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.
  //
  // The following only applies to changes made to this file as part of YugaByte development.
  //
  // Portions Copyright (c) YugaByte, Inc.
  //
  // Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  // in compliance with the License.  You may obtain a copy of the License at
  //
  // http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software distributed under the License
  // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  // or implied.  See the License for the specific language governing permissions and limitations
  // under the License.
  //
  
  #ifndef YB_GUTIL_REF_COUNTED_H
  #define YB_GUTIL_REF_COUNTED_H
  
  #include <atomic>
  #include <ostream>
  #include <utility>
  
  #ifndef NDEBUG
  #include <string>
  #endif
  
  #include <typeinfo>
  
  #include "yb/gutil/atomicops.h"
  #include "yb/gutil/port.h"
  #include "yb/gutil/threading/thread_collision_warner.h"
  
  namespace yb {
  namespace subtle {
  
  // TODO: switch to std::atomic<int32_t>
  typedef std::atomic<intptr_t> 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;
  
  #ifndef NDEBUG
    intptr_t GetRefCountForDebugging() const { return ref_count_; }
  #endif
  
   private:
    mutable intptr_t 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() = default;
    ~RefCountedThreadSafeBase();
  
    void AddRef() const;
  
    // Returns true if the object should self-delete.
    bool Release() const;
  
  #ifndef NDEBUG
    intptr_t GetRefCountForDebugging() const {
      return ref_count_.load(std::memory_order_relaxed);
    }
  #endif
  
   private:
    mutable AtomicRefCount ref_count_{0};
  #ifndef NDEBUG
    mutable bool in_dtor_ = false;
  #endif
  
    DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
  };
  
  // ------------------------------------------------------------------------------------------------
  // A facility for debugging where exactly reference counts are incremented and decremented.
  
  #ifdef NDEBUG
  
  // No-op in release mode.
  #define INVOKE_REF_COUNTED_DEBUG_HOOK(event_type)
  
  #else
  
  extern bool g_ref_counted_debug_enabled;
  
  // This callback is called for type names matching the regex to do the actual reporting of refcount
  // increase/decrease.
  // Parameters: type name, instance pointer, current refcount, refcount delta (+1 or -1).
  typedef void RefCountedDebugFn(const char*, const void*, int32_t, int32_t);
  
  // Configure logging on reference count increments/decrements.
  // type_name_regex - regular expression for type names that we'll be logging for.
  // debug_fn - a function to log a refcount increment/decrement event.
  void InitRefCountedDebugging(const std::string& type_name_regex, RefCountedDebugFn* debug_fn);
  
  void RefCountedDebugHook(const char* type_name,
                           const void* this_ptr,
                           int64_t current_refcount,
                           int64_t ref_delta);
  
  #define INVOKE_REF_COUNTED_DEBUG_HOOK(ref_delta) \
      do { \
        if (subtle::g_ref_counted_debug_enabled) { \
          subtle::RefCountedDebugHook(typeid(*this).name(), this, GetRefCountForDebugging(), \
                                      ref_delta); \
        } \
      } while (0)
  
  #endif
  
  }  // 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 accidentally while there are references to it.ging();
  template <class T>
  class RefCounted : public subtle::RefCountedBase {
   public:
    RefCounted() {}
  
    void AddRef() const {
      INVOKE_REF_COUNTED_DEBUG_HOOK(1);
      subtle::RefCountedBase::AddRef();
    }
  
    void Release() const {
      INVOKE_REF_COUNTED_DEBUG_HOOK(-1);
      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 {
      INVOKE_REF_COUNTED_DEBUG_HOOK(1);
      subtle::RefCountedThreadSafeBase::AddRef();
    }
  
    void Release() const {
      INVOKE_REF_COUNTED_DEBUG_HOOK(-1);
      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);
  };
  
  template <class T, typename Traits>
  void intrusive_ptr_add_ref(RefCountedThreadSafe<T, Traits>* px) {
    px->AddRef();
  }
  
  template <class T, typename Traits>
  void intrusive_ptr_release(RefCountedThreadSafe<T, Traits>* px) {
    px->Release();
  }
  
  //
  // A thread-safe wrapper for some piece of data so we can place other
  // things in scoped_refptrs<>.
  //
  template<typename T>
  class RefCountedData
      : public yb::RefCountedThreadSafe< yb::RefCountedData<T> > {
   public:
    RefCountedData() : data() {}
    explicit RefCountedData(const T& in_value) : data(in_value) {}
  
    T data;
  
   private:
    friend class yb::RefCountedThreadSafe<yb::RefCountedData<T> >;
    ~RefCountedData() {}
  };
  
  }  // namespace yb
  
  //
  // 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.
  //   }
  //
  
  #ifndef NDEBUG
  void ScopedRefPtrCheck(bool);
  #else
  inline void ScopedRefPtrCheck(bool) {}
  #endif
  
  
  template <class T>
  class scoped_refptr {
   public:
    typedef T element_type;
  
    scoped_refptr() : ptr_(NULL) {
    }
  
    scoped_refptr(T* p) : ptr_(p) { // NOLINT
      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_; }
  
    T* detach() {
      T *temp = ptr_;
      ptr_ = nullptr;
      return temp;
    }
  
    explicit operator bool() const { return ptr_ != nullptr; }
  
    bool operator!() const { return ptr_ == nullptr; }
  
    T* operator->() const {
      ScopedRefPtrCheck(ptr_ != nullptr);
      return ptr_;
    }
  
    T& operator*() const {
      ScopedRefPtrCheck(ptr_ != nullptr);
      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 std::unique_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);
  }
  
  template<class T, class... Args>
  scoped_refptr<T> make_scoped_refptr(Args&&... args) {
    return scoped_refptr<T>(new T(std::forward<Args>(args)...));
  }
  
  // equal_to and hash implementations for templated scoped_refptrs suitable for
  // use with STL unordered_* containers.
  struct ScopedRefPtrEqualsFunctor {
    template <class T>
    bool operator()(const scoped_refptr<T>& x, const scoped_refptr<T>& y) const {
      return x.get() == y.get();
    }
  };
  
  struct ScopedRefPtrHashFunctor {
    template <class T>
    size_t operator()(const scoped_refptr<T>& p) const {
      return reinterpret_cast<size_t>(p.get());
    }
  };
  
  template<class T>
  bool operator==(const scoped_refptr<T>& lhs, std::nullptr_t) {
    return !lhs;
  }
  
  template<class T>
  bool operator!=(const scoped_refptr<T>& lhs, std::nullptr_t) {
    return static_cast<bool>(lhs);
  }
  
  template<class T>
  bool operator==(std::nullptr_t, const scoped_refptr<T>& rhs) {
    return !rhs;
  }
  
  template<class T>
  bool operator!=(std::nullptr_t, const scoped_refptr<T>& rhs) {
    return static_cast<bool>(rhs);
  }
  
  template<class T>
  std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& ptr) {
    return out << ptr.get();
  }
  
  template <class T, class U>
  bool operator==(const scoped_refptr<T>& lhs, const scoped_refptr<U>& rhs) {
    return lhs.get() == rhs.get();
  }
  
  template <class T, class U>
  bool operator!=(const scoped_refptr<T>& lhs, const scoped_refptr<U>& rhs) {
    return lhs.get() != rhs.get();
  }
  
  #undef INVOKE_REF_COUNTED_DEBUG_HOOK
  
  #endif // YB_GUTIL_REF_COUNTED_H
  