text: /*
   * Copyright (c) 2017, 2021, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   *
   */
  
  #ifndef SHARE_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
  #define SHARE_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
  
  #include "jfr/utilities/jfrAllocation.hpp"
  #include "runtime/atomic.hpp"
  
  template <typename T>
  class RefCountHandle {
   private:
    const T* _ptr;
  
    RefCountHandle(const T* ptr) : _ptr(ptr) {
      assert(_ptr != NULL, "invariant");
      _ptr->add_ref();
    }
  
   public:
    RefCountHandle() : _ptr(NULL) {}
  
    RefCountHandle(const RefCountHandle<T>& rhs) : _ptr(rhs._ptr) {
      if (_ptr != NULL) {
        _ptr->add_ref();
      }
    }
  
    ~RefCountHandle() {
      if (_ptr != NULL) {
        _ptr->remove_ref();
        _ptr = NULL;
      }
    }
  
    // The copy-and-swap idiom upholds reference counting semantics
    void operator=(RefCountHandle<T> rhs) {
      const T* temp = rhs._ptr;
      rhs._ptr = _ptr;
      _ptr = temp;
    }
  
    bool operator==(const RefCountHandle<T>& rhs) const {
      return _ptr == rhs._ptr;
    }
  
    bool operator!=(const RefCountHandle<T>& rhs) const {
      return !operator==(rhs);
    }
  
    bool valid() const {
      return _ptr != NULL;
    }
  
    const T& operator->() const {
      return *_ptr;
    }
  
    T& operator->() {
      return *const_cast<T*>(_ptr);
    }
  
    static RefCountHandle<T> make(const T* ptr) {
      return ptr;
    }
  };
  
  class SingleThreadedRefCounter {
   private:
    mutable intptr_t _refs;
   public:
    SingleThreadedRefCounter() : _refs(0) {}
  
    void inc() const {
      ++_refs;
    }
  
    bool dec() const {
      return --_refs == 0;
    }
  
    intptr_t current() const {
      return _refs;
    }
  };
  
  class MultiThreadedRefCounter {
   private:
    mutable volatile intptr_t _refs;
   public:
    MultiThreadedRefCounter() : _refs(0) {}
  
    void inc() const {
      Atomic::add(&_refs, 1);
    }
  
    bool dec() const {
      return 0 == Atomic::add(&_refs, (-1));
    }
  
    intptr_t current() const {
     return _refs;
    }
  };
  
  template <typename T, typename RefCountImpl = MultiThreadedRefCounter>
  class RefCountPointer : public JfrCHeapObj {
    template <typename>
    friend class RefCountHandle;
    typedef RefCountHandle<RefCountPointer<T, RefCountImpl> > RefHandle;
   private:
    const T* _ptr;
    mutable RefCountImpl _refs;
  
    // disallow multiple copies
    RefCountPointer(const RefCountPointer<T, RefCountImpl>& rhs);
    void operator=(const RefCountPointer<T, RefCountImpl>& rhs);
  
    ~RefCountPointer() {
      assert(_refs.current() == 0, "invariant");
      delete const_cast<T*>(_ptr);
    }
  
    void add_ref() const {
      _refs.inc();
    }
  
    void remove_ref() const {
      if (_refs.dec()) {
        delete this;
      }
    }
  
    RefCountPointer(const T* ptr) : _ptr(ptr), _refs() {
      assert(_ptr != NULL, "invariant");
    }
  
   public:
    const T* operator->() const {
      return _ptr;
    }
  
    T* operator->() {
      return const_cast<T*>(_ptr);
    }
  
    static RefHandle make(const T* ptr) {
      return RefHandle::make(new RefCountPointer<T, RefCountImpl>(ptr));
    }
  };
  
  #endif // SHARE_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
  