTWeakRef(Type* aObj = nullptr)
|
|
{
|
|
if (aObj) {
|
|
mRef = new Inner(aObj);
|
|
} else {
|
|
mRef = nullptr;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Construct from another weak reference object.
|
|
*/
|
|
explicit nsTWeakRef(const nsTWeakRef<Type>& aOther) : mRef(aOther.mRef)
|
|
{}
|
|
|
|
/**
|
|
* Assign from an object pointer.
|
|
*/
|
|
nsTWeakRef<Type>& operator=(Type* aObj)
|
|
{
|
|
if (aObj) {
|
|
mRef = new Inner(aObj);
|
|
} else {
|
|
mRef = nullptr;
|
|
}
|
|
return *this;
|
|
}
|
|
|
|
/**
|
|
* Assign from another weak reference object.
|
|
*/
|
|
nsTWeakRef<Type>& operator=(const nsTWeakRef<Type>& aOther)
|
|
{
|
|
mRef = aOther.mRef;
|
|
return *this;
|
|
}
|
|
|
|
/**
|
|
* Get the referenced object. This method may return null if the reference
|
|
* has been cleared or if an out-of-memory error occurred at assignment.
|
|
*/
|
|
Type* get() const { return mRef ? mRef->mObj : nullptr; }
|
|
|
|
/**
|
|
* Called to "null out" the weak reference. Typically, the object referenced
|
|
* by this weak reference calls this method when it is being destroyed.
|
|
* @returns The former referenced object.
|
|
*/
|
|
Type* forget()
|
|
{
|
|
Type* obj;
|
|
if (mRef) {
|
|
obj = mRef->mObj;
|
|
mRef->mObj = nullptr;
|
|
mRef = nullptr;
|
|
} else {
|
|
obj = nullptr;
|
|
}
|
|
return obj;
|
|
}
|
|
|
|
/**
|
|
* Allow |*this| to be treated as a |Type*| for convenience.
|
|
*/
|
|
operator Type*() const { return get(); }
|
|
|
|
/**
|
|
* Allow |*this| to be treated as a |Type*| for convenience. Use with
|
|
* caution since this method will crash if the referenced object is null.
|
|
*/
|
|
Type* operator->() const MOZ_NO_ADDREF_RELEASE_ON_RETURN
|
|
{
|
|
NS_ASSERTION(mRef && mRef->mObj,
|
|
"You can't dereference a null weak reference with operator->().");
|
|
return get();
|
|
}
|
|
|
|
private:
|
|
|
|
struct Inner
|
|
{
|
|
int mCnt;
|
|
Type* mObj;
|
|
|
|
explicit Inner(Type* aObj)
|
|
: mCnt(1)
|
|
, mObj(aObj)
|
|
{
|
|
}
|
|
void AddRef()
|
|
{
|
|
++mCnt;
|
|
}
|
|
void Release()
|
|
{
|
|
if (--mCnt == 0) {
|
|
delete this;
|
|
}
|
|
}
|
|
};
|
|
|
|
RefPtr<Inner> mRef;
|
|
};
|
|
|
|
#endif // nsTWeakRef_h__
|