Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * 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.

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  */

 #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_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, unsigned int hash, G1StringDedupEntry** list) {

   G1StringDedupEntry* entry = _entry_cache->alloc();

   entry->set_obj(value);

   entry->set_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();

   unsigned int hash = entry->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, unsigned int hash,

                                         G1StringDedupEntry** list, uintx &count) {

   for (G1StringDedupEntry* entry = *list; entry != NULL; entry = entry->next()) {

     if (entry->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, unsigned int 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::hash_code(typeArrayOop value) {

   unsigned int hash;

   int length = value->length();

   const jchar* data = (jchar*)value->base(T_CHAR);

   if (use_java_hash()) {

     hash = java_lang_String::hash_code(data, length);

   } else {

     hash = AltHashing::halfsiphash_32(_table->_hash_seed, (const uint16_t*)data, length);

   }

   return hash;

 }

 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;

   }

   unsigned int hash = 0;

   if (use_java_hash()) {

     // Get hash code from cache

     hash = java_lang_String::hash(java_string);

   }

   if (hash == 0) {

     // Compute hash

     hash = 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;

             unsigned int hash = hash_code(value);

             (*entry)->set_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");

       unsigned int hash = hash_code(value);

       guarantee((*entry)->hash() == hash, "Table entry has inorrect 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(!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 "]\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);

 }