Mercurial > hg > truffle
annotate src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp @ 1837:c99c53f07c14
6692906: CMS: parallel concurrent marking may be prone to hanging or stalling mutators for periods of time
Summary: Inserted missing yield(check)s in closures used during the work-stealing phase of parallel concurrent marking, a missing synchronous yield-request in the cms perm gen allocation path, and a terminator-terminator for the offer_termination invocation that monitors the yield status of the concurrent marking task. Elaborated some documentation comments and made some task queue termination loop flags configurable at start-up to aid debugging in the field.
Reviewed-by: jmasa, johnc, poonam
author | ysr |
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date | Wed, 29 Sep 2010 16:17:02 -0700 |
parents | c18cbe5936b8 |
children | cd3ef3fd20dd |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved. |
0 | 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 * | |
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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 | |
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126 // The CMS thread will yield during the work portion of its cycle |
0 | 127 // only when requested to. Both synchronous and asychronous requests |
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128 // are provided: |
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129 // (1) A synchronous request is used for young gen collections and |
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130 // for direct allocations. The requesting thread increments |
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131 // _pending_yields at the beginning of an operation, and decrements |
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132 // _pending_yields when that operation is completed. |
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133 // In turn, the CMS thread yields when _pending_yields is positive, |
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134 // and continues to yield until the value reverts to 0. |
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135 // (2) An asynchronous request, on the other hand, is used by iCMS |
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136 // for the stop_icms() operation. A single yield satisfies all of |
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137 // the outstanding asynch yield requests, of which there may |
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138 // occasionally be several in close succession. To accomplish |
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139 // this, an asynch-requesting thread atomically increments both |
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140 // _pending_yields and _pending_decrements. An asynchr requesting |
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141 // thread does not wait and "acknowledge" completion of an operation |
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142 // and deregister the request, like the synchronous version described |
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143 // above does. In turn, after yielding, the CMS thread decrements both |
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144 // _pending_yields and _pending_decrements by the value seen in |
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145 // _pending_decrements before the decrement. |
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146 // NOTE: The above scheme is isomorphic to having two request counters, |
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147 // one for async requests and one for sync requests, and for the CMS thread |
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148 // to check the sum of the two counters to decide whether it should yield |
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149 // and to clear only the async counter when it yields. However, it turns out |
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150 // to be more efficient for CMS code to just check a single counter |
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151 // _pending_yields that holds the sum (of both sync and async requests), and |
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152 // a second counter _pending_decrements that only holds the async requests, |
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153 // for greater efficiency, since in a typical CMS run, there are many more |
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154 // pontential (i.e. static) yield points than there are actual |
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155 // (i.e. dynamic) yields because of requests, which are few and far between. |
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156 // |
0 | 157 // Note that, while "_pending_yields >= _pending_decrements" is an invariant, |
158 // we cannot easily test that invariant, since the counters are manipulated via | |
159 // atomic instructions without explicit locking and we cannot read | |
160 // the two counters atomically together: one suggestion is to | |
161 // use (for example) 16-bit counters so as to be able to read the | |
162 // two counters atomically even on 32-bit platforms. Notice that | |
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163 // the second assert in acknowledge_yield_request() below does indeed |
0 | 164 // check a form of the above invariant, albeit indirectly. |
165 | |
166 static void increment_pending_yields() { | |
167 Atomic::inc(&_pending_yields); | |
168 assert(_pending_yields >= 0, "can't be negative"); | |
169 } | |
170 static void decrement_pending_yields() { | |
171 Atomic::dec(&_pending_yields); | |
172 assert(_pending_yields >= 0, "can't be negative"); | |
173 } | |
174 static void asynchronous_yield_request() { | |
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175 assert(CMSIncrementalMode, "Currently only used w/iCMS"); |
0 | 176 increment_pending_yields(); |
177 Atomic::inc(&_pending_decrements); | |
178 assert(_pending_decrements >= 0, "can't be negative"); | |
179 } | |
180 static void acknowledge_yield_request() { | |
181 jint decrement = _pending_decrements; | |
182 if (decrement > 0) { | |
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183 assert(CMSIncrementalMode, "Currently only used w/iCMS"); |
0 | 184 // Order important to preserve: _pending_yields >= _pending_decrements |
185 Atomic::add(-decrement, &_pending_decrements); | |
186 Atomic::add(-decrement, &_pending_yields); | |
187 assert(_pending_decrements >= 0, "can't be negative"); | |
188 assert(_pending_yields >= 0, "can't be negative"); | |
189 } | |
190 } | |
191 static bool should_yield() { return _pending_yields > 0; } | |
192 | |
193 // CMS incremental mode. | |
194 static void start_icms(); // notify thread to start a quantum of work | |
195 static void stop_icms(); // request thread to stop working | |
196 void icms_wait(); // if asked to stop, wait until notified to start | |
197 | |
198 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It | |
199 // must also be enabled/disabled dynamically to allow foreground collections. | |
200 static inline void enable_icms() { _icms_enabled = true; } | |
201 static inline void disable_icms() { _icms_enabled = false; } | |
202 static inline void set_icms_enabled(bool val) { _icms_enabled = val; } | |
203 static inline bool icms_enabled() { return _icms_enabled; } | |
204 }; | |
205 | |
206 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) { | |
207 if (CMSTraceThreadState) { | |
208 char buf[128]; | |
209 TimeStamp& ts = gclog_or_tty->time_stamp(); | |
210 if (!ts.is_updated()) { | |
211 ts.update(); | |
212 } | |
213 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ", | |
214 ts.seconds(), desc); | |
215 buf[sizeof(buf) - 1] = '\0'; | |
216 gclog_or_tty->print(buf); | |
217 } | |
218 } | |
219 | |
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220 // For scoped increment/decrement of (synchronous) yield requests |
0 | 221 class CMSSynchronousYieldRequest: public StackObj { |
222 public: | |
223 CMSSynchronousYieldRequest() { | |
224 ConcurrentMarkSweepThread::increment_pending_yields(); | |
225 } | |
226 ~CMSSynchronousYieldRequest() { | |
227 ConcurrentMarkSweepThread::decrement_pending_yields(); | |
228 } | |
229 }; | |
230 | |
231 // Used to emit a warning in case of unexpectedly excessive | |
232 // looping (in "apparently endless loops") in CMS code. | |
233 class CMSLoopCountWarn: public StackObj { | |
234 private: | |
235 const char* _src; | |
236 const char* _msg; | |
237 const intx _threshold; | |
238 intx _ticks; | |
239 | |
240 public: | |
241 inline CMSLoopCountWarn(const char* src, const char* msg, | |
242 const intx threshold) : | |
243 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } | |
244 | |
245 inline void tick() { | |
246 _ticks++; | |
247 if (CMSLoopWarn && _ticks % _threshold == 0) { | |
248 warning("%s has looped %d times %s", _src, _ticks, _msg); | |
249 } | |
250 } | |
251 }; |