1 /*
   2  * Copyright (c) 2014, 2015, 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 #include "precompiled.hpp"
  26 #include "classfile/altHashing.hpp"
  27 #include "classfile/javaClasses.inline.hpp"
  28 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
  29 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
  30 #include "gc_implementation/g1/g1StringDedup.hpp"
  31 #include "gc_implementation/g1/g1StringDedupTable.hpp"
  32 #include "memory/gcLocker.hpp"
  33 #include "memory/padded.inline.hpp"
  34 #include "oops/typeArrayOop.hpp"
  35 #include "oops/oop.inline.hpp"
  36 #include "runtime/mutexLocker.hpp"
  37 
  38 //
  39 // Freelist in the deduplication table entry cache. Links table
  40 // entries together using their _next fields.
  41 //
  42 class G1StringDedupEntryFreeList : public CHeapObj<mtGC> {
  43 private:
  44   G1StringDedupEntry* _list;
  45   size_t              _length;
  46 
  47 public:
  48   G1StringDedupEntryFreeList() :
  49     _list(NULL),
  50     _length(0) {
  51   }
  52 
  53   void add(G1StringDedupEntry* entry) {
  54     entry->set_next(_list);
  55     _list = entry;
  56     _length++;
  57   }
  58 
  59   G1StringDedupEntry* remove() {
  60     G1StringDedupEntry* entry = _list;
  61     if (entry != NULL) {
  62       _list = entry->next();
  63       _length--;
  64     }
  65     return entry;
  66   }
  67 
  68   size_t length() {
  69     return _length;
  70   }
  71 };
  72 
  73 //
  74 // Cache of deduplication table entries. This cache provides fast allocation and
  75 // reuse of table entries to lower the pressure on the underlying allocator.
  76 // But more importantly, it provides fast/deferred freeing of table entries. This
  77 // is important because freeing of table entries is done during stop-the-world
  78 // phases and it is not uncommon for large number of entries to be freed at once.
  79 // Tables entries that are freed during these phases are placed onto a freelist in
  80 // the cache. The deduplication thread, which executes in a concurrent phase, will
  81 // later reuse or free the underlying memory for these entries.
  82 //
  83 // The cache allows for single-threaded allocations and multi-threaded frees.
  84 // Allocations are synchronized by StringDedupTable_lock as part of a table
  85 // modification.
  86 //
  87 class G1StringDedupEntryCache : public CHeapObj<mtGC> {
  88 private:
  89   // One freelist per GC worker to allow lock less freeing of
  90   // entries while doing a parallel scan of the table. Using
  91   // PaddedEnd to avoid false sharing.
  92   PaddedEnd<G1StringDedupEntryFreeList>* _lists;
  93   size_t                                 _nlists;
  94 
  95   // Never called.
  96   ~G1StringDedupEntryCache();
  97 
  98 public:
  99   G1StringDedupEntryCache();

 100 
 101   // Get a table entry from the cache freelist, or allocate a new
 102   // entry if the cache is empty.
 103   G1StringDedupEntry* alloc();
 104 
 105   // Insert a table entry into the cache freelist.
 106   void free(G1StringDedupEntry* entry, uint worker_id);
 107 
 108   // Returns current number of entries in the cache.
 109   size_t size();
 110 
 111   // If the cache has grown above the given max size, trim it down
 112   // and deallocate the memory occupied by trimmed of entries.
 113   void trim(size_t max_size);
 114 };
 115 
 116 G1StringDedupEntryCache::G1StringDedupEntryCache() {
 117   _nlists = MAX2(ParallelGCThreads, (size_t)1);
 118   _lists = PaddedArray<G1StringDedupEntryFreeList, mtGC>::create_unfreeable((uint)_nlists);




 119 }
 120 
 121 G1StringDedupEntry* G1StringDedupEntryCache::alloc() {
 122   for (size_t i = 0; i < _nlists; i++) {
 123     G1StringDedupEntry* entry = _lists[i].remove();
 124     if (entry != NULL) {
 125       return entry;
 126     }
 127   }
 128   return new G1StringDedupEntry();
 129 }
 130 
 131 void G1StringDedupEntryCache::free(G1StringDedupEntry* entry, uint worker_id) {
 132   assert(entry->obj() != NULL, "Double free");
 133   assert(worker_id < _nlists, "Invalid worker id");
 134   entry->set_obj(NULL);
 135   entry->set_hash(0);
 136   _lists[worker_id].add(entry);
 137 }
 138 
 139 size_t G1StringDedupEntryCache::size() {
 140   size_t size = 0;
 141   for (size_t i = 0; i < _nlists; i++) {
 142     size += _lists[i].length();
 143   }
 144   return size;
 145 }
 146 
 147 void G1StringDedupEntryCache::trim(size_t max_size) {
 148   size_t cache_size = 0;
 149   for (size_t i = 0; i < _nlists; i++) {
 150     G1StringDedupEntryFreeList* list = &_lists[i];
 151     cache_size += list->length();
 152     while (cache_size > max_size) {
 153       G1StringDedupEntry* entry = list->remove();
 154       assert(entry != NULL, "Should not be null");
 155       cache_size--;
 156       delete entry;
 157     }
 158   }
 159 }
 160 
 161 G1StringDedupTable*      G1StringDedupTable::_table = NULL;
 162 G1StringDedupEntryCache* G1StringDedupTable::_entry_cache = NULL;
 163 
 164 const size_t             G1StringDedupTable::_min_size = (1 << 10);   // 1024
 165 const size_t             G1StringDedupTable::_max_size = (1 << 24);   // 16777216
 166 const double             G1StringDedupTable::_grow_load_factor = 2.0; // Grow table at 200% load
 167 const double             G1StringDedupTable::_shrink_load_factor = _grow_load_factor / 3.0; // Shrink table at 67% load
 168 const double             G1StringDedupTable::_max_cache_factor = 0.1; // Cache a maximum of 10% of the table size
 169 const uintx              G1StringDedupTable::_rehash_multiple = 60;   // Hash bucket has 60 times more collisions than expected
 170 const uintx              G1StringDedupTable::_rehash_threshold = (uintx)(_rehash_multiple * _grow_load_factor);
 171 
 172 uintx                    G1StringDedupTable::_entries_added = 0;
 173 uintx                    G1StringDedupTable::_entries_removed = 0;
 174 uintx                    G1StringDedupTable::_resize_count = 0;
 175 uintx                    G1StringDedupTable::_rehash_count = 0;
 176 
 177 G1StringDedupTable::G1StringDedupTable(size_t size, jint hash_seed) :
 178   _size(size),
 179   _entries(0),
 180   _grow_threshold((uintx)(size * _grow_load_factor)),
 181   _shrink_threshold((uintx)(size * _shrink_load_factor)),
 182   _rehash_needed(false),
 183   _hash_seed(hash_seed) {
 184   assert(is_power_of_2(size), "Table size must be a power of 2");
 185   _buckets = NEW_C_HEAP_ARRAY(G1StringDedupEntry*, _size, mtGC);
 186   memset(_buckets, 0, _size * sizeof(G1StringDedupEntry*));
 187 }
 188 
 189 G1StringDedupTable::~G1StringDedupTable() {
 190   FREE_C_HEAP_ARRAY(G1StringDedupEntry*, _buckets);
 191 }
 192 
 193 void G1StringDedupTable::create() {
 194   assert(_table == NULL, "One string deduplication table allowed");
 195   _entry_cache = new G1StringDedupEntryCache();
 196   _table = new G1StringDedupTable(_min_size);
 197 }
 198 
 199 void G1StringDedupTable::add(typeArrayOop value, unsigned int hash, G1StringDedupEntry** list) {
 200   G1StringDedupEntry* entry = _entry_cache->alloc();
 201   entry->set_obj(value);
 202   entry->set_hash(hash);
 203   entry->set_next(*list);
 204   *list = entry;
 205   _entries++;
 206 }
 207 
 208 void G1StringDedupTable::remove(G1StringDedupEntry** pentry, uint worker_id) {
 209   G1StringDedupEntry* entry = *pentry;
 210   *pentry = entry->next();
 211   _entry_cache->free(entry, worker_id);
 212 }
 213 
 214 void G1StringDedupTable::transfer(G1StringDedupEntry** pentry, G1StringDedupTable* dest) {
 215   G1StringDedupEntry* entry = *pentry;
 216   *pentry = entry->next();
 217   unsigned int hash = entry->hash();
 218   size_t index = dest->hash_to_index(hash);
 219   G1StringDedupEntry** list = dest->bucket(index);
 220   entry->set_next(*list);
 221   *list = entry;
 222 }
 223 
 224 bool G1StringDedupTable::equals(typeArrayOop value1, typeArrayOop value2) {
 225   return (value1 == value2 ||
 226           (value1->length() == value2->length() &&
 227            (!memcmp(value1->base(T_CHAR),
 228                     value2->base(T_CHAR),
 229                     value1->length() * sizeof(jchar)))));
 230 }
 231 
 232 typeArrayOop G1StringDedupTable::lookup(typeArrayOop value, unsigned int hash,
 233                                         G1StringDedupEntry** list, uintx &count) {
 234   for (G1StringDedupEntry* entry = *list; entry != NULL; entry = entry->next()) {
 235     if (entry->hash() == hash) {
 236       typeArrayOop existing_value = entry->obj();
 237       if (equals(value, existing_value)) {
 238         // Match found
 239         return existing_value;
 240       }
 241     }
 242     count++;
 243   }
 244 
 245   // Not found
 246   return NULL;
 247 }
 248 
 249 typeArrayOop G1StringDedupTable::lookup_or_add_inner(typeArrayOop value, unsigned int hash) {
 250   size_t index = hash_to_index(hash);
 251   G1StringDedupEntry** list = bucket(index);
 252   uintx count = 0;
 253 
 254   // Lookup in list
 255   typeArrayOop existing_value = lookup(value, hash, list, count);
 256 
 257   // Check if rehash is needed
 258   if (count > _rehash_threshold) {
 259     _rehash_needed = true;
 260   }
 261 
 262   if (existing_value == NULL) {
 263     // Not found, add new entry
 264     add(value, hash, list);
 265 
 266     // Update statistics
 267     _entries_added++;
 268   }
 269 
 270   return existing_value;
 271 }
 272 
 273 unsigned int G1StringDedupTable::hash_code(typeArrayOop value) {
 274   unsigned int hash;
 275   int length = value->length();
 276   const jchar* data = (jchar*)value->base(T_CHAR);
 277 
 278   if (use_java_hash()) {
 279     hash = java_lang_String::hash_code(data, length);
 280   } else {
 281     hash = AltHashing::murmur3_32(_table->_hash_seed, data, length);
 282   }
 283 
 284   return hash;
 285 }
 286 
 287 void G1StringDedupTable::deduplicate(oop java_string, G1StringDedupStat& stat) {
 288   assert(java_lang_String::is_instance(java_string), "Must be a string");
 289   No_Safepoint_Verifier nsv;
 290 
 291   stat.inc_inspected();
 292 
 293   typeArrayOop value = java_lang_String::value(java_string);
 294   if (value == NULL) {
 295     // String has no value
 296     stat.inc_skipped();
 297     return;
 298   }
 299 
 300   unsigned int hash = 0;
 301 
 302   if (use_java_hash()) {
 303     // Get hash code from cache
 304     hash = java_lang_String::hash(java_string);
 305   }
 306 
 307   if (hash == 0) {
 308     // Compute hash
 309     hash = hash_code(value);
 310     stat.inc_hashed();
 311   }
 312 
 313   if (use_java_hash() && hash != 0) {
 314     // Store hash code in cache
 315     java_lang_String::set_hash(java_string, hash);
 316   }
 317 
 318   typeArrayOop existing_value = lookup_or_add(value, hash);
 319   if (existing_value == value) {
 320     // Same value, already known
 321     stat.inc_known();
 322     return;
 323   }
 324 
 325   // Get size of value array
 326   uintx size_in_bytes = value->size() * HeapWordSize;
 327   stat.inc_new(size_in_bytes);
 328 
 329   if (existing_value != NULL) {
 330     // Enqueue the reference to make sure it is kept alive. Concurrent mark might
 331     // otherwise declare it dead if there are no other strong references to this object.
 332     G1SATBCardTableModRefBS::enqueue(existing_value);
 333 
 334     // Existing value found, deduplicate string
 335     java_lang_String::set_value(java_string, existing_value);
 336 
 337     if (G1CollectedHeap::heap()->is_in_young(value)) {
 338       stat.inc_deduped_young(size_in_bytes);
 339     } else {
 340       stat.inc_deduped_old(size_in_bytes);
 341     }
 342   }
 343 }
 344 
 345 G1StringDedupTable* G1StringDedupTable::prepare_resize() {
 346   size_t size = _table->_size;
 347 
 348   // Check if the hashtable needs to be resized
 349   if (_table->_entries > _table->_grow_threshold) {
 350     // Grow table, double the size
 351     size *= 2;
 352     if (size > _max_size) {
 353       // Too big, don't resize
 354       return NULL;
 355     }
 356   } else if (_table->_entries < _table->_shrink_threshold) {
 357     // Shrink table, half the size
 358     size /= 2;
 359     if (size < _min_size) {
 360       // Too small, don't resize
 361       return NULL;
 362     }
 363   } else if (StringDeduplicationResizeALot) {
 364     // Force grow
 365     size *= 2;
 366     if (size > _max_size) {
 367       // Too big, force shrink instead
 368       size /= 4;
 369     }
 370   } else {
 371     // Resize not needed
 372     return NULL;
 373   }
 374 
 375   // Update statistics
 376   _resize_count++;
 377 
 378   // Allocate the new table. The new table will be populated by workers
 379   // calling unlink_or_oops_do() and finally installed by finish_resize().
 380   return new G1StringDedupTable(size, _table->_hash_seed);
 381 }
 382 
 383 void G1StringDedupTable::finish_resize(G1StringDedupTable* resized_table) {
 384   assert(resized_table != NULL, "Invalid table");
 385 
 386   resized_table->_entries = _table->_entries;
 387 
 388   // Free old table
 389   delete _table;
 390 
 391   // Install new table
 392   _table = resized_table;
 393 }
 394 
 395 void G1StringDedupTable::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, uint worker_id) {
 396   // The table is divided into partitions to allow lock-less parallel processing by
 397   // multiple worker threads. A worker thread first claims a partition, which ensures
 398   // exclusive access to that part of the table, then continues to process it. To allow
 399   // shrinking of the table in parallel we also need to make sure that the same worker
 400   // thread processes all partitions where entries will hash to the same destination
 401   // partition. Since the table size is always a power of two and we always shrink by
 402   // dividing the table in half, we know that for a given partition there is only one
 403   // other partition whoes entries will hash to the same destination partition. That
 404   // other partition is always the sibling partition in the second half of the table.
 405   // For example, if the table is divided into 8 partitions, the sibling of partition 0
 406   // is partition 4, the sibling of partition 1 is partition 5, etc.
 407   size_t table_half = _table->_size / 2;
 408 
 409   // Let each partition be one page worth of buckets
 410   size_t partition_size = MIN2(table_half, os::vm_page_size() / sizeof(G1StringDedupEntry*));
 411   assert(table_half % partition_size == 0, "Invalid partition size");
 412 
 413   // Number of entries removed during the scan
 414   uintx removed = 0;
 415 
 416   for (;;) {
 417     // Grab next partition to scan
 418     size_t partition_begin = cl->claim_table_partition(partition_size);
 419     size_t partition_end = partition_begin + partition_size;
 420     if (partition_begin >= table_half) {
 421       // End of table
 422       break;
 423     }
 424 
 425     // Scan the partition followed by the sibling partition in the second half of the table
 426     removed += unlink_or_oops_do(cl, partition_begin, partition_end, worker_id);
 427     removed += unlink_or_oops_do(cl, table_half + partition_begin, table_half + partition_end, worker_id);
 428   }
 429 
 430   // Delayed update avoid contention on the table lock
 431   if (removed > 0) {
 432     MutexLockerEx ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag);
 433     _table->_entries -= removed;
 434     _entries_removed += removed;
 435   }
 436 }
 437 
 438 uintx G1StringDedupTable::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl,
 439                                             size_t partition_begin,
 440                                             size_t partition_end,
 441                                             uint worker_id) {
 442   uintx removed = 0;
 443   for (size_t bucket = partition_begin; bucket < partition_end; bucket++) {
 444     G1StringDedupEntry** entry = _table->bucket(bucket);
 445     while (*entry != NULL) {
 446       oop* p = (oop*)(*entry)->obj_addr();
 447       if (cl->is_alive(*p)) {
 448         cl->keep_alive(p);
 449         if (cl->is_resizing()) {
 450           // We are resizing the table, transfer entry to the new table
 451           _table->transfer(entry, cl->resized_table());
 452         } else {
 453           if (cl->is_rehashing()) {
 454             // We are rehashing the table, rehash the entry but keep it
 455             // in the table. We can't transfer entries into the new table
 456             // at this point since we don't have exclusive access to all
 457             // destination partitions. finish_rehash() will do a single
 458             // threaded transfer of all entries.
 459             typeArrayOop value = (typeArrayOop)*p;
 460             unsigned int hash = hash_code(value);
 461             (*entry)->set_hash(hash);
 462           }
 463 
 464           // Move to next entry
 465           entry = (*entry)->next_addr();
 466         }
 467       } else {
 468         // Not alive, remove entry from table
 469         _table->remove(entry, worker_id);
 470         removed++;
 471       }
 472     }
 473   }
 474 
 475   return removed;
 476 }
 477 
 478 G1StringDedupTable* G1StringDedupTable::prepare_rehash() {
 479   if (!_table->_rehash_needed && !StringDeduplicationRehashALot) {
 480     // Rehash not needed
 481     return NULL;
 482   }
 483 
 484   // Update statistics
 485   _rehash_count++;
 486 
 487   // Compute new hash seed
 488   _table->_hash_seed = AltHashing::compute_seed();
 489 
 490   // Allocate the new table, same size and hash seed
 491   return new G1StringDedupTable(_table->_size, _table->_hash_seed);
 492 }
 493 
 494 void G1StringDedupTable::finish_rehash(G1StringDedupTable* rehashed_table) {
 495   assert(rehashed_table != NULL, "Invalid table");
 496 
 497   // Move all newly rehashed entries into the correct buckets in the new table
 498   for (size_t bucket = 0; bucket < _table->_size; bucket++) {
 499     G1StringDedupEntry** entry = _table->bucket(bucket);
 500     while (*entry != NULL) {
 501       _table->transfer(entry, rehashed_table);
 502     }
 503   }
 504 
 505   rehashed_table->_entries = _table->_entries;
 506 
 507   // Free old table
 508   delete _table;
 509 
 510   // Install new table
 511   _table = rehashed_table;
 512 }
 513 
 514 void G1StringDedupTable::verify() {
 515   for (size_t bucket = 0; bucket < _table->_size; bucket++) {
 516     // Verify entries
 517     G1StringDedupEntry** entry = _table->bucket(bucket);
 518     while (*entry != NULL) {
 519       typeArrayOop value = (*entry)->obj();
 520       guarantee(value != NULL, "Object must not be NULL");
 521       guarantee(G1CollectedHeap::heap()->is_in_reserved(value), "Object must be on the heap");
 522       guarantee(!value->is_forwarded(), "Object must not be forwarded");
 523       guarantee(value->is_typeArray(), "Object must be a typeArrayOop");
 524       unsigned int hash = hash_code(value);
 525       guarantee((*entry)->hash() == hash, "Table entry has inorrect hash");
 526       guarantee(_table->hash_to_index(hash) == bucket, "Table entry has incorrect index");
 527       entry = (*entry)->next_addr();
 528     }
 529 
 530     // Verify that we do not have entries with identical oops or identical arrays.
 531     // We only need to compare entries in the same bucket. If the same oop or an
 532     // identical array has been inserted more than once into different/incorrect
 533     // buckets the verification step above will catch that.
 534     G1StringDedupEntry** entry1 = _table->bucket(bucket);
 535     while (*entry1 != NULL) {
 536       typeArrayOop value1 = (*entry1)->obj();
 537       G1StringDedupEntry** entry2 = (*entry1)->next_addr();
 538       while (*entry2 != NULL) {
 539         typeArrayOop value2 = (*entry2)->obj();
 540         guarantee(!equals(value1, value2), "Table entries must not have identical arrays");
 541         entry2 = (*entry2)->next_addr();
 542       }
 543       entry1 = (*entry1)->next_addr();
 544     }
 545   }
 546 }
 547 
 548 void G1StringDedupTable::trim_entry_cache() {
 549   MutexLockerEx ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag);
 550   size_t max_cache_size = (size_t)(_table->_size * _max_cache_factor);
 551   _entry_cache->trim(max_cache_size);
 552 }
 553 
 554 void G1StringDedupTable::print_statistics(outputStream* st) {
 555   st->print_cr(
 556     "   [Table]\n"
 557     "      [Memory Usage: "G1_STRDEDUP_BYTES_FORMAT_NS"]\n"
 558     "      [Size: "SIZE_FORMAT", Min: "SIZE_FORMAT", Max: "SIZE_FORMAT"]\n"
 559     "      [Entries: "UINTX_FORMAT", Load: "G1_STRDEDUP_PERCENT_FORMAT_NS", Cached: " UINTX_FORMAT ", Added: "UINTX_FORMAT", Removed: "UINTX_FORMAT"]\n"
 560     "      [Resize Count: "UINTX_FORMAT", Shrink Threshold: "UINTX_FORMAT"("G1_STRDEDUP_PERCENT_FORMAT_NS"), Grow Threshold: "UINTX_FORMAT"("G1_STRDEDUP_PERCENT_FORMAT_NS")]\n"
 561     "      [Rehash Count: "UINTX_FORMAT", Rehash Threshold: "UINTX_FORMAT", Hash Seed: 0x%x]\n"
 562     "      [Age Threshold: "UINTX_FORMAT"]",
 563     G1_STRDEDUP_BYTES_PARAM(_table->_size * sizeof(G1StringDedupEntry*) + (_table->_entries + _entry_cache->size()) * sizeof(G1StringDedupEntry)),
 564     _table->_size, _min_size, _max_size,
 565     _table->_entries, (double)_table->_entries / (double)_table->_size * 100.0, _entry_cache->size(), _entries_added, _entries_removed,
 566     _resize_count, _table->_shrink_threshold, _shrink_load_factor * 100.0, _table->_grow_threshold, _grow_load_factor * 100.0,
 567     _rehash_count, _rehash_threshold, _table->_hash_seed,
 568     StringDeduplicationAgeThreshold);
 569 }
--- EOF ---