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 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 static void threads_do(ThreadClosure* tc);
83
84 // Printing
85 static void print_all_on(outputStream* st);
86 static void print_all() { print_all_on(tty); }
87
88 // Returns the CMS Thread
89 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
90 static CMSCollector* collector() { return _collector; }
91
92 // Create and start the CMS Thread, or stop it on shutdown
93 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
94 static void stop_all();
95 static bool should_terminate() { return _should_terminate; }
96 // ConcurrentMarkSweepThread uses it's own termination protocol, not ConcurrentGCThread's:
97 virtual void stop() { ShouldNotReachHere(); }
98
99 // Synchronization using CMS token
100 static void synchronize(bool is_cms_thread);
101 static void desynchronize(bool is_cms_thread);
102 static bool vm_thread_has_cms_token() {
103 return CMS_flag_is_set(CMS_vm_has_token);
104 }
105 static bool cms_thread_has_cms_token() {
106 return CMS_flag_is_set(CMS_cms_has_token);
107 }
108 static bool vm_thread_wants_cms_token() {
109 return CMS_flag_is_set(CMS_vm_wants_token);
110 }
111 static bool cms_thread_wants_cms_token() {
112 return CMS_flag_is_set(CMS_cms_wants_token);
113 }
114
115 // Wait on CMS lock until the next synchronous GC
116 // or given timeout, whichever is earlier. A timeout value
117 // of 0 indicates that there is no upper bound on the wait time.
118 // A concurrent full gc request terminates the wait.
119 void wait_on_cms_lock(long t_millis);
120
121 // Wait on CMS lock until the next synchronous GC
122 // or given timeout, whichever is earlier. A timeout value
123 // of 0 indicates that there is no upper bound on the wait time.
124 // A concurrent full gc request terminates the wait.
125 void wait_on_cms_lock_for_scavenge(long t_millis);
126
127 // The CMS thread will yield during the work portion of its cycle
128 // only when requested to.
129 // A synchronous request is used for young gen collections and
130 // for direct allocations. The requesting thread increments
131 // _pending_yields at the beginning of an operation, and decrements
132 // _pending_yields when that operation is completed.
133 // In turn, the CMS thread yields when _pending_yields is positive,
134 // and continues to yield until the value reverts to 0.
135
136 static void increment_pending_yields() {
137 Atomic::inc(&_pending_yields);
138 assert(_pending_yields >= 0, "can't be negative");
139 }
140 static void decrement_pending_yields() {
141 Atomic::dec(&_pending_yields);
142 assert(_pending_yields >= 0, "can't be negative");
143 }
144 static bool should_yield() { return _pending_yields > 0; }
145 };
146
147 // For scoped increment/decrement of (synchronous) yield requests
148 class CMSSynchronousYieldRequest: public StackObj {
149 public:
150 CMSSynchronousYieldRequest() {
151 ConcurrentMarkSweepThread::increment_pending_yields();
152 }
153 ~CMSSynchronousYieldRequest() {
154 ConcurrentMarkSweepThread::decrement_pending_yields();
155 }
156 };
157
158 // Used to emit a warning in case of unexpectedly excessive
159 // looping (in "apparently endless loops") in CMS code.
160 class CMSLoopCountWarn: public StackObj {
161 private:
162 const char* _src;
163 const char* _msg;
164 const intx _threshold;
165 intx _ticks;
166
167 public:
168 inline CMSLoopCountWarn(const char* src, const char* msg,
169 const intx threshold) :
170 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
171
172 inline void tick() {
173 _ticks++;
174 if (CMSLoopWarn && _ticks % _threshold == 0) {
175 warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
176 }
177 }
178 };
179
180 #endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP