RefPtr.h
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at:
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Code.
*
* The Initial Developer of the Original Code is
* The Mozilla Foundation
* Portions created by the Initial Developer are Copyright (C) 2011
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Chris Jones <jones.chris.g@gmail.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
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* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef mozilla_RefPtr_h_
#define mozilla_RefPtr_h_
#include "mozilla/Util.h"
/**
* Helpers for defining and using refcounted objects.
*/
namespace mozilla {
template<typename T> class RefCounted;
template<typename T> class RefPtr;
template<typename T> class TemporaryRef;
template<typename T> class OutParamRef;
template<typename T> OutParamRef<T> byRef(RefPtr<T>&);
/**
* RefCounted<T> is a sort of a "mixin" for a class T. RefCounted
* manages, well, refcounting for T, and because RefCounted is
* parameterized on T, RefCounted<T> can call T's destructor directly.
* This means T doesn't need to have a virtual dtor and so doesn't
* need a vtable.
*
* RefCounted<T> is created with refcount == 0. Newly-allocated
* RefCounted<T> must immediately be assigned to a RefPtr to make the
* refcount > 0. It's an error to allocate and free a bare
* RefCounted<T>, i.e. outside of the RefPtr machinery. Attempts to
* do so will abort DEBUG builds.
*
* Live RefCounted<T> have refcount > 0. The lifetime (refcounts) of
* live RefCounted<T> are controlled by RefPtr<T> and
* RefPtr<super/subclass of T>. Upon a transition from refcounted==1
* to 0, the RefCounted<T> "dies" and is destroyed. The "destroyed"
* state is represented in DEBUG builds by refcount==-0xdead. This
* state distinguishes use-before-ref (refcount==0) from
* use-after-destroy (refcount==-0xdead).
*/
template<typename T>
class RefCounted
{
friend class RefPtr<T>;
public:
RefCounted() : refCnt(0) { }
~RefCounted() { MOZ_ASSERT(refCnt == -0xdead); }
// Compatibility with nsRefPtr.
void AddRef() {
MOZ_ASSERT(refCnt >= 0);
++refCnt;
}
void Release() {
MOZ_ASSERT(refCnt > 0);
if (0 == --refCnt) {
#ifdef DEBUG
refCnt = -0xdead;
#endif
delete static_cast<T*>(this);
}
}
// Compatibility with wtf::RefPtr.
void ref() { AddRef(); }
void deref() { Release(); }
int refCount() const { return refCnt; }
bool hasOneRef() const {
MOZ_ASSERT(refCnt > 0);
return refCnt == 1;
}
private:
int refCnt;
};
/**
* RefPtr points to a refcounted thing that has AddRef and Release
* methods to increase/decrease the refcount, respectively. After a
* RefPtr<T> is assigned a T*, the T* can be used through the RefPtr
* as if it were a T*.
*
* A RefPtr can forget its underlying T*, which results in the T*
* being wrapped in a temporary object until the T* is either
* re-adopted from or released by the temporary.
*/
template<typename T>
class RefPtr
{
// To allow them to use unref()
friend class TemporaryRef<T>;
friend class OutParamRef<T>;
struct dontRef {};
public:
RefPtr() : ptr(0) { }
RefPtr(const RefPtr& o) : ptr(ref(o.ptr)) {}
RefPtr(const TemporaryRef<T>& o) : ptr(o.drop()) {}
RefPtr(T* t) : ptr(ref(t)) {}
template<typename U>
RefPtr(const RefPtr<U>& o) : ptr(ref(o.get())) {}
~RefPtr() { unref(ptr); }
RefPtr& operator=(const RefPtr& o) {
assign(ref(o.ptr));
return *this;
}
RefPtr& operator=(const TemporaryRef<T>& o) {
assign(o.drop());
return *this;
}
RefPtr& operator=(T* t) {
assign(ref(t));
return *this;
}
template<typename U>
RefPtr& operator=(const RefPtr<U>& o) {
assign(ref(o.get()));
return *this;
}
TemporaryRef<T> forget() {
T* tmp = ptr;
ptr = 0;
return TemporaryRef<T>(tmp, dontRef());
}
T* get() const { return ptr; }
operator T*() const { return ptr; }
T* operator->() const { return ptr; }
T& operator*() const { return *ptr; }
template<typename U>
operator TemporaryRef<U>() { return forget(); }
private:
void assign(T* t) {
unref(ptr);
ptr = t;
}
T* ptr;
static MOZ_ALWAYS_INLINE T* ref(T* t) {
if (t) {
t->AddRef();
}
return t;
}
static MOZ_ALWAYS_INLINE void unref(T* t) {
if (t) {
t->Release();
}
}
};
/**
* TemporaryRef<T> represents an object that holds a temporary
* reference to a T. TemporaryRef objects can't be manually ref'd or
* unref'd (being temporaries, not lvalues), so can only relinquish
* references to other objects, or unref on destruction.
*/
template<typename T>
class TemporaryRef
{
// To allow it to construct TemporaryRef from a bare T*
friend class RefPtr<T>;
typedef typename RefPtr<T>::dontRef dontRef;
public:
TemporaryRef(T* t) : ptr(RefPtr<T>::ref(t)) {}
TemporaryRef(const TemporaryRef& o) : ptr(o.drop()) {}
template<typename U>
TemporaryRef(const TemporaryRef<U>& o) : ptr(o.drop()) {}
~TemporaryRef() { RefPtr<T>::unref(ptr); }
T* drop() const {
T* tmp = ptr;
ptr = 0;
return tmp;
}
private:
TemporaryRef(T* t, const dontRef&) : ptr(t) {}
mutable T* ptr;
TemporaryRef();
TemporaryRef& operator=(const TemporaryRef&);
};
/**
* OutParamRef is a wrapper that tracks a refcounted pointer passed as
* an outparam argument to a function. OutParamRef implements COM T**
* outparam semantics: this requires the callee to AddRef() the T*
* returned through the T** outparam on behalf of the caller. This
* means the caller (through OutParamRef) must Release() the old
* object contained in the tracked RefPtr. It's OK if the callee
* returns the same T* passed to it through the T** outparam, as long
* as the callee obeys the COM discipline.
*
* Prefer returning TemporaryRef<T> from functions over creating T**
* outparams and passing OutParamRef<T> to T**. Prefer RefPtr<T>*
* outparams over T** outparams.
*/
template<typename T>
class OutParamRef
{
friend OutParamRef byRef<T>(RefPtr<T>&);
public:
~OutParamRef() {
RefPtr<T>::unref(refPtr.ptr);
refPtr.ptr = tmp;
}
operator T**() { return &tmp; }
private:
OutParamRef(RefPtr<T>& p) : refPtr(p), tmp(p.get()) {}
RefPtr<T>& refPtr;
T* tmp;
OutParamRef();
OutParamRef& operator=(const OutParamRef&);
};
/**
* byRef cooperates with OutParamRef to implement COM outparam semantics.
*/
template<typename T>
OutParamRef<T>
byRef(RefPtr<T>& ptr)
{
return OutParamRef<T>(ptr);
}
} // namespace mozilla
#endif // mozilla_RefPtr_h_
#if 0
// Command line that builds these tests
//
// cp RefPtr.h test.cc && g++ -g -Wall -pedantic -DDEBUG -o test test.cc && ./test
using namespace mozilla;
struct Foo : public RefCounted<Foo>
{
Foo() : dead(false) { }
~Foo() {
MOZ_ASSERT(!dead);
dead = true;
numDestroyed++;
}
bool dead;
static int numDestroyed;
};
int Foo::numDestroyed;
struct Bar : public Foo { };
TemporaryRef<Foo>
NewFoo()
{
return RefPtr<Foo>(new Foo());
}
TemporaryRef<Foo>
NewBar()
{
return new Bar();
}
void
GetNewFoo(Foo** f)
{
*f = new Bar();
// Kids, don't try this at home
(*f)->AddRef();
}
void
GetPassedFoo(Foo** f)
{
// Kids, don't try this at home
(*f)->AddRef();
}
void
GetNewFoo(RefPtr<Foo>* f)
{
*f = new Bar();
}
void
GetPassedFoo(RefPtr<Foo>* f)
{}
TemporaryRef<Foo>
GetNullFoo()
{
return 0;
}
int
main(int argc, char** argv)
{
// This should blow up
// Foo* f = new Foo(); delete f;
MOZ_ASSERT(0 == Foo::numDestroyed);
{
RefPtr<Foo> f = new Foo();
MOZ_ASSERT(f->refCount() == 1);
}
MOZ_ASSERT(1 == Foo::numDestroyed);
{
RefPtr<Foo> f1 = NewFoo();
RefPtr<Foo> f2(NewFoo());
MOZ_ASSERT(1 == Foo::numDestroyed);
}
MOZ_ASSERT(3 == Foo::numDestroyed);
{
RefPtr<Foo> b = NewBar();
MOZ_ASSERT(3 == Foo::numDestroyed);
}
MOZ_ASSERT(4 == Foo::numDestroyed);
{
RefPtr<Foo> f1;
{
f1 = new Foo();
RefPtr<Foo> f2(f1);
RefPtr<Foo> f3 = f2;
MOZ_ASSERT(4 == Foo::numDestroyed);
}
MOZ_ASSERT(4 == Foo::numDestroyed);
}
MOZ_ASSERT(5 == Foo::numDestroyed);
{
RefPtr<Foo> f = new Foo();
f.forget();
MOZ_ASSERT(6 == Foo::numDestroyed);
}
{
RefPtr<Foo> f = new Foo();
GetNewFoo(byRef(f));
MOZ_ASSERT(7 == Foo::numDestroyed);
}
MOZ_ASSERT(8 == Foo::numDestroyed);
{
RefPtr<Foo> f = new Foo();
GetPassedFoo(byRef(f));
MOZ_ASSERT(8 == Foo::numDestroyed);
}
MOZ_ASSERT(9 == Foo::numDestroyed);
{
RefPtr<Foo> f = new Foo();
GetNewFoo(&f);
MOZ_ASSERT(10 == Foo::numDestroyed);
}
MOZ_ASSERT(11 == Foo::numDestroyed);
{
RefPtr<Foo> f = new Foo();
GetPassedFoo(&f);
MOZ_ASSERT(11 == Foo::numDestroyed);
}
MOZ_ASSERT(12 == Foo::numDestroyed);
{
RefPtr<Foo> f1 = new Bar();
}
MOZ_ASSERT(13 == Foo::numDestroyed);
{
RefPtr<Foo> f = GetNullFoo();
MOZ_ASSERT(13 == Foo::numDestroyed);
}
MOZ_ASSERT(13 == Foo::numDestroyed);
return 0;
}
#endif
