view src/share/vm/gc_implementation/g1/concurrentG1Refine.hpp @ 1625:2d160770d2e5

6814437: G1: remove the _new_refs array Summary: The per-worker _new_refs array is used to hold references that point into the collection set. It is populated during RSet updating and subsequently processed. In the event of an evacuation failure it processed again to recreate the RSets of regions in the collection set. Remove the per-worker _new_refs array by processing the references directly. Use a DirtyCardQueue to hold the cards containing the references so that the RSets of regions in the collection set can be recreated when handling an evacuation failure. Reviewed-by: iveresov, jmasa, tonyp
author johnc
date Mon, 02 Aug 2010 12:51:43 -0700
parents c18cbe5936b8
children f95d63e2154a
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 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 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;
  int _n_worker_threads;
  * The value of the update buffer queue length falls into one of 3 zones:
  * green, yellow, red. If the value is in [0, green) nothing is
  * done, the buffers are left unprocessed to enable the caching effect of the
  * dirtied cards. In the yellow zone [green, yellow) the concurrent refinement
  * threads are gradually activated. In [yellow, red) all threads are
  * running. If the length becomes red (max queue length) the mutators start
  * processing the buffers.
  * There are some interesting cases (when G1UseAdaptiveConcRefinement
  * is turned off):
  * 1) green = yellow = red = 0. In this case the mutator will process all
  *    buffers. Except for those that are created by the deferred updates
  *    machinery during a collection.
  * 2) green = 0. Means no caching. Can be a good way to minimize the
  *    amount of time spent updating rsets during a collection.
  int _green_zone;
  int _yellow_zone;
  int _red_zone;

  int _thread_threshold_step;

  // Reset the threshold step value based of the current zone boundaries.
  void reset_threshold_step();

  // 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();

  void reinitialize_threads();

  // 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, DirtyCardQueue* into_cset_dcq);

  // 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 int thread_num();

  void print_worker_threads_on(outputStream* st) const;

  void set_green_zone(int x)  { _green_zone = x;  }
  void set_yellow_zone(int x) { _yellow_zone = x; }
  void set_red_zone(int x)    { _red_zone = x;    }

  int green_zone() const      { return _green_zone;  }
  int yellow_zone() const     { return _yellow_zone; }
  int red_zone() const        { return _red_zone;    }

  int total_thread_num() const  { return _n_threads;        }
  int worker_thread_num() const { return _n_worker_threads; }

  int thread_threshold_step() const { return _thread_threshold_step; }