1 /*
 2  * Copyright (c) 2013, 2019, Red Hat, Inc. 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.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  *
23  */
24 
25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
27 
28 #include "oops/oop.hpp"
29 #include "utilities/globalDefinitions.hpp"
30 
31 class ShenandoahForwarding {
32 private:
33   static const uintptr_t FWDED_HASH_TRANSITION = 0b111;
34 
35 public:
36   /* Gets forwardee from the given object.
37    */
38   static inline oop get_forwardee(oop obj);
39 
40   /* Gets forwardee from the given object. Only from mutator thread.
41    */
42   static inline oop get_forwardee_mutator(oop obj);
43 
44   /* Returns the raw value from forwardee slot.
45    */
46   static inline oop get_forwardee_raw(oop obj);
47 
48   /* Returns the raw value from forwardee slot without any checks.
49    * Used for quick verification.
50    */
51   static inline oop get_forwardee_raw_unchecked(oop obj);
52 
53   /**
54    * Returns true if the object is forwarded, false otherwise.
55    */
56   static inline bool is_forwarded(oop obj);
57   static inline bool is_forwarded(markWord m);
58 
59   /* Tries to atomically update forwardee in $holder object to $update.
60    * Assumes $holder points at itself.
61    * Asserts $holder is in from-space.
62    * Asserts $update is in to-space.
63    *
64    * Returns the new object 'update' upon success, or
65    * the new forwardee that a competing thread installed.
66    */
67   static inline oop try_update_forwardee(oop obj, oop update);
68 
69   static inline size_t size(oop obj);
70   static inline Klass* klass(oop obj);
71 };
72 
73 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP