// 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 BUTIL_MEMORY_REF_COUNTED_H_

#define BUTIL_MEMORY_REF_COUNTED_H_

#include <cassert>

#include "butil/atomic_ref_count.h"

#include "butil/base_export.h"

#include "butil/compiler_specific.h"

#ifndef NDEBUG

#include "butil/logging.h"

#endif

#include "butil/threading/thread_collision_warner.h"

namespace butil {

namespace subtle {

class BUTIL_EXPORT RefCountedBase {

 public:

  bool HasOneRef() const { return ref_count_ == 1; }

 protected:

  RefCountedBase()

      : ref_count_(0)

      , in_dtor_(false)

      {

  }

  ~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_;

#if defined(__clang__)

  mutable bool ALLOW_UNUSED  in_dtor_;

#else

  mutable bool in_dtor_;

#endif

  DFAKE_MUTEX(add_release_);

  DISALLOW_COPY_AND_ASSIGN(RefCountedBase);

};

class BUTIL_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_;

#if defined(__clang__)

  mutable bool ALLOW_UNUSED  in_dtor_;

#else

  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 butil::RefCounted<MyFoo> {

//    ...

//    private:

//     friend class butil::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);

};

// 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 butil::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 butil::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 butil::RefCountedThreadSafe< butil::RefCountedData<T> > {

 public:

  RefCountedData() : data() {}

  RefCountedData(const T& in_value) : data(in_value) {}

  T data;

 private:

  friend class butil::RefCountedThreadSafe<butil::RefCountedData<T> >;

  ~RefCountedData() {}

};

}  // namespace butil

//

// 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(scoped_refptr<T>&& r) noexcept {

    ptr_ = r.ptr_;

    r.ptr_ = nullptr;

  }

  template <typename U>

  scoped_refptr(scoped_refptr<U>&& r) noexcept {

    ptr_ = r.ptr_;

    r.ptr_ = nullptr;

  }

  ~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_);

  }

  // Release ownership of ptr_, keeping its reference counter unchanged.

  T* release() WARN_UNUSED_RESULT {

      T* saved_ptr = NULL;

      swap(&saved_ptr);

      return saved_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  // BUTIL_MEMORY_REF_COUNTED_H_