/*

 * 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.

 *

 */

#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 "memory/gcLocker.hpp"

#include "memory/padded.inline.hpp"

#include "oops/typeArrayOop.hpp"

#include "runtime/mutexLocker.hpp"

//

// Freelist in the deduplication table entry cache. Links table

// entries together using their _next fields.

//

class G1StringDedupEntryFreeList : public CHeapObj<mtGC> {

private:

  G1StringDedupEntry* _list;

  size_t              _length;

public:

  G1StringDedupEntryFreeList() :

    _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;

  }

  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 freelist per GC worker to allow lock less freeing of

  // entries while doing a parallel scan of the table. Using

  // PaddedEnd to avoid false sharing.

  PaddedEnd<G1StringDedupEntryFreeList>* _lists;

  size_t                                 _nlists;

public:

  G1StringDedupEntryCache();

  ~G1StringDedupEntryCache();

  // Get a table entry from the cache freelist, or allocate a new

  // entry if the cache is empty.

  G1StringDedupEntry* alloc();

  // Insert a table entry into the cache freelist.

  void free(G1StringDedupEntry* entry, uint worker_id);

  // Returns current number of entries in the cache.

  size_t size();

  // If the cache has grown above the given max size, trim it down

  // and deallocate the memory occupied by trimmed of entries.

  void trim(size_t max_size);

};

G1StringDedupEntryCache::G1StringDedupEntryCache() {

  _nlists = MAX2(ParallelGCThreads, (size_t)1);

  _lists = PaddedArray<G1StringDedupEntryFreeList, mtGC>::create_unfreeable((uint)_nlists);

}

G1StringDedupEntryCache::~G1StringDedupEntryCache() {

  ShouldNotReachHere();

}

G1StringDedupEntry* G1StringDedupEntryCache::alloc() {

  for (size_t i = 0; i < _nlists; i++) {

    G1StringDedupEntry* entry = _lists[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);

  _lists[worker_id].add(entry);

}

size_t G1StringDedupEntryCache::size() {

  size_t size = 0;

  for (size_t i = 0; i < _nlists; i++) {

    size += _lists[i].length();

  }

  return size;

}

void G1StringDedupEntryCache::trim(size_t max_size) {

  size_t cache_size = 0;

  for (size_t i = 0; i < _nlists; i++) {

    G1StringDedupEntryFreeList* list = &_lists[i];

    cache_size += list->length();

    while (cache_size > max_size) {

      G1StringDedupEntry* entry = list->remove();

      assert(entry != NULL, "Should not be null");

      cache_size--;

      delete entry;

    }

  }

}

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, jint 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();

  _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::murmur3_32(_table->_hash_seed, 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++;

  // 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 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();

    }