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.
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.
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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
32 class ConcurrentMarkSweepGeneration;
33 class CMSCollector;
34
35 // The Concurrent Mark Sweep GC Thread
36 class 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
137 class 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.
149 class 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