/*

 * Copyright (c) 2018, 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_VM_OOPS_WEAKHANDLE_HPP

#define SHARE_VM_OOPS_WEAKHANDLE_HPP

#include "oops/oop.hpp"

#include "runtime/handles.hpp"

class outputStream;

class OopStorage;

// A WeakHandle is a pointer to an oop that is stored in an OopStorage that is

// processed weakly by GC.  The runtime structures that point to the oop must

// either peek or resolve the oop, the latter will keep the oop alive for

// the GC cycle.  The runtime structures that reference the oop must test

// if the value is NULL.  If it is NULL, it has been cleaned out by GC.

// This is the vm version of jweak but has different GC lifetimes and policies,

// depending on the type.

template <WeakHandleType T>

class WeakHandle {

 public:

 private:

  oop* _obj;

  WeakHandle(oop* w) : _obj(w) {}

  static OopStorage* get_storage();

 public:

  WeakHandle() : _obj(NULL) {} // needed for init

  static WeakHandle create(Handle obj);

  inline oop resolve() const;

  inline oop peek() const;

  void release() const;

  bool is_null() const { return _obj == NULL; }

  void replace(oop with_obj);

  void print() const;

  void print_on(outputStream* st) const;

};

typedef WeakHandle<vm_class_loader_data> ClassLoaderWeakHandle;

#endif // SHARE_VM_OOPS_WEAKHANDLE_HPP