Thu, 21 Aug 2014 16:44:41 +0200
8055098: WB API should be extended to provide information about size and age of object.
Summary: Extend the WhiteBox API to provide information about the size and age of objects. Further add a mechanism to trigger a young GC.
Reviewed-by: tschatzl, sjohanss
Contributed-by: Leonid Mesnik <leonid.mesnik@oracle.com>
pliden@6413 | 1 | /* |
pliden@6413 | 2 | * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. |
pliden@6413 | 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
pliden@6413 | 4 | * |
pliden@6413 | 5 | * This code is free software; you can redistribute it and/or modify it |
pliden@6413 | 6 | * under the terms of the GNU General Public License version 2 only, as |
pliden@6413 | 7 | * published by the Free Software Foundation. |
pliden@6413 | 8 | * |
pliden@6413 | 9 | * This code is distributed in the hope that it will be useful, but WITHOUT |
pliden@6413 | 10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
pliden@6413 | 11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
pliden@6413 | 12 | * version 2 for more details (a copy is included in the LICENSE file that |
pliden@6413 | 13 | * accompanied this code). |
pliden@6413 | 14 | * |
pliden@6413 | 15 | * You should have received a copy of the GNU General Public License version |
pliden@6413 | 16 | * 2 along with this work; if not, write to the Free Software Foundation, |
pliden@6413 | 17 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
pliden@6413 | 18 | * |
pliden@6413 | 19 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
pliden@6413 | 20 | * or visit www.oracle.com if you need additional information or have any |
pliden@6413 | 21 | * questions. |
pliden@6413 | 22 | * |
pliden@6413 | 23 | */ |
pliden@6413 | 24 | |
pliden@6413 | 25 | #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP |
pliden@6413 | 26 | #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP |
pliden@6413 | 27 | |
pliden@6413 | 28 | // |
pliden@6413 | 29 | // String Deduplication |
pliden@6413 | 30 | // |
pliden@6413 | 31 | // String deduplication aims to reduce the heap live-set by deduplicating identical |
pliden@6413 | 32 | // instances of String so that they share the same backing character array. |
pliden@6413 | 33 | // |
pliden@6413 | 34 | // The deduplication process is divided in two main parts, 1) finding the objects to |
pliden@6413 | 35 | // deduplicate, and 2) deduplicating those objects. The first part is done as part of |
pliden@6413 | 36 | // a normal GC cycle when objects are marked or evacuated. At this time a check is |
pliden@6413 | 37 | // applied on each object to check if it is a candidate for deduplication. If so, the |
pliden@6413 | 38 | // object is placed on the deduplication queue for later processing. The second part, |
pliden@6413 | 39 | // processing the objects on the deduplication queue, is a concurrent phase which |
pliden@6413 | 40 | // starts right after the stop-the-wold marking/evacuation phase. This phase is |
pliden@6413 | 41 | // executed by the deduplication thread, which pulls deduplication candidates of the |
pliden@6413 | 42 | // deduplication queue and tries to deduplicate them. |
pliden@6413 | 43 | // |
pliden@6413 | 44 | // A deduplication hashtable is used to keep track of all unique character arrays |
pliden@6413 | 45 | // used by String objects. When deduplicating, a lookup is made in this table to see |
pliden@6413 | 46 | // if there is already an identical character array somewhere on the heap. If so, the |
pliden@6413 | 47 | // String object is adjusted to point to that character array, releasing the reference |
pliden@6413 | 48 | // to the original array allowing it to eventually be garbage collected. If the lookup |
pliden@6413 | 49 | // fails the character array is instead inserted into the hashtable so that this array |
pliden@6413 | 50 | // can be shared at some point in the future. |
pliden@6413 | 51 | // |
pliden@6413 | 52 | // Candidate selection |
pliden@6413 | 53 | // |
pliden@6413 | 54 | // An object is considered a deduplication candidate if all of the following |
pliden@6413 | 55 | // statements are true: |
pliden@6413 | 56 | // |
pliden@6413 | 57 | // - The object is an instance of java.lang.String |
pliden@6413 | 58 | // |
pliden@6413 | 59 | // - The object is being evacuated from a young heap region |
pliden@6413 | 60 | // |
pliden@6413 | 61 | // - The object is being evacuated to a young/survivor heap region and the |
pliden@6413 | 62 | // object's age is equal to the deduplication age threshold |
pliden@6413 | 63 | // |
pliden@6413 | 64 | // or |
pliden@6413 | 65 | // |
pliden@6413 | 66 | // The object is being evacuated to an old heap region and the object's age is |
pliden@6413 | 67 | // less than the deduplication age threshold |
pliden@6413 | 68 | // |
pliden@6413 | 69 | // Once an string object has been promoted to an old region, or its age is higher |
pliden@6413 | 70 | // than the deduplication age threshold, is will never become a candidate again. |
pliden@6413 | 71 | // This approach avoids making the same object a candidate more than once. |
pliden@6413 | 72 | // |
pliden@6413 | 73 | // Interned strings are a bit special. They are explicitly deduplicated just before |
pliden@6413 | 74 | // being inserted into the StringTable (to avoid counteracting C2 optimizations done |
pliden@6413 | 75 | // on string literals), then they also become deduplication candidates if they reach |
pliden@6413 | 76 | // the deduplication age threshold or are evacuated to an old heap region. The second |
pliden@6413 | 77 | // attempt to deduplicate such strings will be in vain, but we have no fast way of |
pliden@6413 | 78 | // filtering them out. This has not shown to be a problem, as the number of interned |
pliden@6413 | 79 | // strings is usually dwarfed by the number of normal (non-interned) strings. |
pliden@6413 | 80 | // |
pliden@6413 | 81 | // For additional information on string deduplication, please see JEP 192, |
pliden@6413 | 82 | // http://openjdk.java.net/jeps/192 |
pliden@6413 | 83 | // |
pliden@6413 | 84 | |
pliden@6413 | 85 | #include "memory/allocation.hpp" |
pliden@6413 | 86 | #include "oops/oop.hpp" |
pliden@6413 | 87 | |
pliden@6413 | 88 | class OopClosure; |
pliden@6413 | 89 | class BoolObjectClosure; |
pliden@6413 | 90 | class ThreadClosure; |
pliden@6413 | 91 | class outputStream; |
pliden@6413 | 92 | class G1StringDedupTable; |
pliden@6413 | 93 | |
pliden@6413 | 94 | // |
pliden@6413 | 95 | // Main interface for interacting with string deduplication. |
pliden@6413 | 96 | // |
pliden@6413 | 97 | class G1StringDedup : public AllStatic { |
pliden@6413 | 98 | private: |
pliden@6413 | 99 | // Single state for checking if both G1 and string deduplication is enabled. |
pliden@6413 | 100 | static bool _enabled; |
pliden@6413 | 101 | |
pliden@6413 | 102 | // Candidate selection policies, returns true if the given object is |
pliden@6413 | 103 | // candidate for string deduplication. |
pliden@6413 | 104 | static bool is_candidate_from_mark(oop obj); |
pliden@6413 | 105 | static bool is_candidate_from_evacuation(bool from_young, bool to_young, oop obj); |
pliden@6413 | 106 | |
pliden@6413 | 107 | public: |
pliden@6413 | 108 | // Returns true if both G1 and string deduplication is enabled. |
pliden@6413 | 109 | static bool is_enabled() { |
pliden@6413 | 110 | return _enabled; |
pliden@6413 | 111 | } |
pliden@6413 | 112 | |
pliden@6690 | 113 | // Initialize string deduplication. |
pliden@6413 | 114 | static void initialize(); |
pliden@6413 | 115 | |
pliden@6690 | 116 | // Stop the deduplication thread. |
pliden@6690 | 117 | static void stop(); |
pliden@6690 | 118 | |
pliden@6413 | 119 | // Immediately deduplicates the given String object, bypassing the |
pliden@6413 | 120 | // the deduplication queue. |
pliden@6413 | 121 | static void deduplicate(oop java_string); |
pliden@6413 | 122 | |
pliden@6413 | 123 | // Enqueues a deduplication candidate for later processing by the deduplication |
pliden@6413 | 124 | // thread. Before enqueuing, these functions apply the appropriate candidate |
pliden@6413 | 125 | // selection policy to filters out non-candidates. |
pliden@6413 | 126 | static void enqueue_from_mark(oop java_string); |
pliden@6413 | 127 | static void enqueue_from_evacuation(bool from_young, bool to_young, |
pliden@6413 | 128 | unsigned int queue, oop java_string); |
pliden@6413 | 129 | |
pliden@6413 | 130 | static void oops_do(OopClosure* keep_alive); |
pliden@6413 | 131 | static void unlink(BoolObjectClosure* is_alive); |
pliden@6413 | 132 | static void unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* keep_alive, |
pliden@6413 | 133 | bool allow_resize_and_rehash = true); |
pliden@6413 | 134 | |
pliden@6413 | 135 | static void threads_do(ThreadClosure* tc); |
pliden@6413 | 136 | static void print_worker_threads_on(outputStream* st); |
pliden@6413 | 137 | static void verify(); |
pliden@6413 | 138 | }; |
pliden@6413 | 139 | |
pliden@6413 | 140 | // |
pliden@6413 | 141 | // This closure encapsulates the state and the closures needed when scanning |
pliden@6413 | 142 | // the deduplication queue and table during the unlink_or_oops_do() operation. |
pliden@6413 | 143 | // A single instance of this closure is created and then shared by all worker |
pliden@6413 | 144 | // threads participating in the scan. The _next_queue and _next_bucket fields |
pliden@6413 | 145 | // provide a simple mechanism for GC workers to claim exclusive access to a |
pliden@6413 | 146 | // queue or a table partition. |
pliden@6413 | 147 | // |
pliden@6413 | 148 | class G1StringDedupUnlinkOrOopsDoClosure : public StackObj { |
pliden@6413 | 149 | private: |
pliden@6413 | 150 | BoolObjectClosure* _is_alive; |
pliden@6413 | 151 | OopClosure* _keep_alive; |
pliden@6413 | 152 | G1StringDedupTable* _resized_table; |
pliden@6413 | 153 | G1StringDedupTable* _rehashed_table; |
pliden@6413 | 154 | size_t _next_queue; |
pliden@6413 | 155 | size_t _next_bucket; |
pliden@6413 | 156 | |
pliden@6413 | 157 | public: |
pliden@6413 | 158 | G1StringDedupUnlinkOrOopsDoClosure(BoolObjectClosure* is_alive, |
pliden@6413 | 159 | OopClosure* keep_alive, |
pliden@6413 | 160 | bool allow_resize_and_rehash); |
pliden@6413 | 161 | ~G1StringDedupUnlinkOrOopsDoClosure(); |
pliden@6413 | 162 | |
pliden@6413 | 163 | bool is_resizing() { |
pliden@6413 | 164 | return _resized_table != NULL; |
pliden@6413 | 165 | } |
pliden@6413 | 166 | |
pliden@6413 | 167 | G1StringDedupTable* resized_table() { |
pliden@6413 | 168 | return _resized_table; |
pliden@6413 | 169 | } |
pliden@6413 | 170 | |
pliden@6413 | 171 | bool is_rehashing() { |
pliden@6413 | 172 | return _rehashed_table != NULL; |
pliden@6413 | 173 | } |
pliden@6413 | 174 | |
pliden@6413 | 175 | // Atomically claims the next available queue for exclusive access by |
pliden@6413 | 176 | // the current thread. Returns the queue number of the claimed queue. |
pliden@6413 | 177 | size_t claim_queue() { |
pliden@6413 | 178 | return (size_t)Atomic::add_ptr(1, &_next_queue) - 1; |
pliden@6413 | 179 | } |
pliden@6413 | 180 | |
pliden@6413 | 181 | // Atomically claims the next available table partition for exclusive |
pliden@6413 | 182 | // access by the current thread. Returns the table bucket number where |
pliden@6413 | 183 | // the claimed partition starts. |
pliden@6413 | 184 | size_t claim_table_partition(size_t partition_size) { |
pliden@6413 | 185 | return (size_t)Atomic::add_ptr(partition_size, &_next_bucket) - partition_size; |
pliden@6413 | 186 | } |
pliden@6413 | 187 | |
pliden@6413 | 188 | // Applies and returns the result from the is_alive closure, or |
pliden@6413 | 189 | // returns true if no such closure was provided. |
pliden@6413 | 190 | bool is_alive(oop o) { |
pliden@6413 | 191 | if (_is_alive != NULL) { |
pliden@6413 | 192 | return _is_alive->do_object_b(o); |
pliden@6413 | 193 | } |
pliden@6413 | 194 | return true; |
pliden@6413 | 195 | } |
pliden@6413 | 196 | |
pliden@6413 | 197 | // Applies the keep_alive closure, or does nothing if no such |
pliden@6413 | 198 | // closure was provided. |
pliden@6413 | 199 | void keep_alive(oop* p) { |
pliden@6413 | 200 | if (_keep_alive != NULL) { |
pliden@6413 | 201 | _keep_alive->do_oop(p); |
pliden@6413 | 202 | } |
pliden@6413 | 203 | } |
pliden@6413 | 204 | }; |
pliden@6413 | 205 | |
pliden@6413 | 206 | #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP |