g1MMUTracker.hpp revision 8413:92457dfb91bd 
1/*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#ifndef SHARE_VM_GC_G1_G1MMUTRACKER_HPP
26#define SHARE_VM_GC_G1_G1MMUTRACKER_HPP
27
28#include "memory/allocation.hpp"
29#include "utilities/debug.hpp"
30
31// Keeps track of the GC work and decides when it is OK to do GC work
32// and for how long so that the MMU invariants are maintained.
33
34/***** ALL TIMES ARE IN SECS!!!!!!! *****/
35
36// this is the "interface"
37class G1MMUTracker: public CHeapObj<mtGC> {
38protected:
39  double          _time_slice;
40  double          _max_gc_time; // this is per time slice
41
42public:
43  G1MMUTracker(double time_slice, double max_gc_time);
44
45  virtual void add_pause(double start, double end, bool gc_thread) = 0;
46  virtual double when_sec(double current_time, double pause_time) = 0;
47
48  double max_gc_time() {
49    return _max_gc_time;
50  }
51
52  inline bool now_max_gc(double current_time) {
53    return when_sec(current_time, max_gc_time()) < 0.00001;
54  }
55
56  inline double when_max_gc_sec(double current_time) {
57    return when_sec(current_time, max_gc_time());
58  }
59
60  inline jlong when_max_gc_ms(double current_time) {
61    double when = when_max_gc_sec(current_time);
62    return (jlong) (when * 1000.0);
63  }
64
65  inline jlong when_ms(double current_time, double pause_time) {
66    double when = when_sec(current_time, pause_time);
67    return (jlong) (when * 1000.0);
68  }
69};
70
71class G1MMUTrackerQueueElem VALUE_OBJ_CLASS_SPEC {
72private:
73  double _start_time;
74  double _end_time;
75
76public:
77  inline double start_time() { return _start_time; }
78  inline double end_time()   { return _end_time; }
79  inline double duration()   { return _end_time - _start_time; }
80
81  G1MMUTrackerQueueElem() {
82    _start_time = 0.0;
83    _end_time   = 0.0;
84  }
85
86  G1MMUTrackerQueueElem(double start_time, double end_time) {
87    _start_time = start_time;
88    _end_time   = end_time;
89  }
90};
91
92// this is an implementation of the MMUTracker using a (fixed-size) queue
93// that keeps track of all the recent pause times
94class G1MMUTrackerQueue: public G1MMUTracker {
95private:
96  enum PrivateConstants {
97    QueueLength = 64
98  };
99
100  // The array keeps track of all the pauses that fall within a time
101  // slice (the last time slice during which pauses took place).
102  // The data structure implemented is a circular queue.
103  // Head "points" to the most recent addition, tail to the oldest one.
104  // The array is of fixed size and I don't think we'll need more than
105  // two or three entries with the current behavior of G1 pauses.
106  // If the array is full, an easy fix is to look for the pauses with
107  // the shortest gap between them and consolidate them.
108  // For now, we have taken the expedient alternative of forgetting
109  // the oldest entry in the event that +G1UseFixedWindowMMUTracker, thus
110  // potentially violating MMU specs for some time thereafter.
111
112  G1MMUTrackerQueueElem _array[QueueLength];
113  int                   _head_index;
114  int                   _tail_index;
115  int                   _no_entries;
116
117  inline int trim_index(int index) {
118    return (index + QueueLength) % QueueLength;
119  }
120
121  void remove_expired_entries(double current_time);
122  double calculate_gc_time(double current_time);
123
124  double when_internal(double current_time, double pause_time);
125
126public:
127  G1MMUTrackerQueue(double time_slice, double max_gc_time);
128
129  virtual void add_pause(double start, double end, bool gc_thread);
130
131  virtual double when_sec(double current_time, double pause_time);
132};
133
134#endif // SHARE_VM_GC_G1_G1MMUTRACKER_HPP
135