1/*
2 * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 */
24
25#ifndef SHARE_OOPS_WEAKHANDLE_HPP
26#define SHARE_OOPS_WEAKHANDLE_HPP
27
28#include "oops/oop.hpp"
29#include "runtime/handles.hpp"
30
31class outputStream;
32class OopStorage;
33
34// A WeakHandle is a pointer to an oop that is stored in an OopStorage that is
35// processed weakly by GC. The runtime structures that point to the oop must
36// either peek or resolve the oop, the latter will keep the oop alive for
37// the GC cycle. The runtime structures that reference the oop must test
38// if the value is NULL. If it is NULL, it has been cleaned out by GC.
39// This is the vm version of jweak but has different GC lifetimes and policies,
40// depending on the type.
41
42enum WeakHandleType { vm_class_loader_data, vm_string_table_data, vm_resolved_method_table_data };
43
44template <WeakHandleType T>
45class WeakHandle {
46 public:
47 private:
48 oop* _obj;
49
50 WeakHandle(oop* w) : _obj(w) {}
51 static OopStorage* get_storage();
52 public:
53 WeakHandle() : _obj(NULL) {} // needed for init
54
55 static WeakHandle create(Handle obj);
56 inline oop resolve() const;
57 inline oop peek() const;
58 void release() const;
59 bool is_null() const { return _obj == NULL; }
60
61 void replace(oop with_obj);
62
63 void print() const;
64 void print_on(outputStream* st) const;
65};
66
67#endif // SHARE_OOPS_WEAKHANDLE_HPP
68