1 /*
2 * Copyright (c) 2001, 2011, 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.
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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, direct allocation,
68 // and iCMS activity.
69 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
70 static volatile jint _pending_yields;
71 static volatile jint _pending_decrements; // decrements to _pending_yields
72 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
73
74 // Tracing messages, enabled by CMSTraceThreadState.
75 static inline void trace_state(const char* desc);
76
77 static volatile int _icms_disabled; // a counter to track #iCMS disable & enable
78 static volatile bool _should_run; // iCMS may run
79 static volatile bool _should_stop; // iCMS should stop
80
81 // debugging
82 void verify_ok_to_terminate() const PRODUCT_RETURN;
83
84 public:
85 // Constructor
86 ConcurrentMarkSweepThread(CMSCollector* collector);
87
88 static void makeSurrogateLockerThread(TRAPS);
89 static SurrogateLockerThread* slt() { return _slt; }
90
91 // Tester
92 bool is_ConcurrentGC_thread() const { return true; }
93
94 static void threads_do(ThreadClosure* tc);
95
96 // Printing
97 void print_on(outputStream* st) const;
98 void print() const { print_on(tty); }
99 static void print_all_on(outputStream* st);
100 static void print_all() { print_all_on(tty); }
101
102 // Returns the CMS Thread
103 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
104 static CMSCollector* collector() { return _collector; }
105
106 // Create and start the CMS Thread, or stop it on shutdown
107 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
108 static void stop();
109 static bool should_terminate() { return _should_terminate; }
110
111 // Synchronization using CMS token
112 static void synchronize(bool is_cms_thread);
113 static void desynchronize(bool is_cms_thread);
114 static bool vm_thread_has_cms_token() {
115 return CMS_flag_is_set(CMS_vm_has_token);
116 }
117 static bool cms_thread_has_cms_token() {
118 return CMS_flag_is_set(CMS_cms_has_token);
119 }
120 static bool vm_thread_wants_cms_token() {
121 return CMS_flag_is_set(CMS_vm_wants_token);
122 }
123 static bool cms_thread_wants_cms_token() {
124 return CMS_flag_is_set(CMS_cms_wants_token);
125 }
126
127 // Wait on CMS lock until the next synchronous GC
128 // or given timeout, whichever is earlier. A timeout value
129 // of 0 indicates that there is no upper bound on the wait time.
130 // A concurrent full gc request terminates the wait.
131 void wait_on_cms_lock(long t_millis);
132
133 // Wait on CMS lock until the next synchronous GC
134 // or given timeout, whichever is earlier. A timeout value
135 // of 0 indicates that there is no upper bound on the wait time.
136 // A concurrent full gc request terminates the wait.
137 void wait_on_cms_lock_for_scavenge(long t_millis);
138
139 // The CMS thread will yield during the work portion of its cycle
140 // only when requested to. Both synchronous and asychronous requests
141 // are provided:
142 // (1) A synchronous request is used for young gen collections and
143 // for direct allocations. The requesting thread increments
144 // _pending_yields at the beginning of an operation, and decrements
145 // _pending_yields when that operation is completed.
146 // In turn, the CMS thread yields when _pending_yields is positive,
147 // and continues to yield until the value reverts to 0.
148 // (2) An asynchronous request, on the other hand, is used by iCMS
149 // for the stop_icms() operation. A single yield satisfies all of
150 // the outstanding asynch yield requests, of which there may
151 // occasionally be several in close succession. To accomplish
152 // this, an asynch-requesting thread atomically increments both
153 // _pending_yields and _pending_decrements. An asynchr requesting
154 // thread does not wait and "acknowledge" completion of an operation
155 // and deregister the request, like the synchronous version described
156 // above does. In turn, after yielding, the CMS thread decrements both
157 // _pending_yields and _pending_decrements by the value seen in
158 // _pending_decrements before the decrement.
159 // NOTE: The above scheme is isomorphic to having two request counters,
160 // one for async requests and one for sync requests, and for the CMS thread
161 // to check the sum of the two counters to decide whether it should yield
162 // and to clear only the async counter when it yields. However, it turns out
163 // to be more efficient for CMS code to just check a single counter
164 // _pending_yields that holds the sum (of both sync and async requests), and
165 // a second counter _pending_decrements that only holds the async requests,
166 // for greater efficiency, since in a typical CMS run, there are many more
167 // pontential (i.e. static) yield points than there are actual
168 // (i.e. dynamic) yields because of requests, which are few and far between.
169 //
170 // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
171 // we cannot easily test that invariant, since the counters are manipulated via
172 // atomic instructions without explicit locking and we cannot read
173 // the two counters atomically together: one suggestion is to
174 // use (for example) 16-bit counters so as to be able to read the
175 // two counters atomically even on 32-bit platforms. Notice that
176 // the second assert in acknowledge_yield_request() below does indeed
177 // check a form of the above invariant, albeit indirectly.
178
179 static void increment_pending_yields() {
180 Atomic::inc(&_pending_yields);
181 assert(_pending_yields >= 0, "can't be negative");
182 }
183 static void decrement_pending_yields() {
184 Atomic::dec(&_pending_yields);
185 assert(_pending_yields >= 0, "can't be negative");
186 }
187 static void asynchronous_yield_request() {
188 assert(CMSIncrementalMode, "Currently only used w/iCMS");
189 increment_pending_yields();
190 Atomic::inc(&_pending_decrements);
191 assert(_pending_decrements >= 0, "can't be negative");
192 }
193 static void acknowledge_yield_request() {
194 jint decrement = _pending_decrements;
195 if (decrement > 0) {
196 assert(CMSIncrementalMode, "Currently only used w/iCMS");
197 // Order important to preserve: _pending_yields >= _pending_decrements
198 Atomic::add(-decrement, &_pending_decrements);
199 Atomic::add(-decrement, &_pending_yields);
200 assert(_pending_decrements >= 0, "can't be negative");
201 assert(_pending_yields >= 0, "can't be negative");
202 }
203 }
204 static bool should_yield() { return _pending_yields > 0; }
205
206 // CMS incremental mode.
207 static void start_icms(); // notify thread to start a quantum of work
208 static void stop_icms(); // request thread to stop working
209 void icms_wait(); // if asked to stop, wait until notified to start
210
211 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
212 // must also be enabled/disabled dynamically to allow foreground collections.
213 #define ICMS_ENABLING_ASSERT \
214 assert((CMSIncrementalMode && _icms_disabled >= 0) || \
215 (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
216
217 static inline void enable_icms() {
218 ICMS_ENABLING_ASSERT;
219 Atomic::dec(&_icms_disabled);
220 }
221 static inline void disable_icms() {
222 ICMS_ENABLING_ASSERT;
223 Atomic::inc(&_icms_disabled);
224 }
225 static inline bool icms_is_disabled() {
226 ICMS_ENABLING_ASSERT;
227 return _icms_disabled > 0;
228 }
229 static inline bool icms_is_enabled() {
230 return !icms_is_disabled();
231 }
232 };
233
234 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
235 if (CMSTraceThreadState) {
236 char buf[128];
237 TimeStamp& ts = gclog_or_tty->time_stamp();
238 if (!ts.is_updated()) {
239 ts.update();
240 }
241 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
242 ts.seconds(), desc);
243 buf[sizeof(buf) - 1] = '\0';
244 gclog_or_tty->print(buf);
245 }
246 }
247
248 // For scoped increment/decrement of (synchronous) yield requests
249 class CMSSynchronousYieldRequest: public StackObj {
250 public:
251 CMSSynchronousYieldRequest() {
252 ConcurrentMarkSweepThread::increment_pending_yields();
253 }
254 ~CMSSynchronousYieldRequest() {
255 ConcurrentMarkSweepThread::decrement_pending_yields();
256 }
257 };
258
259 // Used to emit a warning in case of unexpectedly excessive
260 // looping (in "apparently endless loops") in CMS code.
261 class CMSLoopCountWarn: public StackObj {
262 private:
263 const char* _src;
264 const char* _msg;
265 const intx _threshold;
266 intx _ticks;
267
268 public:
269 inline CMSLoopCountWarn(const char* src, const char* msg,
270 const intx threshold) :
271 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
272
273 inline void tick() {
274 _ticks++;
275 if (CMSLoopWarn && _ticks % _threshold == 0) {
276 warning("%s has looped %d times %s", _src, _ticks, _msg);
277 }
278 }
279 };
280
281 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP