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