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 #ifdef TARGET_OS_FAMILY_linux
31 # include "thread_linux.inline.hpp"
32 #endif
33 #ifdef TARGET_OS_FAMILY_solaris
34 # include "thread_solaris.inline.hpp"
35 #endif
36 #ifdef TARGET_OS_FAMILY_windows
37 # include "thread_windows.inline.hpp"
38 #endif
39 #ifdef TARGET_OS_FAMILY_bsd
40 # include "thread_bsd.inline.hpp"
41 #endif
42
43 class ConcurrentMarkSweepGeneration;
44 class CMSCollector;
45
46 // The Concurrent Mark Sweep GC Thread
47 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
48 friend class VMStructs;
49 friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
50 friend class CMSCollector;
51 public:
52 virtual void run();
53
54 private:
55 static ConcurrentMarkSweepThread* _cmst;
56 static CMSCollector* _collector;
57 static SurrogateLockerThread* _slt;
58 static SurrogateLockerThread::SLT_msg_type _sltBuffer;
59 static Monitor* _sltMonitor;
60
61 static bool _should_terminate;
62
63 enum CMS_flag_type {
64 CMS_nil = NoBits,
65 CMS_cms_wants_token = nth_bit(0),
66 CMS_cms_has_token = nth_bit(1),
67 CMS_vm_wants_token = nth_bit(2),
68 CMS_vm_has_token = nth_bit(3)
69 };
70
71 static int _CMS_flag;
72
73 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
74 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
75 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
76 void sleepBeforeNextCycle();
77
78 // CMS thread should yield for a young gen collection, direct allocation,
79 // and iCMS activity.
80 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
81 static volatile jint _pending_yields;
82 static volatile jint _pending_decrements; // decrements to _pending_yields
83 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
84
85 // Tracing messages, enabled by CMSTraceThreadState.
86 static inline void trace_state(const char* desc);
87
88 static volatile int _icms_disabled; // a counter to track #iCMS disable & enable
89 static volatile bool _should_run; // iCMS may run
90 static volatile bool _should_stop; // iCMS should stop
91
92 // debugging
93 void verify_ok_to_terminate() const PRODUCT_RETURN;
94
95 public:
96 // Constructor
97 ConcurrentMarkSweepThread(CMSCollector* collector);
98
99 static void makeSurrogateLockerThread(TRAPS);
100 static SurrogateLockerThread* slt() { return _slt; }
101
102 // Tester
103 bool is_ConcurrentGC_thread() const { return true; }
104
105 static void threads_do(ThreadClosure* tc);
106
107 // Printing
108 void print_on(outputStream* st) const;
109 void print() const { print_on(tty); }
110 static void print_all_on(outputStream* st);
111 static void print_all() { print_all_on(tty); }
112
113 // Returns the CMS Thread
114 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
115 static CMSCollector* collector() { return _collector; }
116
117 // Create and start the CMS Thread, or stop it on shutdown
118 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
119 static void stop();
120 static bool should_terminate() { return _should_terminate; }
121
122 // Synchronization using CMS token
123 static void synchronize(bool is_cms_thread);
124 static void desynchronize(bool is_cms_thread);
125 static bool vm_thread_has_cms_token() {
126 return CMS_flag_is_set(CMS_vm_has_token);
127 }
128 static bool cms_thread_has_cms_token() {
129 return CMS_flag_is_set(CMS_cms_has_token);
130 }
131 static bool vm_thread_wants_cms_token() {
132 return CMS_flag_is_set(CMS_vm_wants_token);
133 }
134 static bool cms_thread_wants_cms_token() {
135 return CMS_flag_is_set(CMS_cms_wants_token);
136 }
137
138 // Wait on CMS lock until the next synchronous GC
139 // or given timeout, whichever is earlier. A timeout value
140 // of 0 indicates that there is no upper bound on the wait time.
141 // A concurrent full gc request terminates the wait.
142 void wait_on_cms_lock(long t_millis);
143
144 // The CMS thread will yield during the work portion of its cycle
145 // only when requested to. Both synchronous and asychronous requests
146 // are provided:
147 // (1) A synchronous request is used for young gen collections and
148 // for direct allocations. The requesting thread increments
149 // _pending_yields at the beginning of an operation, and decrements
150 // _pending_yields when that operation is completed.
151 // In turn, the CMS thread yields when _pending_yields is positive,
152 // and continues to yield until the value reverts to 0.
153 // (2) An asynchronous request, on the other hand, is used by iCMS
154 // for the stop_icms() operation. A single yield satisfies all of
155 // the outstanding asynch yield requests, of which there may
156 // occasionally be several in close succession. To accomplish
157 // this, an asynch-requesting thread atomically increments both
158 // _pending_yields and _pending_decrements. An asynchr requesting
159 // thread does not wait and "acknowledge" completion of an operation
160 // and deregister the request, like the synchronous version described
161 // above does. In turn, after yielding, the CMS thread decrements both
162 // _pending_yields and _pending_decrements by the value seen in
163 // _pending_decrements before the decrement.
164 // NOTE: The above scheme is isomorphic to having two request counters,
165 // one for async requests and one for sync requests, and for the CMS thread
166 // to check the sum of the two counters to decide whether it should yield
167 // and to clear only the async counter when it yields. However, it turns out
168 // to be more efficient for CMS code to just check a single counter
169 // _pending_yields that holds the sum (of both sync and async requests), and
170 // a second counter _pending_decrements that only holds the async requests,
171 // for greater efficiency, since in a typical CMS run, there are many more
172 // pontential (i.e. static) yield points than there are actual
173 // (i.e. dynamic) yields because of requests, which are few and far between.
174 //
175 // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
176 // we cannot easily test that invariant, since the counters are manipulated via
177 // atomic instructions without explicit locking and we cannot read
178 // the two counters atomically together: one suggestion is to
179 // use (for example) 16-bit counters so as to be able to read the
180 // two counters atomically even on 32-bit platforms. Notice that
181 // the second assert in acknowledge_yield_request() below does indeed
182 // check a form of the above invariant, albeit indirectly.
183
184 static void increment_pending_yields() {
185 Atomic::inc(&_pending_yields);
186 assert(_pending_yields >= 0, "can't be negative");
187 }
188 static void decrement_pending_yields() {
189 Atomic::dec(&_pending_yields);
190 assert(_pending_yields >= 0, "can't be negative");
191 }
192 static void asynchronous_yield_request() {
193 assert(CMSIncrementalMode, "Currently only used w/iCMS");
194 increment_pending_yields();
195 Atomic::inc(&_pending_decrements);
196 assert(_pending_decrements >= 0, "can't be negative");
197 }
198 static void acknowledge_yield_request() {
199 jint decrement = _pending_decrements;
200 if (decrement > 0) {
201 assert(CMSIncrementalMode, "Currently only used w/iCMS");
202 // Order important to preserve: _pending_yields >= _pending_decrements
203 Atomic::add(-decrement, &_pending_decrements);
204 Atomic::add(-decrement, &_pending_yields);
205 assert(_pending_decrements >= 0, "can't be negative");
206 assert(_pending_yields >= 0, "can't be negative");
207 }
208 }
209 static bool should_yield() { return _pending_yields > 0; }
210
211 // CMS incremental mode.
212 static void start_icms(); // notify thread to start a quantum of work
213 static void stop_icms(); // request thread to stop working
214 void icms_wait(); // if asked to stop, wait until notified to start
215
216 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
217 // must also be enabled/disabled dynamically to allow foreground collections.
218 #define ICMS_ENABLING_ASSERT \
219 assert((CMSIncrementalMode && _icms_disabled >= 0) || \
220 (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
221
222 static inline void enable_icms() {
223 ICMS_ENABLING_ASSERT;
224 Atomic::dec(&_icms_disabled);
225 }
226 static inline void disable_icms() {
227 ICMS_ENABLING_ASSERT;
228 Atomic::inc(&_icms_disabled);
229 }
230 static inline bool icms_is_disabled() {
231 ICMS_ENABLING_ASSERT;
232 return _icms_disabled > 0;
233 }
234 static inline bool icms_is_enabled() {
235 return !icms_is_disabled();
236 }
237 };
238
239 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
240 if (CMSTraceThreadState) {
241 char buf[128];
242 TimeStamp& ts = gclog_or_tty->time_stamp();
243 if (!ts.is_updated()) {
244 ts.update();
245 }
246 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
247 ts.seconds(), desc);
248 buf[sizeof(buf) - 1] = '\0';
249 gclog_or_tty->print(buf);
250 }
251 }
252
253 // For scoped increment/decrement of (synchronous) yield requests
254 class CMSSynchronousYieldRequest: public StackObj {
255 public:
256 CMSSynchronousYieldRequest() {
257 ConcurrentMarkSweepThread::increment_pending_yields();
258 }
259 ~CMSSynchronousYieldRequest() {
260 ConcurrentMarkSweepThread::decrement_pending_yields();
261 }
262 };
263
264 // Used to emit a warning in case of unexpectedly excessive
265 // looping (in "apparently endless loops") in CMS code.
266 class CMSLoopCountWarn: public StackObj {
267 private:
268 const char* _src;
269 const char* _msg;
270 const intx _threshold;
271 intx _ticks;
272
273 public:
274 inline CMSLoopCountWarn(const char* src, const char* msg,
275 const intx threshold) :
276 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
277
278 inline void tick() {
279 _ticks++;
280 if (CMSLoopWarn && _ticks % _threshold == 0) {
281 warning("%s has looped %d times %s", _src, _ticks, _msg);
282 }
283 }
284 };
285
286 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP