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.
22 *
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 static SurrogateLockerThread* _slt;
45 static SurrogateLockerThread::SLT_msg_type _sltBuffer;
46 static Monitor* _sltMonitor;
47
48 enum CMS_flag_type {
49 CMS_nil = NoBits,
50 CMS_cms_wants_token = nth_bit(0),
51 CMS_cms_has_token = nth_bit(1),
52 CMS_vm_wants_token = nth_bit(2),
53 CMS_vm_has_token = nth_bit(3)
54 };
55
56 static int _CMS_flag;
57
58 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
59 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
60 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
61 void sleepBeforeNextCycle();
62
63 // CMS thread should yield for a young gen collection and direct allocations
64 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
65 static volatile jint _pending_yields;
66 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
67
68 // debugging
69 void verify_ok_to_terminate() const PRODUCT_RETURN;
70
71 void run_service();
72 void stop_service();
73
74 public:
75 // Constructor
76 ConcurrentMarkSweepThread(CMSCollector* collector);
77
78 static void makeSurrogateLockerThread(TRAPS);
79 static SurrogateLockerThread* slt() { return _slt; }
80
81 static void threads_do(ThreadClosure* tc);
82
83 // Printing
84 static void print_all_on(outputStream* st);
85 static void print_all() { print_all_on(tty); }
86
87 // Returns the CMS Thread
88 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
89 static CMSCollector* collector() { return _collector; }
90
91 // Create and start the CMS Thread, or stop it on shutdown
92 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
93 static void stop_all();
94
95 // Synchronization using CMS token
96 static void synchronize(bool is_cms_thread);
97 static void desynchronize(bool is_cms_thread);
98 static bool vm_thread_has_cms_token() {
99 return CMS_flag_is_set(CMS_vm_has_token);
100 }
101 static bool cms_thread_has_cms_token() {
102 return CMS_flag_is_set(CMS_cms_has_token);
103 }
104 static bool vm_thread_wants_cms_token() {
105 return CMS_flag_is_set(CMS_vm_wants_token);
106 }
107 static bool cms_thread_wants_cms_token() {
108 return CMS_flag_is_set(CMS_cms_wants_token);
109 }
110
111 // Wait on CMS lock until the next synchronous GC
112 // or given timeout, whichever is earlier. A timeout value
113 // of 0 indicates that there is no upper bound on the wait time.
114 // A concurrent full gc request terminates the wait.
115 void wait_on_cms_lock(long t_millis);
116
117 // Wait on CMS lock until the next synchronous GC
118 // or given timeout, whichever is earlier. A timeout value
119 // of 0 indicates that there is no upper bound on the wait time.
120 // A concurrent full gc request terminates the wait.
121 void wait_on_cms_lock_for_scavenge(long t_millis);
122
123 // The CMS thread will yield during the work portion of its cycle
124 // only when requested to.
125 // A synchronous request is used for young gen collections and
126 // for direct allocations. The requesting thread increments
127 // _pending_yields at the beginning of an operation, and decrements
128 // _pending_yields when that operation is completed.
129 // In turn, the CMS thread yields when _pending_yields is positive,
130 // and continues to yield until the value reverts to 0.
131
132 static void increment_pending_yields() {
133 Atomic::inc(&_pending_yields);
134 assert(_pending_yields >= 0, "can't be negative");
135 }
136 static void decrement_pending_yields() {
137 Atomic::dec(&_pending_yields);
138 assert(_pending_yields >= 0, "can't be negative");
139 }
140 static bool should_yield() { return _pending_yields > 0; }
141 };
142
143 // For scoped increment/decrement of (synchronous) yield requests
144 class CMSSynchronousYieldRequest: public StackObj {
145 public:
146 CMSSynchronousYieldRequest() {
147 ConcurrentMarkSweepThread::increment_pending_yields();
148 }
149 ~CMSSynchronousYieldRequest() {
150 ConcurrentMarkSweepThread::decrement_pending_yields();
151 }
152 };
153
154 // Used to emit a warning in case of unexpectedly excessive
155 // looping (in "apparently endless loops") in CMS code.
156 class CMSLoopCountWarn: public StackObj {
157 private:
158 const char* _src;
159 const char* _msg;
160 const intx _threshold;
161 intx _ticks;
162
163 public:
164 inline CMSLoopCountWarn(const char* src, const char* msg,
165 const intx threshold) :
166 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
167
168 inline void tick() {
169 _ticks++;
170 if (CMSLoopWarn && _ticks % _threshold == 0) {
171 warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
172 }
173 }
174 };
175
176 #endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP