1 /*
 2  * Copyright (c) 2018, 2020, 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
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 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
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18  *
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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 
31 class outputStream;
32 class 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 
42 class WeakHandle {
43  public:
44  private:
45   oop* _obj;
46 
47   WeakHandle(oop* w) : _obj(w) {}
48  public:
49   WeakHandle() : _obj(NULL) {} // needed for init
50   WeakHandle(OopStorage* storage, Handle obj);
51   WeakHandle(OopStorage* storage, oop obj);
52 
53   static WeakHandle from_raw(oop* raw);
54   inline oop resolve() const;
55   inline oop peek() const;
56   void release(OopStorage* storage) const;
57   bool is_null() const { return _obj == NULL; }
58 
59   void replace(oop with_obj);
60   oop* raw() { return _obj; }
61 
62   void print() const;
63   void print_on(outputStream* st) const;
64 
65   bool is_empty() const { return _obj == NULL; }
66   oop* ptr_raw() const { return _obj; }
67 };
68 
69 #endif // SHARE_OOPS_WEAKHANDLE_HPP