Mercurial > hg > truffle
annotate src/share/vm/gc_implementation/g1/g1StringDedup.hpp @ 20190:0982ec23da03
8043607: Add a GC id as a log decoration similar to PrintGCTimeStamps
Reviewed-by: jwilhelm, ehelin, tschatzl
| author | brutisso |
|---|---|
| date | Thu, 19 Jun 2014 13:31:14 +0200 |
| parents | 1772223a25a2 |
| children |
| 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 |