1 /*
2 * Copyright (c) 2001, 2014, 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_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
27
28 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
29 #include "gc_implementation/shared/concurrentGCThread.hpp"
30 #include "runtime/thread.inline.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 public:
41 virtual void run();
42
43 private:
44 static ConcurrentMarkSweepThread* _cmst;
45 static CMSCollector* _collector;
46 static SurrogateLockerThread* _slt;
47 static SurrogateLockerThread::SLT_msg_type _sltBuffer;
48 static Monitor* _sltMonitor;
49
50 static bool _should_terminate;
51
52 enum CMS_flag_type {
53 CMS_nil = NoBits,
54 CMS_cms_wants_token = nth_bit(0),
55 CMS_cms_has_token = nth_bit(1),
56 CMS_vm_wants_token = nth_bit(2),
57 CMS_vm_has_token = nth_bit(3)
58 };
59
60 static int _CMS_flag;
61
62 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
63 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
64 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
65 void sleepBeforeNextCycle();
66
67 // CMS thread should yield for a young gen collection and direct allocations
68 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
69 static volatile jint _pending_yields;
70 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
71
72 // debugging
73 void verify_ok_to_terminate() const PRODUCT_RETURN;
74
75 public:
76 // Constructor
77 ConcurrentMarkSweepThread(CMSCollector* collector);
78
79 static void makeSurrogateLockerThread(TRAPS);
80 static SurrogateLockerThread* slt() { return _slt; }
81
82 // Tester
83 bool is_ConcurrentGC_thread() const { return true; }
84
85 static void threads_do(ThreadClosure* tc);
86
87 // Printing
88 static void print_all_on(outputStream* st);
89 static void print_all() { print_all_on(tty); }
90
91 // Returns the CMS Thread
92 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
93 static CMSCollector* collector() { return _collector; }
94
95 // Create and start the CMS Thread, or stop it on shutdown
96 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
97 static void stop();
98 static bool should_terminate() { return _should_terminate; }
99
100 // Synchronization using CMS token
101 static void synchronize(bool is_cms_thread);
102 static void desynchronize(bool is_cms_thread);
103 static bool vm_thread_has_cms_token() {
104 return CMS_flag_is_set(CMS_vm_has_token);
105 }
106 static bool cms_thread_has_cms_token() {
107 return CMS_flag_is_set(CMS_cms_has_token);
108 }
109 static bool vm_thread_wants_cms_token() {
110 return CMS_flag_is_set(CMS_vm_wants_token);
111 }
112 static bool cms_thread_wants_cms_token() {
113 return CMS_flag_is_set(CMS_cms_wants_token);
114 }
115
116 // Wait on CMS lock until the next synchronous GC
117 // or given timeout, whichever is earlier. A timeout value
118 // of 0 indicates that there is no upper bound on the wait time.
119 // A concurrent full gc request terminates the wait.
120 void wait_on_cms_lock(long t_millis);
121
122 // Wait on CMS lock until the next synchronous GC
123 // or given timeout, whichever is earlier. A timeout value
124 // of 0 indicates that there is no upper bound on the wait time.
125 // A concurrent full gc request terminates the wait.
126 void wait_on_cms_lock_for_scavenge(long t_millis);
127
128 // The CMS thread will yield during the work portion of its cycle
129 // only when requested to.
130 // A synchronous request is used for young gen collections and
131 // for direct allocations. The requesting thread increments
132 // _pending_yields at the beginning of an operation, and decrements
133 // _pending_yields when that operation is completed.
134 // In turn, the CMS thread yields when _pending_yields is positive,
135 // and continues to yield until the value reverts to 0.
136
137 static void increment_pending_yields() {
138 Atomic::inc(&_pending_yields);
139 assert(_pending_yields >= 0, "can't be negative");
140 }
141 static void decrement_pending_yields() {
142 Atomic::dec(&_pending_yields);
143 assert(_pending_yields >= 0, "can't be negative");
144 }
145 static bool should_yield() { return _pending_yields > 0; }
146 };
147
148 // For scoped increment/decrement of (synchronous) yield requests
149 class CMSSynchronousYieldRequest: public StackObj {
150 public:
151 CMSSynchronousYieldRequest() {
152 ConcurrentMarkSweepThread::increment_pending_yields();
153 }
154 ~CMSSynchronousYieldRequest() {
155 ConcurrentMarkSweepThread::decrement_pending_yields();
156 }
157 };
158
159 // Used to emit a warning in case of unexpectedly excessive
160 // looping (in "apparently endless loops") in CMS code.
161 class CMSLoopCountWarn: public StackObj {
162 private:
163 const char* _src;
164 const char* _msg;
165 const intx _threshold;
166 intx _ticks;
167
168 public:
169 inline CMSLoopCountWarn(const char* src, const char* msg,
170 const intx threshold) :
171 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
172
173 inline void tick() {
174 _ticks++;
175 if (CMSLoopWarn && _ticks % _threshold == 0) {
176 warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
177 }
178 }
179 };
180
181 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP