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/markWord.hpp"
29 #include "oops/oop.hpp"
30 #include "utilities/globalDefinitions.hpp"
31 
32 class ShenandoahForwarding {
33 public:
34   /* Gets forwardee from the given object. For a self-forwarded object
35    * (evacuation failure), returns the object itself.
36    */
37   static inline oop get_forwardee(oop obj);
38 
39   /* Gets forwardee from the given object. Only from mutator thread.
40    * For a self-forwarded object, returns the object itself.
41    */
42   static inline oop get_forwardee_mutator(oop obj);
43 
44   /* Returns the raw value from forwardee slot. For a self-forwarded
45    * object, returns the object itself.
46    */
47   static inline oop get_forwardee_raw(oop obj);
48 
49   /* Returns the raw value from forwardee slot without any checks.
50    * Used for quick verification. For a self-forwarded object,
51    * returns the object itself.
52    */
53   static inline oop get_forwardee_raw_unchecked(oop obj);
54 
55   /**
56    * Returns true if the object is forwarded (including self-forwarded),
57    * false otherwise.
58    */
59   static inline bool is_forwarded(oop obj);
60 
61   /**
62    * Returns true iff obj has been self-forwarded (i.e. evacuation has
63    * failed for this object in the current cycle).
64    */
65   static inline bool is_self_forwarded(oop obj);
66 
67   /* Tries to atomically update forwardee in $holder object to $update.
68    * Assumes $holder points at itself.
69    * Asserts $holder is in from-space.
70    * Asserts $update is in to-space.
71    *
72    * Returns the new object 'update' upon success, or
73    * the new forwardee that a competing thread installed. If another
74    * thread self-forwarded the object, returns the object itself.
75    */
76   static inline oop try_update_forwardee(oop obj, oop update);
77 
78   /* Tries to atomically self-forward obj. Used by the evacuation path
79    * when the copy allocation fails: the failing thread installs the
80    * self-forwarded bit so other threads see the object as "already
81    * handled" and return it unchanged.
82    *
83    * Returns nullptr on success (we installed the self-forward), or
84    * the winning forwardee when another thread raced ahead (either a
85    * real forwardee pointing at a copy, or obj itself if the winner
86    * also self-forwarded).
87    */
88   static inline oop try_forward_to_self(oop obj, markWord old_mark);
89 
90   static inline size_t size(oop obj);
91   static inline Klass* klass(oop obj);
92 };
93 
94 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP