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annotate src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp @ 1562:dfe27f03244a
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date | Tue, 01 Jun 2010 11:48:33 -0700 |
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2 * Copyright (c) 2001, 2006, Oracle and/or its affiliates. All rights reserved. |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
0 | 22 * |
23 */ | |
24 | |
25 class ConcurrentMarkSweepGeneration; | |
26 class CMSCollector; | |
27 | |
28 // The Concurrent Mark Sweep GC Thread (could be several in the future). | |
29 class ConcurrentMarkSweepThread: public ConcurrentGCThread { | |
30 friend class VMStructs; | |
31 friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship | |
32 friend class CMSCollector; | |
33 public: | |
34 virtual void run(); | |
35 | |
36 private: | |
37 static ConcurrentMarkSweepThread* _cmst; | |
38 static CMSCollector* _collector; | |
39 static SurrogateLockerThread* _slt; | |
40 static SurrogateLockerThread::SLT_msg_type _sltBuffer; | |
41 static Monitor* _sltMonitor; | |
42 | |
43 ConcurrentMarkSweepThread* _next; | |
44 | |
45 static bool _should_terminate; | |
46 | |
47 enum CMS_flag_type { | |
48 CMS_nil = NoBits, | |
49 CMS_cms_wants_token = nth_bit(0), | |
50 CMS_cms_has_token = nth_bit(1), | |
51 CMS_vm_wants_token = nth_bit(2), | |
52 CMS_vm_has_token = nth_bit(3) | |
53 }; | |
54 | |
55 static int _CMS_flag; | |
56 | |
57 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; } | |
58 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; } | |
59 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; } | |
60 void sleepBeforeNextCycle(); | |
61 | |
62 // CMS thread should yield for a young gen collection, direct allocation, | |
63 // and iCMS activity. | |
64 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing | |
65 static volatile jint _pending_yields; | |
66 static volatile jint _pending_decrements; // decrements to _pending_yields | |
67 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing | |
68 | |
69 // Tracing messages, enabled by CMSTraceThreadState. | |
70 static inline void trace_state(const char* desc); | |
71 | |
72 static volatile bool _icms_enabled; // iCMS enabled? | |
73 static volatile bool _should_run; // iCMS may run | |
74 static volatile bool _should_stop; // iCMS should stop | |
75 | |
76 // debugging | |
77 void verify_ok_to_terminate() const PRODUCT_RETURN; | |
78 | |
79 public: | |
80 // Constructor | |
81 ConcurrentMarkSweepThread(CMSCollector* collector); | |
82 | |
83 static void makeSurrogateLockerThread(TRAPS); | |
84 static SurrogateLockerThread* slt() { return _slt; } | |
85 | |
86 // Tester | |
87 bool is_ConcurrentGC_thread() const { return true; } | |
88 | |
89 static void threads_do(ThreadClosure* tc); | |
90 | |
91 // Printing | |
92 void print_on(outputStream* st) const; | |
93 void print() const { print_on(tty); } | |
94 static void print_all_on(outputStream* st); | |
95 static void print_all() { print_all_on(tty); } | |
96 | |
97 // Returns the CMS Thread | |
98 static ConcurrentMarkSweepThread* cmst() { return _cmst; } | |
99 static CMSCollector* collector() { return _collector; } | |
100 | |
101 // Create and start the CMS Thread, or stop it on shutdown | |
102 static ConcurrentMarkSweepThread* start(CMSCollector* collector); | |
103 static void stop(); | |
104 static bool should_terminate() { return _should_terminate; } | |
105 | |
106 // Synchronization using CMS token | |
107 static void synchronize(bool is_cms_thread); | |
108 static void desynchronize(bool is_cms_thread); | |
109 static bool vm_thread_has_cms_token() { | |
110 return CMS_flag_is_set(CMS_vm_has_token); | |
111 } | |
112 static bool cms_thread_has_cms_token() { | |
113 return CMS_flag_is_set(CMS_cms_has_token); | |
114 } | |
115 static bool vm_thread_wants_cms_token() { | |
116 return CMS_flag_is_set(CMS_vm_wants_token); | |
117 } | |
118 static bool cms_thread_wants_cms_token() { | |
119 return CMS_flag_is_set(CMS_cms_wants_token); | |
120 } | |
121 | |
122 // Wait on CMS lock until the next synchronous GC | |
123 // or given timeout, whichever is earlier. | |
124 void wait_on_cms_lock(long t); // milliseconds | |
125 | |
126 // The CMS thread will yield during the work portion of it's cycle | |
127 // only when requested to. Both synchronous and asychronous requests | |
128 // are provided. A synchronous request is used for young gen | |
129 // collections and direct allocations. The requesting thread increments | |
130 // pending_yields at the beginning of an operation, and decrements it when | |
131 // the operation is completed. The CMS thread yields when pending_yields | |
132 // is positive. An asynchronous request is used by iCMS in the stop_icms() | |
133 // operation. A single yield satisfies the outstanding asynch yield requests. | |
134 // The requesting thread increments both pending_yields and pending_decrements. | |
135 // After yielding, the CMS thread decrements both by the amount in | |
136 // pending_decrements. | |
137 // Note that, while "_pending_yields >= _pending_decrements" is an invariant, | |
138 // we cannot easily test that invariant, since the counters are manipulated via | |
139 // atomic instructions without explicit locking and we cannot read | |
140 // the two counters atomically together: one suggestion is to | |
141 // use (for example) 16-bit counters so as to be able to read the | |
142 // two counters atomically even on 32-bit platforms. Notice that | |
143 // the second assert in acknowledge_yield_request() does indeed | |
144 // check a form of the above invariant, albeit indirectly. | |
145 | |
146 static void increment_pending_yields() { | |
147 Atomic::inc(&_pending_yields); | |
148 assert(_pending_yields >= 0, "can't be negative"); | |
149 } | |
150 static void decrement_pending_yields() { | |
151 Atomic::dec(&_pending_yields); | |
152 assert(_pending_yields >= 0, "can't be negative"); | |
153 } | |
154 static void asynchronous_yield_request() { | |
155 increment_pending_yields(); | |
156 Atomic::inc(&_pending_decrements); | |
157 assert(_pending_decrements >= 0, "can't be negative"); | |
158 } | |
159 static void acknowledge_yield_request() { | |
160 jint decrement = _pending_decrements; | |
161 if (decrement > 0) { | |
162 // Order important to preserve: _pending_yields >= _pending_decrements | |
163 Atomic::add(-decrement, &_pending_decrements); | |
164 Atomic::add(-decrement, &_pending_yields); | |
165 assert(_pending_decrements >= 0, "can't be negative"); | |
166 assert(_pending_yields >= 0, "can't be negative"); | |
167 } | |
168 } | |
169 static bool should_yield() { return _pending_yields > 0; } | |
170 | |
171 // CMS incremental mode. | |
172 static void start_icms(); // notify thread to start a quantum of work | |
173 static void stop_icms(); // request thread to stop working | |
174 void icms_wait(); // if asked to stop, wait until notified to start | |
175 | |
176 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It | |
177 // must also be enabled/disabled dynamically to allow foreground collections. | |
178 static inline void enable_icms() { _icms_enabled = true; } | |
179 static inline void disable_icms() { _icms_enabled = false; } | |
180 static inline void set_icms_enabled(bool val) { _icms_enabled = val; } | |
181 static inline bool icms_enabled() { return _icms_enabled; } | |
182 }; | |
183 | |
184 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) { | |
185 if (CMSTraceThreadState) { | |
186 char buf[128]; | |
187 TimeStamp& ts = gclog_or_tty->time_stamp(); | |
188 if (!ts.is_updated()) { | |
189 ts.update(); | |
190 } | |
191 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ", | |
192 ts.seconds(), desc); | |
193 buf[sizeof(buf) - 1] = '\0'; | |
194 gclog_or_tty->print(buf); | |
195 } | |
196 } | |
197 | |
198 // For scoped increment/decrement of yield requests | |
199 class CMSSynchronousYieldRequest: public StackObj { | |
200 public: | |
201 CMSSynchronousYieldRequest() { | |
202 ConcurrentMarkSweepThread::increment_pending_yields(); | |
203 } | |
204 ~CMSSynchronousYieldRequest() { | |
205 ConcurrentMarkSweepThread::decrement_pending_yields(); | |
206 } | |
207 }; | |
208 | |
209 // Used to emit a warning in case of unexpectedly excessive | |
210 // looping (in "apparently endless loops") in CMS code. | |
211 class CMSLoopCountWarn: public StackObj { | |
212 private: | |
213 const char* _src; | |
214 const char* _msg; | |
215 const intx _threshold; | |
216 intx _ticks; | |
217 | |
218 public: | |
219 inline CMSLoopCountWarn(const char* src, const char* msg, | |
220 const intx threshold) : | |
221 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } | |
222 | |
223 inline void tick() { | |
224 _ticks++; | |
225 if (CMSLoopWarn && _ticks % _threshold == 0) { | |
226 warning("%s has looped %d times %s", _src, _ticks, _msg); | |
227 } | |
228 } | |
229 }; |