// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_MEMORY_REF_COUNTED_H_
#define BASE_MEMORY_REF_COUNTED_H_
#include <cassert>
#include "base/atomic_ref_count.h"
#include "base/base_export.h"
#include "base/compiler_specific.h"
#ifndef NDEBUG
#include "base/logging.h"
#endif
#include "base/threading/thread_collision_warner.h"
namespace base {
namespace subtle {
class BASE_EXPORT RefCountedBase {
public:
bool HasOneRef() const { return ref_count_ == 1; }
protected:
RefCountedBase()
: ref_count_(0)
#ifndef NDEBUG
, in_dtor_(false)
#endif
{
}
~RefCountedBase() {
#ifndef NDEBUG
DCHECK(in_dtor_) << "RefCounted object deleted without calling Release()";
#endif
}
void AddRef() const {
// TODO(maruel): Add back once it doesn't assert 500 times/sec.
// Current thread books the critical section "AddRelease"
// without release it.
// DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#ifndef NDEBUG
DCHECK(!in_dtor_);
#endif
++ref_count_;
}
// Returns true if the object should self-delete.
bool Release() const {
// TODO(maruel): Add back once it doesn't assert 500 times/sec.
// Current thread books the critical section "AddRelease"
// without release it.
// DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#ifndef NDEBUG
DCHECK(!in_dtor_);
#endif
if (--ref_count_ == 0) {
#ifndef NDEBUG
in_dtor_ = true;
#endif
return true;
}
return false;
}
private:
mutable int ref_count_;
#ifndef NDEBUG
mutable bool in_dtor_;
#endif
DFAKE_MUTEX(add_release_);
DISALLOW_COPY_AND_ASSIGN(RefCountedBase);
};
class BASE_EXPORT RefCountedThreadSafeBase {
public:
bool HasOneRef() const;
protected:
RefCountedThreadSafeBase();
~RefCountedThreadSafeBase();
void AddRef() const;
// Returns true if the object should self-delete.
bool Release() const;
private:
mutable AtomicRefCount ref_count_;
#ifndef NDEBUG
mutable bool in_dtor_;
#endif
DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
};
} // namespace subtle
//
// A base class for reference counted classes. Otherwise, known as a cheap
// knock-off of WebKit's RefCounted<T> class. To use this guy just extend your
// class from it like so:
//
// class MyFoo : public base::RefCounted<MyFoo> {
// ...
// private:
// friend class base::RefCounted<MyFoo>;
// ~MyFoo();
// };
//
// You should always make your destructor private, to avoid any code deleting
// the object accidently while there are references to it.
template <class T>
class RefCounted : public subtle::RefCountedBase {
public:
RefCounted() {}
void AddRef() const {
subtle::RefCountedBase::AddRef();
}
void Release() const {
if (subtle::RefCountedBase::Release()) {
delete static_cast<const T*>(this);
}
}
protected:
~RefCounted() {}
private:
DISALLOW_COPY_AND_ASSIGN(RefCounted<T>);
};
// Forward declaration.
template <class T, typename Traits> class RefCountedThreadSafe;
// Default traits for RefCountedThreadSafe<T>. Deletes the object when its ref
// count reaches 0. Overload to delete it on a different thread etc.
template<typename T>
struct DefaultRefCountedThreadSafeTraits {
static void Destruct(const T* x) {
// Delete through RefCountedThreadSafe to make child classes only need to be
// friend with RefCountedThreadSafe instead of this struct, which is an
// implementation detail.
RefCountedThreadSafe<T,
DefaultRefCountedThreadSafeTraits>::DeleteInternal(x);
}
};
//
// A thread-safe variant of RefCounted<T>
//
// class MyFoo : public base::RefCountedThreadSafe<MyFoo> {
// ...
// };
//
// If you're using the default trait, then you should add compile time
// asserts that no one else is deleting your object. i.e.
// private:
// friend class base::RefCountedThreadSafe<MyFoo>;
// ~MyFoo();
template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T> >
class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
public:
RefCountedThreadSafe() {}
void AddRef() const {
subtle::RefCountedThreadSafeBase::AddRef();
}
void Release() const {
if (subtle::RefCountedThreadSafeBase::Release()) {
Traits::Destruct(static_cast<const T*>(this));
}
}
protected:
~RefCountedThreadSafe() {}
private:
friend struct DefaultRefCountedThreadSafeTraits<T>;
static void DeleteInternal(const T* x) { delete x; }
DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
};
//
// A thread-safe wrapper for some piece of data so we can place other
// things in scoped_refptrs<>.
//
template<typename T>
class RefCountedData
: public base::RefCountedThreadSafe< base::RefCountedData<T> > {
public:
RefCountedData() : data() {}
RefCountedData(const T& in_value) : data(in_value) {}
T data;
private:
friend class base::RefCountedThreadSafe<base::RefCountedData<T> >;
~RefCountedData() {}
};
} // namespace base
//
// A smart pointer class for reference counted objects. Use this class instead
// of calling AddRef and Release manually on a reference counted object to
// avoid common memory leaks caused by forgetting to Release an object
// reference. Sample usage:
//
// class MyFoo : public RefCounted<MyFoo> {
// ...
// };
//
// void some_function() {
// scoped_refptr<MyFoo> foo = new MyFoo();
// foo->Method(param);
// // |foo| is released when this function returns
// }
//
// void some_other_function() {
// scoped_refptr<MyFoo> foo = new MyFoo();
// ...
// foo = NULL; // explicitly releases |foo|
// ...
// if (foo)
// foo->Method(param);
// }
//
// The above examples show how scoped_refptr<T> acts like a pointer to T.
// Given two scoped_refptr<T> classes, it is also possible to exchange
// references between the two objects, like so:
//
// {
// scoped_refptr<MyFoo> a = new MyFoo();
// scoped_refptr<MyFoo> b;
//
// b.swap(a);
// // now, |b| references the MyFoo object, and |a| references NULL.
// }
//
// To make both |a| and |b| in the above example reference the same MyFoo
// object, simply use the assignment operator:
//
// {
// scoped_refptr<MyFoo> a = new MyFoo();
// scoped_refptr<MyFoo> b;
//
// b = a;
// // now, |a| and |b| each own a reference to the same MyFoo object.
// }
//
template <class T>
class scoped_refptr {
public:
typedef T element_type;
scoped_refptr() : ptr_(NULL) {
}
scoped_refptr(T* p) : ptr_(p) {
if (ptr_)
ptr_->AddRef();
}
scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
if (ptr_)
ptr_->AddRef();
}
template <typename U>
scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
if (ptr_)
ptr_->AddRef();
}
~scoped_refptr() {
if (ptr_)
ptr_->Release();
}
T* get() const { return ptr_; }
// Allow scoped_refptr<C> to be used in boolean expression
// and comparison operations.
operator T*() const { return ptr_; }
T* operator->() const {
assert(ptr_ != NULL);
return ptr_;
}
scoped_refptr<T>& operator=(T* p) {
// AddRef first so that self assignment should work
if (p)
p->AddRef();
T* old_ptr = ptr_;
ptr_ = p;
if (old_ptr)
old_ptr->Release();
return *this;
}
scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
return *this = r.ptr_;
}
template <typename U>
scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
return *this = r.get();
}
void swap(T** pp) {
T* p = ptr_;
ptr_ = *pp;
*pp = p;
}
void swap(scoped_refptr<T>& r) {
swap(&r.ptr_);
}
protected:
T* ptr_;
};
// Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
// having to retype all the template arguments
template <typename T>
scoped_refptr<T> make_scoped_refptr(T* t) {
return scoped_refptr<T>(t);
}
#endif // BASE_MEMORY_REF_COUNTED_H_