text: // 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 <cstddef>
  
  #include "kudu/gutil/atomicops.h"
  #include "kudu/gutil/macros.h"
  #include "kudu/gutil/threading/thread_collision_warner.h"
  
  namespace kudu {
  namespace subtle {
  
  typedef Atomic32 AtomicRefCount;
  
  class RefCountedBase {
   public:
    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 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 RefCounted<MyFoo> {
  //    ...
  //    private:
  //     friend class 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 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 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 kudu::RefCountedThreadSafe< kudu::RefCountedData<T> > {
   public:
    RefCountedData() : data() {}
    RefCountedData(const T& in_value) : data(in_value) {}
  
    T data;
  
   private:
    friend class kudu::RefCountedThreadSafe<kudu::RefCountedData<T> >;
    ~RefCountedData() {}
  };
  
  }  // namespace kudu
  
  //
  // 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();
    }
  
    template <typename U>
    scoped_refptr(scoped_refptr<U>&& r) : ptr_(r.get()) {
      r.ptr_ = nullptr;
    }
  
    ~scoped_refptr() {
      if (ptr_)
        ptr_->Release();
    }
  
    T* get() const { return ptr_; }
  
  // The following is disabled in Cloudera's version of this file since it's
  // relatively dangerous. Chromium is planning on doing the same in their
  // tree, but hasn't done so yet. See http://code.google.com/p/chromium/issues/detail?id=110610
  #if SCOPED_REFPTR_ALLOW_IMPLICIT_CONVERSION_TO_PTR
    // Allow scoped_refptr<C> to be used in boolean expression
    // and comparison operations.
    operator T*() const { return ptr_; }
  #else
    typedef T* scoped_refptr::*Testable;
    operator Testable() const { return ptr_ ? &scoped_refptr::ptr_ : NULL; }
  #endif
  
    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();
    }
  
    scoped_refptr<T>& operator=(scoped_refptr<T>&& r) {
      scoped_refptr<T>(r).swap(*this);
      return *this;
    }
  
    template <typename U>
    scoped_refptr<T>& operator=(scoped_refptr<U>&& r) {
      scoped_refptr<T>(r).swap(*this);
      return *this;
    }
  
    void swap(T** pp) {
      T* p = ptr_;
      ptr_ = *pp;
      *pp = p;
    }
  
    void swap(scoped_refptr<T>& r) {
      swap(&r.ptr_);
    }
  
    // Like gscoped_ptr::reset(), drops a reference on the currently held object
    // (if any), and adds a reference to the passed-in object (if not NULL).
    void reset(T* p = NULL) {
      *this = p;
    }
  
   protected:
    T* ptr_;
  
   private:
    template <typename U> friend class scoped_refptr;
  };
  
  // 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);
  }
  
  // equal_to and hash implementations for templated scoped_refptrs suitable for
  // use with STL unordered_* containers.
  template <class T>
  struct ScopedRefPtrEqualToFunctor {
    bool operator()(const scoped_refptr<T>& x, const scoped_refptr<T>& y) const {
      return x.get() == y.get();
    }
  };
  
  template <class T>
  struct ScopedRefPtrHashFunctor {
    size_t operator()(const scoped_refptr<T>& p) const {
      return reinterpret_cast<size_t>(p.get());
    }
  };
  
  #endif  // BASE_MEMORY_REF_COUNTED_H_
  