view src/share/vm/gc_implementation/g1/g1MMUTracker.hpp @ 2981:2ace1c4ee8da

6888336: G1: avoid explicitly marking and pushing objects in survivor spaces Summary: This change simplifies the interaction between GC and concurrent marking. By disabling survivor spaces during the initial-mark pause we don't need to propagate marks of objects we copy during each GC (since we never need to copy an explicitly marked object). Reviewed-by: johnc, brutisso
author tonyp
date Tue, 10 Jan 2012 18:58:13 -0500
parents c18cbe5936b8
children d2a62e0f25eb
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 * published by the Free Software Foundation.
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 * 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.
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#include "memory/allocation.hpp"
#include "utilities/debug.hpp"

// Keeps track of the GC work and decides when it is OK to do GC work
// and for how long so that the MMU invariants are maintained.

/***** ALL TIMES ARE IN SECS!!!!!!! *****/

// this is the "interface"
class G1MMUTracker: public CHeapObj {
  double          _time_slice;
  double          _max_gc_time; // this is per time slice

  G1MMUTracker(double time_slice, double max_gc_time);

  virtual void add_pause(double start, double end, bool gc_thread) = 0;
  virtual double longest_pause(double current_time) = 0;
  virtual double when_sec(double current_time, double pause_time) = 0;

  double max_gc_time() {
    return _max_gc_time;

  inline bool now_max_gc(double current_time) {
    return when_sec(current_time, max_gc_time()) < 0.00001;

  inline double when_max_gc_sec(double current_time) {
    return when_sec(current_time, max_gc_time());

  inline jlong when_max_gc_ms(double current_time) {
    double when = when_max_gc_sec(current_time);
    return (jlong) (when * 1000.0);

  inline jlong when_ms(double current_time, double pause_time) {
    double when = when_sec(current_time, pause_time);
    return (jlong) (when * 1000.0);

class G1MMUTrackerQueueElem VALUE_OBJ_CLASS_SPEC {
  double _start_time;
  double _end_time;

  inline double start_time() { return _start_time; }
  inline double end_time()   { return _end_time; }
  inline double duration()   { return _end_time - _start_time; }

  G1MMUTrackerQueueElem() {
    _start_time = 0.0;
    _end_time   = 0.0;

  G1MMUTrackerQueueElem(double start_time, double end_time) {
    _start_time = start_time;
    _end_time   = end_time;

// this is an implementation of the MMUTracker using a (fixed-size) queue
// that keeps track of all the recent pause times
class G1MMUTrackerQueue: public G1MMUTracker {
  enum PrivateConstants {
    QueueLength = 64

  // The array keeps track of all the pauses that fall within a time
  // slice (the last time slice during which pauses took place).
  // The data structure implemented is a circular queue.
  // Head "points" to the most recent addition, tail to the oldest one.
  // The array is of fixed size and I don't think we'll need more than
  // two or three entries with the current behaviour of G1 pauses.
  // If the array is full, an easy fix is to look for the pauses with
  // the shortest gap between them and consolidate them.
  // For now, we have taken the expedient alternative of forgetting
  // the oldest entry in the event that +G1UseFixedWindowMMUTracker, thus
  // potentially violating MMU specs for some time thereafter.

  G1MMUTrackerQueueElem _array[QueueLength];
  int                   _head_index;
  int                   _tail_index;
  int                   _no_entries;

  inline int trim_index(int index) {
    return (index + QueueLength) % QueueLength;

  void remove_expired_entries(double current_time);
  double calculate_gc_time(double current_time);

  double longest_pause_internal(double current_time);
  double when_internal(double current_time, double pause_time);

  G1MMUTrackerQueue(double time_slice, double max_gc_time);

  virtual void add_pause(double start, double end, bool gc_thread);

  virtual double longest_pause(double current_time);
  virtual double when_sec(double current_time, double pause_time);