1 /*
2 * Copyright (c) 2001, 2010, 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
40 class ConcurrentMarkSweepGeneration;
41 class CMSCollector;
42
43 // The Concurrent Mark Sweep GC Thread (could be several in the future).
44 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
45 friend class VMStructs;
46 friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
47 friend class CMSCollector;
48 public:
49 virtual void run();
50
51 private:
52 static ConcurrentMarkSweepThread* _cmst;
53 static CMSCollector* _collector;
54 static SurrogateLockerThread* _slt;
55 static SurrogateLockerThread::SLT_msg_type _sltBuffer;
56 static Monitor* _sltMonitor;
57
58 ConcurrentMarkSweepThread* _next;
59
60 static bool _should_terminate;
61
62 enum CMS_flag_type {
63 CMS_nil = NoBits,
64 CMS_cms_wants_token = nth_bit(0),
65 CMS_cms_has_token = nth_bit(1),
66 CMS_vm_wants_token = nth_bit(2),
67 CMS_vm_has_token = nth_bit(3)
68 };
69
70 static int _CMS_flag;
71
72 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
73 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
74 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
75 void sleepBeforeNextCycle();
76
77 // CMS thread should yield for a young gen collection, direct allocation,
78 // and iCMS activity.
79 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
80 static volatile jint _pending_yields;
81 static volatile jint _pending_decrements; // decrements to _pending_yields
82 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
83
84 // Tracing messages, enabled by CMSTraceThreadState.
85 static inline void trace_state(const char* desc);
86
87 static volatile bool _icms_enabled; // iCMS enabled?
88 static volatile bool _should_run; // iCMS may run
89 static volatile bool _should_stop; // iCMS should stop
90
91 // debugging
92 void verify_ok_to_terminate() const PRODUCT_RETURN;
93
94 public:
95 // Constructor
96 ConcurrentMarkSweepThread(CMSCollector* collector);
97
98 static void makeSurrogateLockerThread(TRAPS);
99 static SurrogateLockerThread* slt() { return _slt; }
100
101 // Tester
102 bool is_ConcurrentGC_thread() const { return true; }
103
104 static void threads_do(ThreadClosure* tc);
105
106 // Printing
107 void print_on(outputStream* st) const;
108 void print() const { print_on(tty); }
109 static void print_all_on(outputStream* st);
110 static void print_all() { print_all_on(tty); }
111
112 // Returns the CMS Thread
113 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
114 static CMSCollector* collector() { return _collector; }
115
116 // Create and start the CMS Thread, or stop it on shutdown
117 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
118 static void stop();
119 static bool should_terminate() { return _should_terminate; }
120
121 // Synchronization using CMS token
122 static void synchronize(bool is_cms_thread);
123 static void desynchronize(bool is_cms_thread);
124 static bool vm_thread_has_cms_token() {
125 return CMS_flag_is_set(CMS_vm_has_token);
126 }
127 static bool cms_thread_has_cms_token() {
128 return CMS_flag_is_set(CMS_cms_has_token);
129 }
130 static bool vm_thread_wants_cms_token() {
131 return CMS_flag_is_set(CMS_vm_wants_token);
132 }
133 static bool cms_thread_wants_cms_token() {
134 return CMS_flag_is_set(CMS_cms_wants_token);
135 }
136
137 // Wait on CMS lock until the next synchronous GC
138 // or given timeout, whichever is earlier. A timeout value
139 // of 0 indicates that there is no upper bound on the wait time.
140 // A concurrent full gc request terminates the wait.
141 void wait_on_cms_lock(long t_millis);
142
143 // The CMS thread will yield during the work portion of its cycle
144 // only when requested to. Both synchronous and asychronous requests
145 // are provided:
146 // (1) A synchronous request is used for young gen collections and
147 // for direct allocations. The requesting thread increments
148 // _pending_yields at the beginning of an operation, and decrements
149 // _pending_yields when that operation is completed.
150 // In turn, the CMS thread yields when _pending_yields is positive,
151 // and continues to yield until the value reverts to 0.
152 // (2) An asynchronous request, on the other hand, is used by iCMS
153 // for the stop_icms() operation. A single yield satisfies all of
154 // the outstanding asynch yield requests, of which there may
155 // occasionally be several in close succession. To accomplish
156 // this, an asynch-requesting thread atomically increments both
157 // _pending_yields and _pending_decrements. An asynchr requesting
158 // thread does not wait and "acknowledge" completion of an operation
159 // and deregister the request, like the synchronous version described
160 // above does. In turn, after yielding, the CMS thread decrements both
161 // _pending_yields and _pending_decrements by the value seen in
162 // _pending_decrements before the decrement.
163 // NOTE: The above scheme is isomorphic to having two request counters,
164 // one for async requests and one for sync requests, and for the CMS thread
165 // to check the sum of the two counters to decide whether it should yield
166 // and to clear only the async counter when it yields. However, it turns out
167 // to be more efficient for CMS code to just check a single counter
168 // _pending_yields that holds the sum (of both sync and async requests), and
169 // a second counter _pending_decrements that only holds the async requests,
170 // for greater efficiency, since in a typical CMS run, there are many more
171 // pontential (i.e. static) yield points than there are actual
172 // (i.e. dynamic) yields because of requests, which are few and far between.
173 //
174 // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
175 // we cannot easily test that invariant, since the counters are manipulated via
176 // atomic instructions without explicit locking and we cannot read
177 // the two counters atomically together: one suggestion is to
178 // use (for example) 16-bit counters so as to be able to read the
179 // two counters atomically even on 32-bit platforms. Notice that
180 // the second assert in acknowledge_yield_request() below does indeed
181 // check a form of the above invariant, albeit indirectly.
182
183 static void increment_pending_yields() {
184 Atomic::inc(&_pending_yields);
185 assert(_pending_yields >= 0, "can't be negative");
186 }
187 static void decrement_pending_yields() {
188 Atomic::dec(&_pending_yields);
189 assert(_pending_yields >= 0, "can't be negative");
190 }
191 static void asynchronous_yield_request() {
192 assert(CMSIncrementalMode, "Currently only used w/iCMS");
193 increment_pending_yields();
194 Atomic::inc(&_pending_decrements);
195 assert(_pending_decrements >= 0, "can't be negative");
196 }
197 static void acknowledge_yield_request() {
198 jint decrement = _pending_decrements;
199 if (decrement > 0) {
200 assert(CMSIncrementalMode, "Currently only used w/iCMS");
201 // Order important to preserve: _pending_yields >= _pending_decrements
202 Atomic::add(-decrement, &_pending_decrements);
203 Atomic::add(-decrement, &_pending_yields);
204 assert(_pending_decrements >= 0, "can't be negative");
205 assert(_pending_yields >= 0, "can't be negative");
206 }
207 }
208 static bool should_yield() { return _pending_yields > 0; }
209
210 // CMS incremental mode.
211 static void start_icms(); // notify thread to start a quantum of work
212 static void stop_icms(); // request thread to stop working
213 void icms_wait(); // if asked to stop, wait until notified to start
214
215 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
216 // must also be enabled/disabled dynamically to allow foreground collections.
217 static inline void enable_icms() { _icms_enabled = true; }
218 static inline void disable_icms() { _icms_enabled = false; }
219 static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
220 static inline bool icms_enabled() { return _icms_enabled; }
221 };
222
223 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
224 if (CMSTraceThreadState) {
225 char buf[128];
226 TimeStamp& ts = gclog_or_tty->time_stamp();
227 if (!ts.is_updated()) {
228 ts.update();
229 }
230 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
231 ts.seconds(), desc);
232 buf[sizeof(buf) - 1] = '\0';
233 gclog_or_tty->print(buf);
234 }
235 }
236
237 // For scoped increment/decrement of (synchronous) yield requests
238 class CMSSynchronousYieldRequest: public StackObj {
239 public:
240 CMSSynchronousYieldRequest() {
241 ConcurrentMarkSweepThread::increment_pending_yields();
242 }
243 ~CMSSynchronousYieldRequest() {
244 ConcurrentMarkSweepThread::decrement_pending_yields();
245 }
246 };
247
248 // Used to emit a warning in case of unexpectedly excessive
249 // looping (in "apparently endless loops") in CMS code.
250 class CMSLoopCountWarn: public StackObj {
251 private:
252 const char* _src;
253 const char* _msg;
254 const intx _threshold;
255 intx _ticks;
256
257 public:
258 inline CMSLoopCountWarn(const char* src, const char* msg,
259 const intx threshold) :
260 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
261
262 inline void tick() {
263 _ticks++;
264 if (CMSLoopWarn && _ticks % _threshold == 0) {
265 warning("%s has looped %d times %s", _src, _ticks, _msg);
266 }
267 }
268 };
269
270 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP