jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp@595c0f60d50d (annotated)

src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp@595c0f60d50d (annotated)

src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp

Tue, 18 Mar 2014 19:07:22 +0100

author: pliden
date: Tue, 18 Mar 2014 19:07:22 +0100
changeset 6413: 595c0f60d50d
parent 0: f90c822e73f8
child 8452: 04a62a3d51d7
permissions: -rw-r--r--

8029075: String deduplication in G1
Summary: Implementation of JEP 192, http://openjdk.java.net/jeps/192
Reviewed-by: brutisso, tschatzl, coleenp

 /*
  * 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

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp@595c0f60d50d (annotated)

src/share/vm/gc_implementation/g1/g1StringDedupTable.hpp