1 /*
2 * Copyright (c) 2021, 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 #ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
26 #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
27
28
29 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
30
31 class ShenandoahCollectionSet;
32 class ShenandoahHeapRegion;
33 class ShenandoahOldGeneration;
34
35 class ShenandoahOldHeuristics : public ShenandoahHeuristics {
36
37 private:
38
39 static uint NOT_FOUND;
40
41 // After final marking of the old generation, this heuristic will select
42 // a set of candidate regions to be included in subsequent mixed collections.
43 // The regions are sorted into a `_region_data` array (declared in base
44 // class) in decreasing order of garbage. The heuristic will give priority
45 // to regions containing more garbage.
46
47 // The following members are used to keep track of which candidate regions
48 // have yet to be added to a mixed collection. There is also some special
49 // handling for pinned regions, described further below.
50
51 // This points to the first candidate of the current mixed collection. This
52 // is only used for an assertion when handling pinned regions.
53 debug_only(uint _start_candidate);
54
55 // Pinned regions may not be included in the collection set. Any old regions
56 // which were pinned at the time when old regions were added to the mixed
57 // collection will have been skipped. These regions are still contain garbage,
58 // so we want to include them at the start of the list of candidates for the
59 // _next_ mixed collection cycle. This variable is the index of the _first_
60 // old region which is pinned when the mixed collection set is formed.
61 uint _first_pinned_candidate;
62
63 // This is the index of the last region which is above the garbage threshold.
64 // No regions after this will be considered for inclusion in a mixed collection
65 // set.
66 uint _last_old_collection_candidate;
67
68 // This index points to the first candidate in line to be added to the mixed
69 // collection set. It is updated as regions are added to the collection set.
70 uint _next_old_collection_candidate;
71
72 // This is the last index in the array of old regions which were active at
73 // the end of old final mark.
74 uint _last_old_region;
75
76 // This can be the 'static' or 'adaptive' heuristic.
77 ShenandoahHeuristics* _trigger_heuristic;
78
79 // Flag is set when promotion failure is detected (by gc thread), and cleared when
80 // old generation collection begins (by control thread).
81 volatile bool _promotion_failed;
82
83 // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
84 ShenandoahOldGeneration* _old_generation;
85
86 protected:
87 virtual void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size,
88 size_t free) override;
89
90 public:
91 ShenandoahOldHeuristics(ShenandoahOldGeneration* generation, ShenandoahHeuristics* trigger_heuristic);
92
93 virtual void choose_collection_set(ShenandoahCollectionSet* collection_set, ShenandoahOldHeuristics* old_heuristics) override;
94
95 // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
96 void prepare_for_old_collections();
97
98 // Return true iff the collection set is primed with at least one old-gen region.
99 bool prime_collection_set(ShenandoahCollectionSet* set);
100
101 // How many old-collection candidates have not yet been processed?
102 uint unprocessed_old_collection_candidates();
103
104 // How many old or hidden collection candidates have not yet been processed?
105 uint last_old_collection_candidate_index();
106
107 // Return the next old-collection candidate in order of decreasing amounts of garbage. (We process most-garbage regions
108 // first.) This does not consume the candidate. If the candidate is selected for inclusion in a collection set, then
109 // the candidate is consumed by invoking consume_old_collection_candidate().
110 ShenandoahHeapRegion* next_old_collection_candidate();
111
112 // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
113 void consume_old_collection_candidate();
114
115 // How many old-collection regions were identified at the end of the most recent old-gen mark to require their
116 // unmarked objects to be coalesced and filled?
117 uint last_old_region_index() const;
118
119 // Fill in buffer with all of the old-collection regions that were identified at the end of the most recent old-gen
120 // mark to require their unmarked objects to be coalesced and filled. The buffer array must have at least
121 // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
122 // end of the array.
123 unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
124
125 // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
126 // held by this heuristic for supplying mixed collections.
127 void abandon_collection_candidates();
128
129 // Notify the heuristic of promotion failures. The promotion attempt will be skipped and the object will
130 // be evacuated into the young generation. The collection should complete normally, but we want to schedule
131 // an old collection as soon as possible.
132 void handle_promotion_failure();
133
134 virtual void record_cycle_start() override;
135
136 virtual void record_cycle_end() override;
137
138 virtual bool should_start_gc() override;
139
140 virtual bool should_degenerate_cycle() override;
141
142 virtual void record_success_concurrent(bool abbreviated) override;
143
144 virtual void record_success_degenerated() override;
145
146 virtual void record_success_full() override;
147
148 virtual void record_allocation_failure_gc() override;
149
150 virtual void record_requested_gc() override;
151
152 virtual bool can_unload_classes() override;
153
154 virtual bool can_unload_classes_normal() override;
155
156 virtual bool should_unload_classes() override;
157
158 virtual const char* name() override;
159
160 virtual bool is_diagnostic() override;
161
162 virtual bool is_experimental() override;
163
164 private:
165 void slide_pinned_regions_to_front();
166 };
167
168 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP