view src/share/vm/gc_implementation/g1/concurrentG1Refine.hpp @ 890:6cb8e9df7174

6819077: G1: first GC thread coming late into the GC. Summary: The first worker thread is delayed when entering the GC because it clears the card count table that is used in identifying hot cards. Replace the card count table with a dynamically sized evicting hash table that includes an epoch based counter. Reviewed-by: iveresov, tonyp
author johnc
date Tue, 04 Aug 2009 16:00:17 -0700
parents 15c5903cf9e1
children 035d2e036a9b
line wrap: on
line source
 * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit if you need additional information or
 * have any questions.

// Forward decl
class ConcurrentG1RefineThread;
class G1RemSet;

class ConcurrentG1Refine: public CHeapObj {
  ConcurrentG1RefineThread** _threads;
  int _n_threads;

  // The cache for card refinement.
  bool   _use_cache;
  bool   _def_use_cache;

  size_t _n_periods;    // Used as clearing epoch

  // An evicting cache of the number of times each card
  // is accessed. Reduces, but does not eliminate, the amount
  // of duplicated processing of dirty cards.

  enum SomePrivateConstants {
    epoch_bits           = 32,
    card_num_shift       = epoch_bits,
    epoch_mask           = AllBits,
    card_num_mask        = AllBits,

    // The initial cache size is approximately this fraction
    // of a maximal cache (i.e. the size needed for all cards
    // in the heap)
    InitialCacheFraction = 512

  const static julong card_num_mask_in_place =
                        (julong) card_num_mask << card_num_shift;

  typedef struct {
    julong _value;      // |  card_num   |  epoch   |
  } CardEpochCacheEntry;

  julong make_epoch_entry(unsigned int card_num, unsigned int epoch) {
    assert(0 <= card_num && card_num < _max_n_card_counts, "Bounds");
    assert(0 <= epoch && epoch <= _n_periods, "must be");

    return ((julong) card_num << card_num_shift) | epoch;

  unsigned int extract_epoch(julong v) {
    return (v & epoch_mask);

  unsigned int extract_card_num(julong v) {
    return (v & card_num_mask_in_place) >> card_num_shift;

  typedef struct {
    unsigned char _count;
    unsigned char _evict_count;
  } CardCountCacheEntry;

  CardCountCacheEntry* _card_counts;
  CardEpochCacheEntry* _card_epochs;

  // The current number of buckets in the card count cache
  unsigned _n_card_counts;

  // The max number of buckets required for the number of
  // cards for the entire reserved heap
  unsigned _max_n_card_counts;

  // Possible sizes of the cache: odd primes that roughly double in size.
  // (See jvmtiTagMap.cpp).
  static int _cc_cache_sizes[];

  // The index in _cc_cache_sizes corresponding to the size of
  // _card_counts.
  int _cache_size_index;

  bool _expand_card_counts;

  const jbyte* _ct_bot;

  jbyte**      _hot_cache;
  int          _hot_cache_size;
  int          _n_hot;
  int          _hot_cache_idx;

  int          _hot_cache_par_chunk_size;
  volatile int _hot_cache_par_claimed_idx;

  // Needed to workaround 6817995
  CardTableModRefBS* _ct_bs;
  G1CollectedHeap*   _g1h;

  // Expands the array that holds the card counts to the next size up
  void expand_card_count_cache();

  // hash a given key (index of card_ptr) with the specified size
  static unsigned int hash(size_t key, int size) {
    return (unsigned int) key % size;

  // hash a given key (index of card_ptr)
  unsigned int hash(size_t key) {
    return hash(key, _n_card_counts);

  unsigned ptr_2_card_num(jbyte* card_ptr) {
    return (unsigned) (card_ptr - _ct_bot);

  jbyte* card_num_2_ptr(unsigned card_num) {
    return (jbyte*) (_ct_bot + card_num);

  // Returns the count of this card after incrementing it.
  jbyte* add_card_count(jbyte* card_ptr, int* count, bool* defer);

  // Returns true if this card is in a young region
  bool is_young_card(jbyte* card_ptr);


  void init(); // Accomplish some initialization that has to wait.
  void stop();

  // Iterate over the conc refine threads
  void threads_do(ThreadClosure *tc);

  // If this is the first entry for the slot, writes into the cache and
  // returns NULL.  If it causes an eviction, returns the evicted pointer.
  // Otherwise, its a cache hit, and returns NULL.
  jbyte* cache_insert(jbyte* card_ptr, bool* defer);

  // Process the cached entries.
  void clean_up_cache(int worker_i, G1RemSet* g1rs);

  // Set up for parallel processing of the cards in the hot cache
  void clear_hot_cache_claimed_index() {
    _hot_cache_par_claimed_idx = 0;

  // Discard entries in the hot cache.
  void clear_hot_cache() {
    _hot_cache_idx = 0; _n_hot = 0;

  bool hot_cache_is_empty() { return _n_hot == 0; }

  bool use_cache() { return _use_cache; }
  void set_use_cache(bool b) {
    if (b) _use_cache = _def_use_cache;
    else   _use_cache = false;

  void clear_and_record_card_counts();

  static size_t thread_num();