ppapi/native_client/src/include/ref_counted.h

// 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 NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_
#define NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_

#include "native_client/src/shared/platform/nacl_sync_checked.h"

namespace nacl {

namespace subtle {

class RefCountedBase {
 public:
  bool HasOneRef() const {
    nacl::ScopedNaClMutexLock ml(&mu_);
    return (ref_count_ == 1);
  }

 protected:
  RefCountedBase() : ref_count_(0) {
    NaClXMutexCtor(&mu_);
  }
  ~RefCountedBase() {
    NaClMutexDtor(&mu_);
  }

  void AddRef() const {
    nacl::ScopedNaClMutexLock ml(&mu_);
    ++ref_count_;
  }

  // Returns true if the object should self-delete.
  bool Release() const {
    nacl::ScopedNaClMutexLock ml(&mu_);
    bool should_delete = (--ref_count_ == 0);
    return should_delete;
  }

 private:
  mutable int ref_count_;
  mutable struct NaClMutex mu_;

  RefCountedBase(const RefCountedBase&);
  void operator=(const RefCountedBase&);
};

}  // 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 nacl::RefCounted<MyFoo> {
//    ...
//    private:
//     friend class nacl::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 RefCountedThreadSafe : public subtle::RefCountedBase {
 public:
  RefCountedThreadSafe() {}

  void AddRef() const {
    subtle::RefCountedBase::AddRef();
  }

  void Release() const {
    if (subtle::RefCountedBase::Release()) {
      delete static_cast<const T*>(this);
    }
  }

 protected:
  ~RefCountedThreadSafe() {}

 private:
  RefCountedThreadSafe(const RefCountedThreadSafe<T>&);
  void operator=(const RefCountedThreadSafe<T>&);
};

//
// A wrapper for some piece of data so we can place other things in
// scoped_refptrs<>.
//
template<typename T>
class RefCountedData
    : public RefCountedThreadSafe<RefCountedData<T> > {
 public:
  RefCountedData() : data() {}
  RefCountedData(const T& in_value) : data(in_value) {}

  T data;
};

}  // namespace nacl

//
// 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_((T*)0) {}

  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_ = (void*)0;
    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  // NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_