1 /*
2 * Copyright (c) 2014, Oracle and/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_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP
27
28 #include "gc_implementation/g1/g1BiasedArray.hpp"
29 #include "memory/allocation.hpp"
30
31 typedef int8_t in_cset_state_t;
32
33 // Helper class used to examine in_cset_t values.
34 class InCSetState : AllStatic {
35 public:
36 enum {
37 // Selection of the values were driven to micro-optimize the encoding and
38 // frequency of the checks.
39 // The most common check is whether the region is in the collection set or not.
40 // This encoding allows us to use an != 0 check which in some architectures
41 // (x86*) can be encoded slightly more efficently than a normal comparison
42 // against zero.
43 // The same situation occurs when checking whether the region is humongous
44 // or not, which is encoded by values < 0.
45 // The other values are simply encoded in increasing generation order, which
46 // makes getting the next generation fast by a simple increment.
47 Humongous = -1, // The region is humongous - note that actually any value < 0 would be possible here.
48 NotInCSet = 0, // The region is not in the collection set.
49 Young = 1, // The region is in the collection set and a young region.
50 Old = 2, // The region is in the collection set and an old region.
51 Num
52 };
53
54 static bool is_not_in_cset(in_cset_state_t state) { return state == NotInCSet; }
55 static bool is_in_cset_or_humongous(in_cset_state_t state) { return state != NotInCSet; }
56 static bool is_in_cset(in_cset_state_t state) { return state > NotInCSet; }
57 static bool is_humongous(in_cset_state_t state) { return state < NotInCSet; }
58 };
59
60 // Instances of this class are used for quick tests on whether a reference points
61 // into the collection set and into which generation or is a humongous object
62 //
63 // Each of the array's elements indicates whether the corresponding region is in
64 // the collection set and if so in which generation, or a humongous region.
65 //
66 // We use this to speed up reference processing during young collection and
67 // quickly reclaim humongous objects. For the latter, by making a humongous region
68 // succeed this test, we sort-of add it to the collection set. During the reference
69 // iteration closures, when we see a humongous region, we then simply mark it as
70 // referenced, i.e. live.
71 class G1InCSetStateFastTestBiasedMappedArray : public G1BiasedMappedArray<in_cset_state_t> {
72 protected:
73 in_cset_state_t default_value() const { return InCSetState::NotInCSet; }
74 public:
75 void set_humongous(uintptr_t index) {
76 assert(get_by_index(index) == default_value(), "should be default");
77 set_by_index(index, InCSetState::Humongous);
78 }
79
80 void clear_humongous(uintptr_t index) {
81 set_by_index(index, InCSetState::NotInCSet);
82 }
83
84 void set_in_young(uintptr_t index) {
85 assert(get_by_index(index) == default_value(), "should be default");
86 set_by_index(index, InCSetState::Young);
87 }
88
89 void set_in_old(uintptr_t index) {
90 assert(get_by_index(index) == default_value(), "should be default");
91 set_by_index(index, InCSetState::Old);
92 }
93
94 bool is_in_cset_or_humongous(HeapWord* addr) const { return InCSetState::is_in_cset_or_humongous(at(addr)); }
95 bool is_in_cset(HeapWord* addr) const { return InCSetState::is_in_cset(at(addr)); }
96 in_cset_state_t at(HeapWord* addr) const { return (in_cset_state_t) get_by_address(addr); }
97 void clear() { G1BiasedMappedArray<in_cset_state_t>::clear(); }
98 };
99
100 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP