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+// Copyright (c) 2011 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_
+#pragma once
+
+#include "base/atomic_ref_count.h"
+#include "base/base_export.h"
+#include "base/threading/thread_collision_warner.h"
+
+namespace base {
+
+namespace subtle {
+
+class BASE_EXPORT RefCountedBase {
+ public:
+ static bool ImplementsThreadSafeReferenceCounting() { return false; }
+
+ bool HasOneRef() const { return ref_count_ == 1; }
+
+ protected:
+ RefCountedBase();
+ ~RefCountedBase();
+
+ void AddRef() const;
+
+ // Returns true if the object should self-delete.
+ bool Release() const;
+
+ 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:
+ static bool ImplementsThreadSafeReferenceCounting() { return true; }
+
+ 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() { }
+ ~RefCounted() { }
+
+ void AddRef() const {
+ subtle::RefCountedBase::AddRef();
+ }
+
+ void Release() const {
+ if (subtle::RefCountedBase::Release()) {
+ delete static_cast<const T*>(this);
+ }
+ }
+
+ 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() { }
+ ~RefCountedThreadSafe() { }
+
+ void AddRef() const {
+ subtle::RefCountedThreadSafeBase::AddRef();
+ }
+
+ void Release() const {
+ if (subtle::RefCountedThreadSafeBase::Release()) {
+ Traits::Destruct(static_cast<const T*>(this));
+ }
+ }
+
+ private:
+ friend struct DefaultRefCountedThreadSafeTraits<T>;
+ static void DeleteInternal(const T* x) { delete x; }
+
+ DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
+};
+
+//
+// A wrapper for some piece of data so we can place other things in
+// scoped_refptrs<>.
+//
+template<typename T>
+class RefCountedData : public base::RefCounted< base::RefCountedData<T> > {
+ public:
+ RefCountedData() : data() {}
+ RefCountedData(const T& in_value) : data(in_value) {}
+
+ T data;
+};
+
+} // 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:
+ 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_; }
+ operator T*() const { return ptr_; }
+ T* operator->() const { return ptr_; }
+
+ // Release a pointer.
+ // The return value is the current pointer held by this object.
+ // If this object holds a NULL pointer, the return value is NULL.
+ // After this operation, this object will hold a NULL pointer,
+ // and will not own the object any more.
+ T* release() {
+ T* retVal = ptr_;
+ ptr_ = NULL;
+ return retVal;
+ }
+
+ scoped_refptr<T>& operator=(T* p) {
+ // AddRef first so that self assignment should work
+ if (p)
+ p->AddRef();
+ if (ptr_ )
+ ptr_ ->Release();
+ ptr_ = p;
+ 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_