/*

 * Copyright (c) 2014, 2019, 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.inline.hpp"

#include "gc/shared/stringdedup/stringDedup.hpp"

#include "gc/shared/stringdedup/stringDedupTable.hpp"

#include "gc/shared/suspendibleThreadSet.hpp"

#include "logging/log.hpp"

#include "memory/padded.inline.hpp"

#include "memory/universe.hpp"

#include "oops/access.inline.hpp"

#include "oops/arrayOop.inline.hpp"

#include "oops/oop.inline.hpp"

#include "oops/typeArrayOop.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/safepointVerifiers.hpp"

//

// List of deduplication table entries. Links table

// entries together using their _next fields.

//

class StringDedupEntryList : public CHeapObj<mtGC> {

private:

  StringDedupEntry*   _list;

  size_t              _length;

public:

  StringDedupEntryList() :

    _list(NULL),

    _length(0) {

  }

  void add(StringDedupEntry* entry) {

    entry->set_next(_list);

    _list = entry;

    _length++;

  }

  StringDedupEntry* remove() {

    StringDedupEntry* entry = _list;

    if (entry != NULL) {

      _list = entry->next();

      _length--;

    }

    return entry;

  }

  StringDedupEntry* remove_all() {

    StringDedupEntry* 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 StringDedupEntryCache : 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<StringDedupEntryList>*   _cached;

  PaddedEnd<StringDedupEntryList>*   _overflowed;

public:

  StringDedupEntryCache(size_t max_size);

  ~StringDedupEntryCache();

  // 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.

  StringDedupEntry* alloc();

  // Insert a table entry into the cache.

  void free(StringDedupEntry* entry, uint worker_id);

  // Returns current number of entries in the cache.

  size_t size();

  // Deletes overflowed entries.

  void delete_overflowed();

};

StringDedupEntryCache::StringDedupEntryCache(size_t max_size) :

  _nlists(ParallelGCThreads),

  _max_list_length(0),

  _cached(PaddedArray<StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)),

  _overflowed(PaddedArray<StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)) {

  set_max_size(max_size);

}

StringDedupEntryCache::~StringDedupEntryCache() {

  ShouldNotReachHere();

}

void StringDedupEntryCache::set_max_size(size_t size) {

  _max_list_length = size / _nlists;

}

StringDedupEntry* StringDedupEntryCache::alloc() {

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

    StringDedupEntry* entry = _cached[i].remove();

    if (entry != NULL) {

      return entry;

    }

  }

  return new StringDedupEntry();

}

void StringDedupEntryCache::free(StringDedupEntry* 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 StringDedupEntryCache::size() {

  size_t size = 0;

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

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

  }

  return size;

}

void StringDedupEntryCache::delete_overflowed() {

  double start = os::elapsedTime();

  uintx count = 0;

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

    StringDedupEntry* 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) {

      StringDedupEntry* next = entry->next();

      delete entry;

      entry = next;

      count++;

    }

  }

  double end = os::elapsedTime();

  log_trace(gc, stringdedup)("Deleted " UINTX_FORMAT " entries, " STRDEDUP_TIME_FORMAT_MS,

                             count, STRDEDUP_TIME_PARAM_MS(end - start));

}

StringDedupTable*        StringDedupTable::_table = NULL;

StringDedupEntryCache*   StringDedupTable::_entry_cache = NULL;

const size_t             StringDedupTable::_min_size = (1 << 10);   // 1024

const size_t             StringDedupTable::_max_size = (1 << 24);   // 16777216

const double             StringDedupTable::_grow_load_factor = 2.0; // Grow table at 200% load

const double             StringDedupTable::_shrink_load_factor = _grow_load_factor / 3.0; // Shrink table at 67% load

const double             StringDedupTable::_max_cache_factor = 0.1; // Cache a maximum of 10% of the table size

const uintx              StringDedupTable::_rehash_multiple = 60;   // Hash bucket has 60 times more collisions than expected

const uintx              StringDedupTable::_rehash_threshold = (uintx)(_rehash_multiple * _grow_load_factor);

uintx                    StringDedupTable::_entries_added = 0;

uintx                    StringDedupTable::_entries_removed = 0;

uintx                    StringDedupTable::_resize_count = 0;

uintx                    StringDedupTable::_rehash_count = 0;

StringDedupTable*        StringDedupTable::_resized_table = NULL;

StringDedupTable*        StringDedupTable::_rehashed_table = NULL;

volatile size_t          StringDedupTable::_claimed_index = 0;

StringDedupTable::StringDedupTable(size_t size, jint hash_seed) :

  _size(size),

  _entries(0),

  _shrink_threshold((uintx)(size * _shrink_load_factor)),

  _grow_threshold((uintx)(size * _grow_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(StringDedupEntry*, _size, mtGC);

  memset(_buckets, 0, _size * sizeof(StringDedupEntry*));

}

StringDedupTable::~StringDedupTable() {

  FREE_C_HEAP_ARRAY(G1StringDedupEntry*, _buckets);

}

void StringDedupTable::create() {

  assert(_table == NULL, "One string deduplication table allowed");

  _entry_cache = new StringDedupEntryCache(_min_size * _max_cache_factor);

  _table = new StringDedupTable(_min_size);

}

void StringDedupTable::add(typeArrayOop value, bool latin1, unsigned int hash, StringDedupEntry** list) {

  StringDedupEntry* entry = _entry_cache->alloc();

  entry->set_obj(value);

  entry->set_hash(hash);

  entry->set_latin1(latin1);

  entry->set_next(*list);

  *list = entry;

  _entries++;

}

void StringDedupTable::remove(StringDedupEntry** pentry, uint worker_id) {

  StringDedupEntry* entry = *pentry;

  *pentry = entry->next();

  _entry_cache->free(entry, worker_id);

}

void StringDedupTable::transfer(StringDedupEntry** pentry, StringDedupTable* dest) {

  StringDedupEntry* entry = *pentry;

  *pentry = entry->next();

  unsigned int hash = entry->hash();

  size_t index = dest->hash_to_index(hash);

  StringDedupEntry** list = dest->bucket(index);

  entry->set_next(*list);

  *list = entry;

}

typeArrayOop StringDedupTable::lookup(typeArrayOop value, bool latin1, unsigned int hash,

                                      StringDedupEntry** list, uintx &count) {

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

    if (entry->hash() == hash && entry->latin1() == latin1) {

      oop* obj_addr = (oop*)entry->obj_addr();

      oop obj = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(obj_addr);

      if (java_lang_String::value_equals(value, static_cast<typeArrayOop>(obj))) {

        obj = NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(obj_addr);

        return static_cast<typeArrayOop>(obj);

      }

    }

    count++;

  }

  // Not found

  return NULL;

}

typeArrayOop StringDedupTable::lookup_or_add_inner(typeArrayOop value, bool latin1, unsigned int hash) {

  size_t index = hash_to_index(hash);

  StringDedupEntry** list = bucket(index);

  uintx count = 0;

  // Lookup in list

  typeArrayOop existing_value = lookup(value, latin1, 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, latin1, hash, list);

    // Update statistics

    _entries_added++;

  }

  return existing_value;

}

unsigned int StringDedupTable::hash_code(typeArrayOop value, bool latin1) {

  unsigned int hash;

  int length = value->length();

  if (latin1) {

    const jbyte* data = (jbyte*)value->base(T_BYTE);

    if (use_java_hash()) {

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

    } else {

      hash = AltHashing::murmur3_32(_table->_hash_seed, data, length);

    }

  } else {

    length /= sizeof(jchar) / sizeof(jbyte); // Convert number of bytes to number of chars

    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 StringDedupTable::deduplicate(oop java_string, StringDedupStat* stat) {

  assert(java_lang_String::is_instance(java_string), "Must be a string");

  NoSafepointVerifier nsv;

  stat->inc_inspected();

  typeArrayOop value = java_lang_String::value(java_string);

  if (value == NULL) {

    // String has no value

    stat->inc_skipped();

    return;

  }

  bool latin1 = java_lang_String::is_latin1(java_string);

  unsigned int hash = 0;

  if (use_java_hash()) {

    if (!java_lang_String::hash_is_set(java_string)) {

      stat->inc_hashed();

    }

    hash = java_lang_String::hash_code(java_string);

  } else {

    // Compute hash

    hash = hash_code(value, latin1);

    stat->inc_hashed();

  }

  typeArrayOop existing_value = lookup_or_add(value, latin1, 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) {

    // Existing value found, deduplicate string

    java_lang_String::set_value(java_string, existing_value);

    stat->deduped(value, size_in_bytes);

  }

}

bool StringDedupTable::is_resizing() {

  return _resized_table != NULL;

}

bool StringDedupTable::is_rehashing() {

  return _rehashed_table != NULL;

}

StringDedupTable* StringDedupTable::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 * _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 StringDedupTable(size, _table->_hash_seed);

}

void StringDedupTable::finish_resize(StringDedupTable* 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 StringDedupTable::unlink_or_oops_do(StringDedupUnlinkOrOopsDoClosure* 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(StringDedupEntry*));

  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 = 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) {

    MutexLocker ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag);

    _table->_entries -= removed;

    _entries_removed += removed;

  }

}

uintx StringDedupTable::unlink_or_oops_do(StringDedupUnlinkOrOopsDoClosure* 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++) {

    StringDedupEntry** entry = _table->bucket(bucket);

    while (*entry != NULL) {

      oop* p = (oop*)(*entry)->obj_addr();

      if (cl->is_alive(*p)) {

        cl->keep_alive(p);

        if (is_resizing()) {

          // We are resizing the table, transfer entry to the new table

          _table->transfer(entry, _resized_table);

        } else {

          if (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;

            bool latin1 = (*entry)->latin1();

            unsigned int hash = hash_code(value, latin1);

            (*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;

}