jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/g1/g1StringDedupTable.cpp@fd3484fadbe3 (annotated)

src/share/vm/gc_implementation/g1/g1StringDedupTable.cpp@fd3484fadbe3 (annotated)

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

Wed, 23 Sep 2020 15:18:53 +0300

author: vkempik
date: Wed, 23 Sep 2020 15:18:53 +0300
changeset 10008: fd3484fadbe3
parent 9327: f96fcd9e1e1b
child 10009: 8adf45218add
permissions: -rw-r--r--

8240124: Better VM Interning
Reviewed-by: mbalao, andrew

 /*
  * Copyright (c) 2014, 2016, 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.
  *
  */
 #include "precompiled.hpp"
 #include "classfile/altHashing.hpp"
 #include "classfile/javaClasses.hpp"
 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
 #include "gc_implementation/g1/g1StringDedupTable.hpp"
 #include "gc_implementation/shared/concurrentGCThread.hpp"
 #include "memory/gcLocker.hpp"
 #include "memory/padded.inline.hpp"
 #include "oops/typeArrayOop.hpp"
 #include "runtime/mutexLocker.hpp"
 //
 // List of deduplication table entries. Links table
 // entries together using their _next fields.
 //
 class G1StringDedupEntryList : public CHeapObj<mtGC> {
 private:
   G1StringDedupEntry* _list;
   size_t              _length;
 public:
   G1StringDedupEntryList() :
     _list(NULL),
     _length(0) {
   }
   void add(G1StringDedupEntry* entry) {
     entry->set_next(_list);
     _list = entry;
     _length++;
   }
   G1StringDedupEntry* remove() {
     G1StringDedupEntry* entry = _list;
     if (entry != NULL) {
       _list = entry->next();
       _length--;
     }
     return entry;
   }
   G1StringDedupEntry* remove_all() {
     G1StringDedupEntry* list = _list;
     _list = NULL;
     return list;
   }
   size_t length() {
     return _length;
   }
 };
 //
 // Cache of deduplication table entries. This cache provides fast allocation and
 // reuse of table entries to lower the pressure on the underlying allocator.
 // But more importantly, it provides fast/deferred freeing of table entries. This
 // is important because freeing of table entries is done during stop-the-world
 // phases and it is not uncommon for large number of entries to be freed at once.
 // Tables entries that are freed during these phases are placed onto a freelist in
 // the cache. The deduplication thread, which executes in a concurrent phase, will
 // later reuse or free the underlying memory for these entries.
 //
 // The cache allows for single-threaded allocations and multi-threaded frees.
 // Allocations are synchronized by StringDedupTable_lock as part of a table
 // modification.
 //
 class G1StringDedupEntryCache : public CHeapObj<mtGC> {
 private:
   // One cache/overflow list per GC worker to allow lock less freeing of
   // entries while doing a parallel scan of the table. Using PaddedEnd to
   // avoid false sharing.
   size_t                             _nlists;
   size_t                             _max_list_length;
   PaddedEnd<G1StringDedupEntryList>* _cached;
   PaddedEnd<G1StringDedupEntryList>* _overflowed;
 public:
   G1StringDedupEntryCache(size_t max_size);
   ~G1StringDedupEntryCache();
   // Set max number of table entries to cache.
   void set_max_size(size_t max_size);
   // Get a table entry from the cache, or allocate a new entry if the cache is empty.
   G1StringDedupEntry* alloc();
   // Insert a table entry into the cache.
   void free(G1StringDedupEntry* entry, uint worker_id);
   // Returns current number of entries in the cache.
   size_t size();
   // Deletes overflowed entries.
   void delete_overflowed();
 };
 G1StringDedupEntryCache::G1StringDedupEntryCache(size_t max_size) :
   _nlists(MAX2(ParallelGCThreads, (size_t)1)),
   _max_list_length(0),
   _cached(PaddedArray<G1StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)),
   _overflowed(PaddedArray<G1StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)) {
   set_max_size(max_size);
 }
 G1StringDedupEntryCache::~G1StringDedupEntryCache() {
   ShouldNotReachHere();
 }
 void G1StringDedupEntryCache::set_max_size(size_t size) {
   _max_list_length = size / _nlists;
 }
 G1StringDedupEntry* G1StringDedupEntryCache::alloc() {
   for (size_t i = 0; i < _nlists; i++) {
     G1StringDedupEntry* entry = _cached[i].remove();
     if (entry != NULL) {
       return entry;
     }
   }
   return new G1StringDedupEntry();
 }
 void G1StringDedupEntryCache::free(G1StringDedupEntry* entry, uint worker_id) {
   assert(entry->obj() != NULL, "Double free");
   assert(worker_id < _nlists, "Invalid worker id");
   entry->set_obj(NULL);
   entry->set_java_hash(0);
   if (_cached[worker_id].length() < _max_list_length) {
     // Cache is not full
     _cached[worker_id].add(entry);
   } else {
     // Cache is full, add to overflow list for later deletion
     _overflowed[worker_id].add(entry);
   }
 }
 size_t G1StringDedupEntryCache::size() {
   size_t size = 0;
   for (size_t i = 0; i < _nlists; i++) {
     size += _cached[i].length();
   }
   return size;
 }
 void G1StringDedupEntryCache::delete_overflowed() {
   double start = os::elapsedTime();
   uintx count = 0;
   for (size_t i = 0; i < _nlists; i++) {
     G1StringDedupEntry* entry;
     {
       // The overflow list can be modified during safepoints, therefore
       // we temporarily join the suspendible thread set while removing
       // all entries from the list.
       SuspendibleThreadSetJoiner sts_join;
       entry = _overflowed[i].remove_all();
     }
     // Delete all entries
     while (entry != NULL) {
       G1StringDedupEntry* next = entry->next();
       delete entry;
       entry = next;
       count++;
     }
   }
   double end = os::elapsedTime();
   if (PrintStringDeduplicationStatistics) {
     gclog_or_tty->print_cr("[GC concurrent-string-deduplication, deleted " UINTX_FORMAT " entries, " G1_STRDEDUP_TIME_FORMAT "]", count, end - start);
   }
 }
 G1StringDedupTable*      G1StringDedupTable::_table = NULL;
 G1StringDedupEntryCache* G1StringDedupTable::_entry_cache = NULL;
 const size_t             G1StringDedupTable::_min_size = (1 << 10);   // 1024
 const size_t             G1StringDedupTable::_max_size = (1 << 24);   // 16777216
 const double             G1StringDedupTable::_grow_load_factor = 2.0; // Grow table at 200% load
 const double             G1StringDedupTable::_shrink_load_factor = _grow_load_factor / 3.0; // Shrink table at 67% load
 const double             G1StringDedupTable::_max_cache_factor = 0.1; // Cache a maximum of 10% of the table size
 const uintx              G1StringDedupTable::_rehash_multiple = 60;   // Hash bucket has 60 times more collisions than expected
 const uintx              G1StringDedupTable::_rehash_threshold = (uintx)(_rehash_multiple * _grow_load_factor);
 uintx                    G1StringDedupTable::_entries_added = 0;
 uintx                    G1StringDedupTable::_entries_removed = 0;
 uintx                    G1StringDedupTable::_resize_count = 0;
 uintx                    G1StringDedupTable::_rehash_count = 0;
 G1StringDedupTable::G1StringDedupTable(size_t size, uint64_t hash_seed) :
   _size(size),
   _entries(0),
   _grow_threshold((uintx)(size * _grow_load_factor)),
   _shrink_threshold((uintx)(size * _shrink_load_factor)),
   _rehash_needed(false),
   _hash_seed(hash_seed) {
   assert(is_power_of_2(size), "Table size must be a power of 2");
   _buckets = NEW_C_HEAP_ARRAY(G1StringDedupEntry*, _size, mtGC);
   memset(_buckets, 0, _size * sizeof(G1StringDedupEntry*));
 }
 G1StringDedupTable::~G1StringDedupTable() {
   FREE_C_HEAP_ARRAY(G1StringDedupEntry*, _buckets, mtGC);
 }
 void G1StringDedupTable::create() {
   assert(_table == NULL, "One string deduplication table allowed");
   _entry_cache = new G1StringDedupEntryCache((size_t)(_min_size * _max_cache_factor));
   _table = new G1StringDedupTable(_min_size);
 }
 void G1StringDedupTable::add(typeArrayOop value, uint64_t hash, G1StringDedupEntry** list) {
   G1StringDedupEntry* entry = _entry_cache->alloc();
   entry->set_obj(value);
   if (use_java_hash()) {
     entry->set_java_hash((unsigned int)hash);
   } else {
     entry->set_alt_hash(hash);
   }
   entry->set_next(*list);
   *list = entry;
   _entries++;
 }
 void G1StringDedupTable::remove(G1StringDedupEntry** pentry, uint worker_id) {
   G1StringDedupEntry* entry = *pentry;
   *pentry = entry->next();
   _entry_cache->free(entry, worker_id);
 }
 void G1StringDedupTable::transfer(G1StringDedupEntry** pentry, G1StringDedupTable* dest) {
   G1StringDedupEntry* entry = *pentry;
   *pentry = entry->next();
   uint64_t hash = use_java_hash() ? entry->java_hash() : entry->alt_hash();
   size_t index = dest->hash_to_index(hash);
   G1StringDedupEntry** list = dest->bucket(index);
   entry->set_next(*list);
   *list = entry;
 }
 bool G1StringDedupTable::equals(typeArrayOop value1, typeArrayOop value2) {
   return (value1 == value2 ||
           (value1->length() == value2->length() &&
            (!memcmp(value1->base(T_CHAR),
                     value2->base(T_CHAR),
                     value1->length() * sizeof(jchar)))));
 }
 typeArrayOop G1StringDedupTable::lookup(typeArrayOop value, uint64_t hash,
                                         G1StringDedupEntry** list, uintx &count) {
   for (G1StringDedupEntry* entry = *list; entry != NULL; entry = entry->next()) {
     if ((use_java_hash() ? entry->java_hash() : entry->alt_hash()) == hash) {
       typeArrayOop existing_value = entry->obj();
       if (equals(value, existing_value)) {
         // Match found
         return existing_value;
       }
     }
     count++;
   }
   // Not found
   return NULL;
 }
 typeArrayOop G1StringDedupTable::lookup_or_add_inner(typeArrayOop value, uint64_t hash) {
   size_t index = hash_to_index(hash);
   G1StringDedupEntry** list = bucket(index);
   uintx count = 0;
   // Lookup in list
   typeArrayOop existing_value = lookup(value, hash, list, count);
   // Check if rehash is needed
   if (count > _rehash_threshold) {
     _rehash_needed = true;
   }
   if (existing_value == NULL) {
     // Not found, add new entry
     add(value, hash, list);
     // Update statistics
     _entries_added++;
   }
   return existing_value;
 }
 unsigned int G1StringDedupTable::java_hash_code(typeArrayOop value) {
   assert(use_java_hash(), "Should not use java hash code");
   unsigned int hash;
   int length = value->length();
   const jchar* data = (jchar*)value->base(T_CHAR);
   hash = java_lang_String::hash_code(data, length);
   return hash;
 }
 uint64_t G1StringDedupTable::alt_hash_code(typeArrayOop value) {
   assert(!use_java_hash(), "Should not use alt hash code");
   int length = value->length();
   const jbyte* data = (jbyte*)value->base(T_BYTE);
   return AltHashing::halfsiphash_64(_table->_hash_seed, (const int8_t*)data, length);
 }
 void G1StringDedupTable::deduplicate(oop java_string, G1StringDedupStat& stat) {
   assert(java_lang_String::is_instance(java_string), "Must be a string");
   No_Safepoint_Verifier nsv;
   stat.inc_inspected();
   typeArrayOop value = java_lang_String::value(java_string);
   if (value == NULL) {
     // String has no value
     stat.inc_skipped();
     return;
   }
   uint64_t hash = 0;
   if (use_java_hash()) {
     // Get hash code from cache
     hash = java_lang_String::hash(java_string);
   }
   if (hash == 0) {
     // Compute hash
     hash = alt_hash_code(value);
     stat.inc_hashed();
   }
   if (use_java_hash() && hash != 0) {
     // Store hash code in cache
     java_lang_String::set_hash(java_string, hash);
   }
   typeArrayOop existing_value = lookup_or_add(value, hash);
   if (existing_value == value) {
     // Same value, already known
     stat.inc_known();
     return;
   }
   // Get size of value array
   uintx size_in_bytes = value->size() * HeapWordSize;
   stat.inc_new(size_in_bytes);
   if (existing_value != NULL) {
     // Enqueue the reference to make sure it is kept alive. Concurrent mark might
     // otherwise declare it dead if there are no other strong references to this object.
     G1SATBCardTableModRefBS::enqueue(existing_value);
     // Existing value found, deduplicate string
     java_lang_String::set_value(java_string, existing_value);
     if (G1CollectedHeap::heap()->is_in_young(value)) {
       stat.inc_deduped_young(size_in_bytes);
     } else {
       stat.inc_deduped_old(size_in_bytes);
     }
   }
 }
 G1StringDedupTable* G1StringDedupTable::prepare_resize() {
   size_t size = _table->_size;
   // Check if the hashtable needs to be resized
   if (_table->_entries > _table->_grow_threshold) {
     // Grow table, double the size
     size *= 2;
     if (size > _max_size) {
       // Too big, don't resize
       return NULL;
     }
   } else if (_table->_entries < _table->_shrink_threshold) {
     // Shrink table, half the size
     size /= 2;
     if (size < _min_size) {
       // Too small, don't resize
       return NULL;
     }
   } else if (StringDeduplicationResizeALot) {
     // Force grow
     size *= 2;
     if (size > _max_size) {
       // Too big, force shrink instead
       size /= 4;
     }
   } else {
     // Resize not needed
     return NULL;
   }
   // Update statistics
   _resize_count++;
   // Update max cache size
   _entry_cache->set_max_size((size_t)(size * _max_cache_factor));
   // Allocate the new table. The new table will be populated by workers
   // calling unlink_or_oops_do() and finally installed by finish_resize().
   return new G1StringDedupTable(size, _table->_hash_seed);
 }
 void G1StringDedupTable::finish_resize(G1StringDedupTable* resized_table) {
   assert(resized_table != NULL, "Invalid table");
   resized_table->_entries = _table->_entries;
   // Free old table
   delete _table;
   // Install new table
   _table = resized_table;
 }
 void G1StringDedupTable::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, uint worker_id) {
   // The table is divided into partitions to allow lock-less parallel processing by
   // multiple worker threads. A worker thread first claims a partition, which ensures
   // exclusive access to that part of the table, then continues to process it. To allow
   // shrinking of the table in parallel we also need to make sure that the same worker
   // thread processes all partitions where entries will hash to the same destination
   // partition. Since the table size is always a power of two and we always shrink by
   // dividing the table in half, we know that for a given partition there is only one
   // other partition whoes entries will hash to the same destination partition. That
   // other partition is always the sibling partition in the second half of the table.
   // For example, if the table is divided into 8 partitions, the sibling of partition 0
   // is partition 4, the sibling of partition 1 is partition 5, etc.
   size_t table_half = _table->_size / 2;
   // Let each partition be one page worth of buckets
   size_t partition_size = MIN2(table_half, os::vm_page_size() / sizeof(G1StringDedupEntry*));
   assert(table_half % partition_size == 0, "Invalid partition size");
   // Number of entries removed during the scan
   uintx removed = 0;
   for (;;) {
     // Grab next partition to scan
     size_t partition_begin = cl->claim_table_partition(partition_size);
     size_t partition_end = partition_begin + partition_size;
     if (partition_begin >= table_half) {
       // End of table
       break;
     }
     // Scan the partition followed by the sibling partition in the second half of the table
     removed += unlink_or_oops_do(cl, partition_begin, partition_end, worker_id);
     removed += unlink_or_oops_do(cl, table_half + partition_begin, table_half + partition_end, worker_id);
   }
   // Delayed update to avoid contention on the table lock
   if (removed > 0) {
     MutexLockerEx ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag);
     _table->_entries -= removed;
     _entries_removed += removed;
   }
 }
 uintx G1StringDedupTable::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl,
                                             size_t partition_begin,
                                             size_t partition_end,
                                             uint worker_id) {
   uintx removed = 0;
   for (size_t bucket = partition_begin; bucket < partition_end; bucket++) {
     G1StringDedupEntry** entry = _table->bucket(bucket);
     while (*entry != NULL) {
       oop* p = (oop*)(*entry)->obj_addr();
       if (cl->is_alive(*p)) {
         cl->keep_alive(p);
         if (cl->is_resizing()) {
           // We are resizing the table, transfer entry to the new table
           _table->transfer(entry, cl->resized_table());
         } else {
           if (cl->is_rehashing()) {
             // We are rehashing the table, rehash the entry but keep it
             // in the table. We can't transfer entries into the new table
             // at this point since we don't have exclusive access to all
             // destination partitions. finish_rehash() will do a single
             // threaded transfer of all entries.
             typeArrayOop value = (typeArrayOop)*p;
             assert(!use_java_hash(), "Should not be using Java hash");
             uint64_t hash = alt_hash_code(value);
             (*entry)->set_alt_hash(hash);
           }
           // Move to next entry
           entry = (*entry)->next_addr();
         }
       } else {
         // Not alive, remove entry from table
         _table->remove(entry, worker_id);
         removed++;
       }
     }
   }
   return removed;
 }
 G1StringDedupTable* G1StringDedupTable::prepare_rehash() {
   if (!_table->_rehash_needed && !StringDeduplicationRehashALot) {
     // Rehash not needed
     return NULL;
   }
   // Update statistics
   _rehash_count++;
   // Compute new hash seed
   _table->_hash_seed = AltHashing::compute_seed();
   // Allocate the new table, same size and hash seed
   return new G1StringDedupTable(_table->_size, _table->_hash_seed);
 }
 void G1StringDedupTable::finish_rehash(G1StringDedupTable* rehashed_table) {
   assert(rehashed_table != NULL, "Invalid table");
   // Move all newly rehashed entries into the correct buckets in the new table
   for (size_t bucket = 0; bucket < _table->_size; bucket++) {
     G1StringDedupEntry** entry = _table->bucket(bucket);
     while (*entry != NULL) {
       _table->transfer(entry, rehashed_table);
     }
   }
   rehashed_table->_entries = _table->_entries;
   // Free old table
   delete _table;
   // Install new table
   _table = rehashed_table;
 }
 void G1StringDedupTable::verify() {
   for (size_t bucket = 0; bucket < _table->_size; bucket++) {
     // Verify entries
     G1StringDedupEntry** entry = _table->bucket(bucket);
     while (*entry != NULL) {
       typeArrayOop value = (*entry)->obj();
       guarantee(value != NULL, "Object must not be NULL");
       guarantee(Universe::heap()->is_in_reserved(value), "Object must be on the heap");
       guarantee(!value->is_forwarded(), "Object must not be forwarded");
       guarantee(value->is_typeArray(), "Object must be a typeArrayOop");
       uint64_t hash;
       if (use_java_hash()) {
         hash = (*entry)->java_hash();
         guarantee(java_hash_code(value) == hash, "Table entry has incorrect hash");
       } else {
         hash = (*entry)->alt_hash();
         guarantee(alt_hash_code(value) == hash, "Table entry has incorrect hash");
       }
       guarantee(_table->hash_to_index(hash) == bucket, "Table entry has incorrect index");
       entry = (*entry)->next_addr();
     }
     // Verify that we do not have entries with identical oops or identical arrays.
     // We only need to compare entries in the same bucket. If the same oop or an
     // identical array has been inserted more than once into different/incorrect
     // buckets the verification step above will catch that.
     G1StringDedupEntry** entry1 = _table->bucket(bucket);
     while (*entry1 != NULL) {
       typeArrayOop value1 = (*entry1)->obj();
       G1StringDedupEntry** entry2 = (*entry1)->next_addr();
       while (*entry2 != NULL) {
         typeArrayOop value2 = (*entry2)->obj();
         guarantee(value1 != value2, "Table entries must not have the same array");
         if (use_java_hash()) {
           guarantee(!equals(value1, value2), "Table entries must not have identical arrays");
         }
         entry2 = (*entry2)->next_addr();
       }
       entry1 = (*entry1)->next_addr();
     }
   }
 }
 void G1StringDedupTable::clean_entry_cache() {
   _entry_cache->delete_overflowed();
 }
 void G1StringDedupTable::print_statistics(outputStream* st) {
   st->print_cr(
     "   [Table]\n"
     "      [Memory Usage: " G1_STRDEDUP_BYTES_FORMAT_NS "]\n"
     "      [Size: " SIZE_FORMAT ", Min: " SIZE_FORMAT ", Max: " SIZE_FORMAT "]\n"
     "      [Entries: " UINTX_FORMAT ", Load: " G1_STRDEDUP_PERCENT_FORMAT_NS ", Cached: " UINTX_FORMAT ", Added: " UINTX_FORMAT ", Removed: " UINTX_FORMAT "]\n"
     "      [Resize Count: " UINTX_FORMAT ", Shrink Threshold: " UINTX_FORMAT "(" G1_STRDEDUP_PERCENT_FORMAT_NS "), Grow Threshold: " UINTX_FORMAT "(" G1_STRDEDUP_PERCENT_FORMAT_NS ")]\n"
     "      [Rehash Count: " UINTX_FORMAT ", Rehash Threshold: " UINTX_FORMAT ", Hash Seed: " UINT64_FORMAT_X "]\n"
     "      [Age Threshold: " UINTX_FORMAT "]",
     G1_STRDEDUP_BYTES_PARAM(_table->_size * sizeof(G1StringDedupEntry*) + (_table->_entries + _entry_cache->size()) * sizeof(G1StringDedupEntry)),
     _table->_size, _min_size, _max_size,
     _table->_entries, (double)_table->_entries / (double)_table->_size * 100.0, _entry_cache->size(), _entries_added, _entries_removed,
     _resize_count, _table->_shrink_threshold, _shrink_load_factor * 100.0, _table->_grow_threshold, _grow_load_factor * 100.0,
     _rehash_count, _rehash_threshold, _table->_hash_seed,
     StringDeduplicationAgeThreshold);
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/g1/g1StringDedupTable.cpp@fd3484fadbe3 (annotated)

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