1/*
2 * Copyright (c) 2001, 2016, 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.
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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
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23 */
24
25#ifndef SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
26#define SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
27
28#include "gc/cms/concurrentMarkSweepGeneration.hpp"
29#include "gc/shared/concurrentGCThread.hpp"
30#include "runtime/thread.hpp"
31
32class ConcurrentMarkSweepGeneration;
33class CMSCollector;
34
35// The Concurrent Mark Sweep GC Thread
36class ConcurrentMarkSweepThread: public ConcurrentGCThread {
37  friend class VMStructs;
38  friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
39  friend class CMSCollector;
40
41 private:
42  static ConcurrentMarkSweepThread* _cmst;
43  static CMSCollector*              _collector;
44
45  enum CMS_flag_type {
46    CMS_nil             = NoBits,
47    CMS_cms_wants_token = nth_bit(0),
48    CMS_cms_has_token   = nth_bit(1),
49    CMS_vm_wants_token  = nth_bit(2),
50    CMS_vm_has_token    = nth_bit(3)
51  };
52
53  static int _CMS_flag;
54
55  static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
56  static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
57  static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
58  void sleepBeforeNextCycle();
59
60  // CMS thread should yield for a young gen collection and direct allocations
61  static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
62  static volatile jint _pending_yields;
63  static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
64
65  // debugging
66  void verify_ok_to_terminate() const PRODUCT_RETURN;
67
68  void run_service();
69  void stop_service();
70
71 public:
72  // Constructor
73  ConcurrentMarkSweepThread(CMSCollector* collector);
74
75  static void threads_do(ThreadClosure* tc);
76
77  // Printing
78  static void print_all_on(outputStream* st);
79  static void print_all()                             { print_all_on(tty); }
80
81  // Returns the CMS Thread
82  static ConcurrentMarkSweepThread* cmst()    { return _cmst; }
83  static CMSCollector*         collector()    { return _collector;  }
84
85  // Create and start the CMS Thread, or stop it on shutdown
86  static ConcurrentMarkSweepThread* start(CMSCollector* collector);
87
88  // Synchronization using CMS token
89  static void synchronize(bool is_cms_thread);
90  static void desynchronize(bool is_cms_thread);
91  static bool vm_thread_has_cms_token() {
92    return CMS_flag_is_set(CMS_vm_has_token);
93  }
94  static bool cms_thread_has_cms_token() {
95    return CMS_flag_is_set(CMS_cms_has_token);
96  }
97  static bool vm_thread_wants_cms_token() {
98    return CMS_flag_is_set(CMS_vm_wants_token);
99  }
100  static bool cms_thread_wants_cms_token() {
101    return CMS_flag_is_set(CMS_cms_wants_token);
102  }
103
104  // Wait on CMS lock until the next synchronous GC
105  // or given timeout, whichever is earlier. A timeout value
106  // of 0 indicates that there is no upper bound on the wait time.
107  // A concurrent full gc request terminates the wait.
108  void wait_on_cms_lock(long t_millis);
109
110  // Wait on CMS lock until the next synchronous GC
111  // or given timeout, whichever is earlier. A timeout value
112  // of 0 indicates that there is no upper bound on the wait time.
113  // A concurrent full gc request terminates the wait.
114  void wait_on_cms_lock_for_scavenge(long t_millis);
115
116  // The CMS thread will yield during the work portion of its cycle
117  // only when requested to.
118  // A synchronous request is used for young gen collections and
119  // for direct allocations.  The requesting thread increments
120  // _pending_yields at the beginning of an operation, and decrements
121  // _pending_yields when that operation is completed.
122  // In turn, the CMS thread yields when _pending_yields is positive,
123  // and continues to yield until the value reverts to 0.
124
125  static void increment_pending_yields()   {
126    Atomic::inc(&_pending_yields);
127    assert(_pending_yields >= 0, "can't be negative");
128  }
129  static void decrement_pending_yields()   {
130    Atomic::dec(&_pending_yields);
131    assert(_pending_yields >= 0, "can't be negative");
132  }
133  static bool should_yield()   { return _pending_yields > 0; }
134};
135
136// For scoped increment/decrement of (synchronous) yield requests
137class CMSSynchronousYieldRequest: public StackObj {
138 public:
139  CMSSynchronousYieldRequest() {
140    ConcurrentMarkSweepThread::increment_pending_yields();
141  }
142  ~CMSSynchronousYieldRequest() {
143    ConcurrentMarkSweepThread::decrement_pending_yields();
144  }
145};
146
147// Used to emit a warning in case of unexpectedly excessive
148// looping (in "apparently endless loops") in CMS code.
149class CMSLoopCountWarn: public StackObj {
150 private:
151  const char* _src;
152  const char* _msg;
153  const intx  _threshold;
154  intx        _ticks;
155
156 public:
157  inline CMSLoopCountWarn(const char* src, const char* msg,
158                          const intx threshold) :
159    _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
160
161  inline void tick() {
162    _ticks++;
163    if (CMSLoopWarn && _ticks % _threshold == 0) {
164      log_warning(gc)("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
165    }
166  }
167};
168
169#endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
170