1 /*
2 * Copyright (c) 2022, Amazon.com, Inc. 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.
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 #include "precompiled.hpp"
26
27 #include "gc/shenandoah/shenandoahFreeSet.hpp"
28 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
29 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
30 #include "gc/shenandoah/shenandoahOldGC.hpp"
31 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
32 #include "gc/shenandoah/shenandoahGeneration.hpp"
33 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
34 #include "prims/jvmtiTagMap.hpp"
35 #include "utilities/events.hpp"
36
37
38
39
40 ShenandoahOldGC::ShenandoahOldGC(ShenandoahGeneration* generation, ShenandoahSharedFlag& allow_preemption) :
41 ShenandoahConcurrentGC(generation, false), _allow_preemption(allow_preemption) {
42 }
43
44 // Final mark for old-gen is different than for young or old, so we
45 // override the implementation.
46 void ShenandoahOldGC::op_final_mark() {
47
48 ShenandoahHeap* const heap = ShenandoahHeap::heap();
49 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Should be at safepoint");
50 assert(!heap->has_forwarded_objects(), "No forwarded objects on this path");
51
52 if (ShenandoahVerify) {
53 heap->verifier()->verify_roots_no_forwarded();
54 }
55
56 if (!heap->cancelled_gc()) {
57 assert(_mark.generation()->generation_mode() == OLD, "Generation of Old-Gen GC should be OLD");
58 _mark.finish_mark();
59 assert(!heap->cancelled_gc(), "STW mark cannot OOM");
60
61 // Old collection is complete, the young generation no longer needs this
62 // reference to the old concurrent mark so clean it up.
63 heap->young_generation()->set_old_gen_task_queues(nullptr);
64
65 // We need to do this because weak root cleaning reports the number of dead handles
66 JvmtiTagMap::set_needs_cleaning();
67
68 _generation->prepare_regions_and_collection_set(true);
69
70 heap->set_unload_classes(false);
71 heap->prepare_concurrent_roots();
72
73 // Believe verification following old-gen concurrent mark needs to be different than verification following
74 // young-gen concurrent mark, so am commenting this out for now:
75 // if (ShenandoahVerify) {
76 // heap->verifier()->verify_after_concmark();
77 // }
78
79 if (VerifyAfterGC) {
80 Universe::verify();
81 }
82 }
83 }
84
85 bool ShenandoahOldGC::collect(GCCause::Cause cause) {
86 ShenandoahHeap* heap = ShenandoahHeap::heap();
87 assert(!heap->doing_mixed_evacuations(), "Should not start an old gc with pending mixed evacuations");
88 assert(!heap->is_prepare_for_old_mark_in_progress(), "Old regions need to be parseable during concurrent mark.");
89
90 // Enable preemption of old generation mark.
91 _allow_preemption.set();
92
93 // Continue concurrent mark, do not reset regions, do not mark roots, do not collect $200.
94 entry_mark();
95
96 // If we failed to unset the preemption flag, it means another thread has already unset it.
97 if (!_allow_preemption.try_unset()) {
98 // The regulator thread has unset the preemption guard. That thread will shortly cancel
99 // the gc, but the control thread is now racing it. Wait until this thread sees the
100 // cancellation.
101 while (!heap->cancelled_gc()) {
102 SpinPause();
103 }
104 }
105
106 if (heap->cancelled_gc()) {
107 return false;
108 }
109
110 // Complete marking under STW
111 vmop_entry_final_mark();
112
113 // We aren't dealing with old generation evacuation yet. Our heuristic
114 // should not have built a cset in final mark.
115 assert(!heap->is_evacuation_in_progress(), "Old gen evacuations are not supported");
116
117 // Process weak roots that might still point to regions that would be broken by cleanup
118 if (heap->is_concurrent_weak_root_in_progress()) {
119 entry_weak_refs();
120 entry_weak_roots();
121 }
122
123 // Final mark might have reclaimed some immediate garbage, kick cleanup to reclaim
124 // the space. This would be the last action if there is nothing to evacuate.
125 entry_cleanup_early();
126
127 {
128 ShenandoahHeapLocker locker(heap->lock());
129 heap->free_set()->log_status();
130 }
131
132
133 // TODO: Old marking doesn't support class unloading yet
134 // Perform concurrent class unloading
135 // if (heap->unload_classes() &&
136 // heap->is_concurrent_weak_root_in_progress()) {
137 // entry_class_unloading();
138 // }
139
140
141 assert(!heap->is_concurrent_strong_root_in_progress(), "No evacuations during old gc.");
142
143 // We must execute this vm operation if we completed final mark. We cannot
144 // return from here with weak roots in progress. This is not a valid gc state
145 // for any young collections (or allocation failures) that interrupt the old
146 // collection.
147 vmop_entry_final_roots(false);
148
149 return true;
150 }