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annotate src/share/vm/gc_implementation/g1/g1StringDedup.hpp @ 20469:dd89808e49ba
8049530: Provide descriptive failure reason for compilation tasks removed for the queue
Reviewed-by: roland, iveresov
author | vlivanov |
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date | Mon, 14 Jul 2014 03:26:52 -0700 |
parents | 1772223a25a2 |
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rev | line source |
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17764 | 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_G1STRINGDEDUP_HPP | |
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP | |
27 | |
28 // | |
29 // String Deduplication | |
30 // | |
31 // String deduplication aims to reduce the heap live-set by deduplicating identical | |
32 // instances of String so that they share the same backing character array. | |
33 // | |
34 // The deduplication process is divided in two main parts, 1) finding the objects to | |
35 // deduplicate, and 2) deduplicating those objects. The first part is done as part of | |
36 // a normal GC cycle when objects are marked or evacuated. At this time a check is | |
37 // applied on each object to check if it is a candidate for deduplication. If so, the | |
38 // object is placed on the deduplication queue for later processing. The second part, | |
39 // processing the objects on the deduplication queue, is a concurrent phase which | |
40 // starts right after the stop-the-wold marking/evacuation phase. This phase is | |
41 // executed by the deduplication thread, which pulls deduplication candidates of the | |
42 // deduplication queue and tries to deduplicate them. | |
43 // | |
44 // A deduplication hashtable is used to keep track of all unique character arrays | |
45 // used by String objects. When deduplicating, a lookup is made in this table to see | |
46 // if there is already an identical character array somewhere on the heap. If so, the | |
47 // String object is adjusted to point to that character array, releasing the reference | |
48 // to the original array allowing it to eventually be garbage collected. If the lookup | |
49 // fails the character array is instead inserted into the hashtable so that this array | |
50 // can be shared at some point in the future. | |
51 // | |
52 // Candidate selection | |
53 // | |
54 // An object is considered a deduplication candidate if all of the following | |
55 // statements are true: | |
56 // | |
57 // - The object is an instance of java.lang.String | |
58 // | |
59 // - The object is being evacuated from a young heap region | |
60 // | |
61 // - The object is being evacuated to a young/survivor heap region and the | |
62 // object's age is equal to the deduplication age threshold | |
63 // | |
64 // or | |
65 // | |
66 // The object is being evacuated to an old heap region and the object's age is | |
67 // less than the deduplication age threshold | |
68 // | |
69 // Once an string object has been promoted to an old region, or its age is higher | |
70 // than the deduplication age threshold, is will never become a candidate again. | |
71 // This approach avoids making the same object a candidate more than once. | |
72 // | |
73 // Interned strings are a bit special. They are explicitly deduplicated just before | |
74 // being inserted into the StringTable (to avoid counteracting C2 optimizations done | |
75 // on string literals), then they also become deduplication candidates if they reach | |
76 // the deduplication age threshold or are evacuated to an old heap region. The second | |
77 // attempt to deduplicate such strings will be in vain, but we have no fast way of | |
78 // filtering them out. This has not shown to be a problem, as the number of interned | |
79 // strings is usually dwarfed by the number of normal (non-interned) strings. | |
80 // | |
81 // For additional information on string deduplication, please see JEP 192, | |
82 // http://openjdk.java.net/jeps/192 | |
83 // | |
84 | |
85 #include "memory/allocation.hpp" | |
86 #include "oops/oop.hpp" | |
87 | |
88 class OopClosure; | |
89 class BoolObjectClosure; | |
90 class ThreadClosure; | |
91 class outputStream; | |
92 class G1StringDedupTable; | |
93 | |
94 // | |
95 // Main interface for interacting with string deduplication. | |
96 // | |
97 class G1StringDedup : public AllStatic { | |
98 private: | |
99 // Single state for checking if both G1 and string deduplication is enabled. | |
100 static bool _enabled; | |
101 | |
102 // Candidate selection policies, returns true if the given object is | |
103 // candidate for string deduplication. | |
104 static bool is_candidate_from_mark(oop obj); | |
105 static bool is_candidate_from_evacuation(bool from_young, bool to_young, oop obj); | |
106 | |
107 public: | |
108 // Returns true if both G1 and string deduplication is enabled. | |
109 static bool is_enabled() { | |
110 return _enabled; | |
111 } | |
112 | |
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113 // Initialize string deduplication. |
17764 | 114 static void initialize(); |
115 | |
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116 // Stop the deduplication thread. |
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117 static void stop(); |
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118 |
17764 | 119 // Immediately deduplicates the given String object, bypassing the |
120 // the deduplication queue. | |
121 static void deduplicate(oop java_string); | |
122 | |
123 // Enqueues a deduplication candidate for later processing by the deduplication | |
124 // thread. Before enqueuing, these functions apply the appropriate candidate | |
125 // selection policy to filters out non-candidates. | |
126 static void enqueue_from_mark(oop java_string); | |
127 static void enqueue_from_evacuation(bool from_young, bool to_young, | |
128 unsigned int queue, oop java_string); | |
129 | |
130 static void oops_do(OopClosure* keep_alive); | |
131 static void unlink(BoolObjectClosure* is_alive); | |
132 static void unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* keep_alive, | |
133 bool allow_resize_and_rehash = true); | |
134 | |
135 static void threads_do(ThreadClosure* tc); | |
136 static void print_worker_threads_on(outputStream* st); | |
137 static void verify(); | |
138 }; | |
139 | |
140 // | |
141 // This closure encapsulates the state and the closures needed when scanning | |
142 // the deduplication queue and table during the unlink_or_oops_do() operation. | |
143 // A single instance of this closure is created and then shared by all worker | |
144 // threads participating in the scan. The _next_queue and _next_bucket fields | |
145 // provide a simple mechanism for GC workers to claim exclusive access to a | |
146 // queue or a table partition. | |
147 // | |
148 class G1StringDedupUnlinkOrOopsDoClosure : public StackObj { | |
149 private: | |
150 BoolObjectClosure* _is_alive; | |
151 OopClosure* _keep_alive; | |
152 G1StringDedupTable* _resized_table; | |
153 G1StringDedupTable* _rehashed_table; | |
154 size_t _next_queue; | |
155 size_t _next_bucket; | |
156 | |
157 public: | |
158 G1StringDedupUnlinkOrOopsDoClosure(BoolObjectClosure* is_alive, | |
159 OopClosure* keep_alive, | |
160 bool allow_resize_and_rehash); | |
161 ~G1StringDedupUnlinkOrOopsDoClosure(); | |
162 | |
163 bool is_resizing() { | |
164 return _resized_table != NULL; | |
165 } | |
166 | |
167 G1StringDedupTable* resized_table() { | |
168 return _resized_table; | |
169 } | |
170 | |
171 bool is_rehashing() { | |
172 return _rehashed_table != NULL; | |
173 } | |
174 | |
175 // Atomically claims the next available queue for exclusive access by | |
176 // the current thread. Returns the queue number of the claimed queue. | |
177 size_t claim_queue() { | |
178 return (size_t)Atomic::add_ptr(1, &_next_queue) - 1; | |
179 } | |
180 | |
181 // Atomically claims the next available table partition for exclusive | |
182 // access by the current thread. Returns the table bucket number where | |
183 // the claimed partition starts. | |
184 size_t claim_table_partition(size_t partition_size) { | |
185 return (size_t)Atomic::add_ptr(partition_size, &_next_bucket) - partition_size; | |
186 } | |
187 | |
188 // Applies and returns the result from the is_alive closure, or | |
189 // returns true if no such closure was provided. | |
190 bool is_alive(oop o) { | |
191 if (_is_alive != NULL) { | |
192 return _is_alive->do_object_b(o); | |
193 } | |
194 return true; | |
195 } | |
196 | |
197 // Applies the keep_alive closure, or does nothing if no such | |
198 // closure was provided. | |
199 void keep_alive(oop* p) { | |
200 if (_keep_alive != NULL) { | |
201 _keep_alive->do_oop(p); | |
202 } | |
203 } | |
204 }; | |
205 | |
206 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP |