1 /*
 2  * Copyright (c) 2015, 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_INLINE_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
27 
28 #include "gc/shenandoah/shenandoahForwarding.hpp"
29 
30 #include "gc/shenandoah/shenandoahAsserts.hpp"
31 #include "oops/markWord.hpp"
32 #include "runtime/javaThread.hpp"
33 #include "runtime/synchronizer.hpp"
34 
35 inline oop ShenandoahForwarding::get_forwardee_raw(oop obj) {
36   shenandoah_assert_in_heap(NULL, obj);
37   return get_forwardee_raw_unchecked(obj);
38 }
39 
40 inline oop ShenandoahForwarding::get_forwardee_raw_unchecked(oop obj) {
41   // JVMTI and JFR code use mark words for marking objects for their needs.
42   // On this path, we can encounter the "marked" object, but with NULL
43   // fwdptr. That object is still not forwarded, and we need to return
44   // the object itself.
45   markWord mark = obj->mark();
46   if (mark.is_marked()) {
47     HeapWord* fwdptr = (HeapWord*) mark.clear_lock_bits().to_pointer();
48     if (fwdptr != NULL) {
49       return cast_to_oop(fwdptr);
50     }
51   }
52   return obj;
53 }
54 
55 inline oop ShenandoahForwarding::get_forwardee_mutator(oop obj) {
56   // Same as above, but mutator thread cannot ever see NULL forwardee.
57   shenandoah_assert_correct(NULL, obj);
58   assert(Thread::current()->is_Java_thread(), "Must be a mutator thread");
59 
60   markWord mark = obj->mark();
61   if (mark.is_marked()) {
62     HeapWord* fwdptr = (HeapWord*) mark.clear_lock_bits().to_pointer();
63     assert(fwdptr != NULL, "Forwarding pointer is never null here");
64     return cast_to_oop(fwdptr);
65   } else {
66     return obj;
67   }
68 }
69 
70 inline oop ShenandoahForwarding::get_forwardee(oop obj) {
71   shenandoah_assert_correct(NULL, obj);
72   return get_forwardee_raw_unchecked(obj);
73 }
74 
75 inline bool ShenandoahForwarding::is_forwarded(oop obj) {
76   return obj->mark().is_marked();
77 }
78 
79 inline oop ShenandoahForwarding::try_update_forwardee(oop obj, oop update) {
80 
81   markWord old_mark = obj->mark_acquire();
82 
83   if (old_mark.is_marked()) {
84     return cast_to_oop(old_mark.clear_lock_bits().to_pointer());
85   }
86 
87   markWord new_mark = markWord::encode_pointer_as_mark(update);
88   markWord prev_mark = obj->cas_set_mark(new_mark, old_mark, memory_order_conservative);
89   if (prev_mark == old_mark) {
90     return update;
91   } else {
92     assert(prev_mark.is_marked(), "must be forwarded");
93     return cast_to_oop(prev_mark.clear_lock_bits().to_pointer());
94   }
95 }
96 
97 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP