Mercurial > hg > graal-compiler
view src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp @ 20280:bac98749fe00
8049831: Metadata Full GCs are not triggered when CMSClassUnloadingEnabled is turned off
Reviewed-by: brutisso, tschatzl, ehelin, jmasa, dfazunen
author | stefank |
---|---|
date | Fri, 11 Jul 2014 09:07:23 +0200 |
parents | 595c0f60d50d |
children |
line wrap: on
line source
/* * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPTABLE_HPP #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPTABLE_HPP #include "gc_implementation/g1/g1StringDedupStat.hpp" #include "runtime/mutexLocker.hpp" class G1StringDedupEntryCache; // // Table entry in the deduplication hashtable. Points weakly to the // character array. Can be chained in a linked list in case of hash // collisions or when placed in a freelist in the entry cache. // class G1StringDedupEntry : public CHeapObj<mtGC> { private: G1StringDedupEntry* _next; unsigned int _hash; typeArrayOop _obj; public: G1StringDedupEntry() : _next(NULL), _hash(0), _obj(NULL) { } G1StringDedupEntry* next() { return _next; } G1StringDedupEntry** next_addr() { return &_next; } void set_next(G1StringDedupEntry* next) { _next = next; } unsigned int hash() { return _hash; } void set_hash(unsigned int hash) { _hash = hash; } typeArrayOop obj() { return _obj; } typeArrayOop* obj_addr() { return &_obj; } void set_obj(typeArrayOop obj) { _obj = obj; } }; // // The deduplication hashtable keeps track of all unique character arrays used // by String objects. Each table entry weakly points to an character array, allowing // otherwise unreachable character arrays to be declared dead and pruned from the // table. // // The table is dynamically resized to accommodate the current number of table entries. // The table has hash buckets with chains for hash collision. If the average chain // length goes above or below given thresholds the table grows or shrinks accordingly. // // The table is also dynamically rehashed (using a new hash seed) if it becomes severely // unbalanced, i.e., a hash chain is significantly longer than average. // // All access to the table is protected by the StringDedupTable_lock, except under // safepoints in which case GC workers are allowed to access a table partitions they // have claimed without first acquiring the lock. Note however, that this applies only // the table partition (i.e. a range of elements in _buckets), not other parts of the // table such as the _entries field, statistics counters, etc. // class G1StringDedupTable : public CHeapObj<mtGC> { private: // The currently active hashtable instance. Only modified when // the table is resizes or rehashed. static G1StringDedupTable* _table; // Cache for reuse and fast alloc/free of table entries. static G1StringDedupEntryCache* _entry_cache; G1StringDedupEntry** _buckets; size_t _size; uintx _entries; uintx _shrink_threshold; uintx _grow_threshold; bool _rehash_needed; // The hash seed also dictates which hash function to use. A // zero hash seed means we will use the Java compatible hash // function (which doesn't use a seed), and a non-zero hash // seed means we use the murmur3 hash function. jint _hash_seed; // Constants governing table resize/rehash/cache. static const size_t _min_size; static const size_t _max_size; static const double _grow_load_factor; static const double _shrink_load_factor; static const uintx _rehash_multiple; static const uintx _rehash_threshold; static const double _max_cache_factor; // Table statistics, only used for logging. static uintx _entries_added; static uintx _entries_removed; static uintx _resize_count; static uintx _rehash_count; G1StringDedupTable(size_t size, jint hash_seed = 0); ~G1StringDedupTable(); // Returns the hash bucket at the given index. G1StringDedupEntry** bucket(size_t index) { return _buckets + index; } // Returns the hash bucket index for the given hash code. size_t hash_to_index(unsigned int hash) { return (size_t)hash & (_size - 1); } // Adds a new table entry to the given hash bucket. void add(typeArrayOop value, unsigned int hash, G1StringDedupEntry** list); // Removes the given table entry from the table. void remove(G1StringDedupEntry** pentry, uint worker_id); // Transfers a table entry from the current table to the destination table. void transfer(G1StringDedupEntry** pentry, G1StringDedupTable* dest); // Returns an existing character array in the given hash bucket, or NULL // if no matching character array exists. typeArrayOop lookup(typeArrayOop value, unsigned int hash, G1StringDedupEntry** list, uintx &count); // Returns an existing character array in the table, or inserts a new // table entry if no matching character array exists. typeArrayOop lookup_or_add_inner(typeArrayOop value, unsigned int hash); // Thread safe lookup or add of table entry static typeArrayOop lookup_or_add(typeArrayOop value, unsigned int hash) { // Protect the table from concurrent access. Also note that this lock // acts as a fence for _table, which could have been replaced by a new // instance if the table was resized or rehashed. MutexLockerEx ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag); return _table->lookup_or_add_inner(value, hash); } // Returns true if the hashtable is currently using a Java compatible // hash function. static bool use_java_hash() { return _table->_hash_seed == 0; } static bool equals(typeArrayOop value1, typeArrayOop value2); // Computes the hash code for the given character array, using the // currently active hash function and hash seed. static unsigned int hash_code(typeArrayOop value); static uintx unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t partition_begin, size_t partition_end, uint worker_id); public: static void create(); // Deduplicates the given String object, or adds its backing // character array to the deduplication hashtable. static void deduplicate(oop java_string, G1StringDedupStat& stat); // If a table resize is needed, returns a newly allocated empty // hashtable of the proper size. static G1StringDedupTable* prepare_resize(); // Installs a newly resized table as the currently active table // and deletes the previously active table. static void finish_resize(G1StringDedupTable* resized_table); // If a table rehash is needed, returns a newly allocated empty // hashtable and updates the hash seed. static G1StringDedupTable* prepare_rehash(); // Transfers rehashed entries from the currently active table into // the new table. Installs the new table as the currently active table // and deletes the previously active table. static void finish_rehash(G1StringDedupTable* rehashed_table); // If the table entry cache has grown too large, trim it down according to policy static void trim_entry_cache(); static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, uint worker_id); static void print_statistics(outputStream* st); static void verify(); }; #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPTABLE_HPP