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 <utility> // IWYU pragma: keep
  
  #include "gutil/atomicops.h"
  #include "gutil/macros.h"
  #include "gutil/threading/thread_collision_warner.h"
  
  namespace doris {
  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 doris::RefCountedThreadSafe<doris::RefCountedData<T>> {
  public:
      RefCountedData() : data() {}
      RefCountedData(const T& in_value) : data(in_value) {}
  
      T data;
  
  private:
      friend class doris::RefCountedThreadSafe<doris::RefCountedData<T>>;
      ~RefCountedData() {}
  };
  
  } // namespace doris
  
  //
  // 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();
      }
  
      // Copy constructor.
      scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
          if (ptr_) ptr_->AddRef();
      }
  
      // Copy conversion constructor.
      template <typename U>
      scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
          if (ptr_) ptr_->AddRef();
      }
  
      // Move constructor. This is required in addition to the conversion
      // constructor below in order for clang to warn about pessimizing moves.
      scoped_refptr(scoped_refptr&& r) noexcept : ptr_(r.get()) { // NOLINT
          r.ptr_ = nullptr;
      }
  
      // Move conversion constructor.
      template <typename U>
      scoped_refptr(scoped_refptr<U>&& r) noexcept : ptr_(r.get()) { // NOLINT
          r.ptr_ = nullptr;
      }
  
      ~scoped_refptr() {
          if (ptr_) ptr_->Release();
      }
  
      T* get() const { return ptr_; }
  
  // The following is disabled in Kudu'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>(std::move(r)).swap(*this);
          return *this;
      }
  
      template <typename U>
      scoped_refptr<T>& operator=(scoped_refptr<U>&& r) {
          scoped_refptr<T>(std::move(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_
  