1 /* 2 * Copyright (c) 2001, 2014, 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. 22 * 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 static void print_all_on(outputStream* st); 98 static void print_all() { print_all_on(tty); } 99 100 // Returns the CMS Thread 101 static ConcurrentMarkSweepThread* cmst() { return _cmst; } 102 static CMSCollector* collector() { return _collector; } 103 104 // Create and start the CMS Thread, or stop it on shutdown 105 static ConcurrentMarkSweepThread* start(CMSCollector* collector); 106 static void stop(); 107 static bool should_terminate() { return _should_terminate; } 108 109 // Synchronization using CMS token 110 static void synchronize(bool is_cms_thread); 111 static void desynchronize(bool is_cms_thread); 112 static bool vm_thread_has_cms_token() { 113 return CMS_flag_is_set(CMS_vm_has_token); 114 } 115 static bool cms_thread_has_cms_token() { 116 return CMS_flag_is_set(CMS_cms_has_token); 117 } 118 static bool vm_thread_wants_cms_token() { 119 return CMS_flag_is_set(CMS_vm_wants_token); 120 } 121 static bool cms_thread_wants_cms_token() { 122 return CMS_flag_is_set(CMS_cms_wants_token); 123 } 124 125 // Wait on CMS lock until the next synchronous GC 126 // or given timeout, whichever is earlier. A timeout value 127 // of 0 indicates that there is no upper bound on the wait time. 128 // A concurrent full gc request terminates the wait. 129 void wait_on_cms_lock(long t_millis); 130 131 // Wait on CMS lock until the next synchronous GC 132 // or given timeout, whichever is earlier. A timeout value 133 // of 0 indicates that there is no upper bound on the wait time. 134 // A concurrent full gc request terminates the wait. 135 void wait_on_cms_lock_for_scavenge(long t_millis); 136 137 // The CMS thread will yield during the work portion of its cycle 138 // only when requested to. Both synchronous and asychronous requests 139 // are provided: 140 // (1) A synchronous request is used for young gen collections and 141 // for direct allocations. The requesting thread increments 142 // _pending_yields at the beginning of an operation, and decrements 143 // _pending_yields when that operation is completed. 144 // In turn, the CMS thread yields when _pending_yields is positive, 145 // and continues to yield until the value reverts to 0. 146 // (2) An asynchronous request, on the other hand, is used by iCMS 147 // for the stop_icms() operation. A single yield satisfies all of 148 // the outstanding asynch yield requests, of which there may 149 // occasionally be several in close succession. To accomplish 150 // this, an asynch-requesting thread atomically increments both 151 // _pending_yields and _pending_decrements. An asynchr requesting 152 // thread does not wait and "acknowledge" completion of an operation 153 // and deregister the request, like the synchronous version described 154 // above does. In turn, after yielding, the CMS thread decrements both 155 // _pending_yields and _pending_decrements by the value seen in 156 // _pending_decrements before the decrement. 157 // NOTE: The above scheme is isomorphic to having two request counters, 158 // one for async requests and one for sync requests, and for the CMS thread 159 // to check the sum of the two counters to decide whether it should yield 160 // and to clear only the async counter when it yields. However, it turns out 161 // to be more efficient for CMS code to just check a single counter 162 // _pending_yields that holds the sum (of both sync and async requests), and 163 // a second counter _pending_decrements that only holds the async requests, 164 // for greater efficiency, since in a typical CMS run, there are many more 165 // potential (i.e. static) yield points than there are actual 166 // (i.e. dynamic) yields because of requests, which are few and far between. 167 // 168 // Note that, while "_pending_yields >= _pending_decrements" is an invariant, 169 // we cannot easily test that invariant, since the counters are manipulated via 170 // atomic instructions without explicit locking and we cannot read 171 // the two counters atomically together: one suggestion is to 172 // use (for example) 16-bit counters so as to be able to read the 173 // two counters atomically even on 32-bit platforms. Notice that 174 // the second assert in acknowledge_yield_request() below does indeed 175 // check a form of the above invariant, albeit indirectly. 176 177 static void increment_pending_yields() { 178 Atomic::inc(&_pending_yields); 179 assert(_pending_yields >= 0, "can't be negative"); 180 } 181 static void decrement_pending_yields() { 182 Atomic::dec(&_pending_yields); 183 assert(_pending_yields >= 0, "can't be negative"); 184 } 185 static void asynchronous_yield_request() { 186 assert(CMSIncrementalMode, "Currently only used w/iCMS"); 187 increment_pending_yields(); 188 Atomic::inc(&_pending_decrements); 189 assert(_pending_decrements >= 0, "can't be negative"); 190 } 191 static void acknowledge_yield_request() { 192 jint decrement = _pending_decrements; 193 if (decrement > 0) { 194 assert(CMSIncrementalMode, "Currently only used w/iCMS"); 195 // Order important to preserve: _pending_yields >= _pending_decrements 196 Atomic::add(-decrement, &_pending_decrements); 197 Atomic::add(-decrement, &_pending_yields); 198 assert(_pending_decrements >= 0, "can't be negative"); 199 assert(_pending_yields >= 0, "can't be negative"); 200 } 201 } 202 static bool should_yield() { return _pending_yields > 0; } 203 204 // CMS incremental mode. 205 static void start_icms(); // notify thread to start a quantum of work 206 static void stop_icms(); // request thread to stop working 207 void icms_wait(); // if asked to stop, wait until notified to start 208 209 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It 210 // must also be enabled/disabled dynamically to allow foreground collections. 211 #define ICMS_ENABLING_ASSERT \ 212 assert((CMSIncrementalMode && _icms_disabled >= 0) || \ 213 (!CMSIncrementalMode && _icms_disabled <= 0), "Error") 214 215 static inline void enable_icms() { 216 ICMS_ENABLING_ASSERT; 217 Atomic::dec(&_icms_disabled); 218 } 219 static inline void disable_icms() { 220 ICMS_ENABLING_ASSERT; 221 Atomic::inc(&_icms_disabled); 222 } 223 static inline bool icms_is_disabled() { 224 ICMS_ENABLING_ASSERT; 225 return _icms_disabled > 0; 226 } 227 static inline bool icms_is_enabled() { 228 return !icms_is_disabled(); 229 } 230 }; 231 232 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) { 233 if (CMSTraceThreadState) { 234 char buf[128]; 235 TimeStamp& ts = gclog_or_tty->time_stamp(); 236 if (!ts.is_updated()) { 237 ts.update(); 238 } 239 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ", 240 ts.seconds(), desc); 241 buf[sizeof(buf) - 1] = '\0'; 242 gclog_or_tty->print("%s", buf); 243 } 244 } 245 246 // For scoped increment/decrement of (synchronous) yield requests 247 class CMSSynchronousYieldRequest: public StackObj { 248 public: 249 CMSSynchronousYieldRequest() { 250 ConcurrentMarkSweepThread::increment_pending_yields(); 251 } 252 ~CMSSynchronousYieldRequest() { 253 ConcurrentMarkSweepThread::decrement_pending_yields(); 254 } 255 }; 256 257 // Used to emit a warning in case of unexpectedly excessive 258 // looping (in "apparently endless loops") in CMS code. 259 class CMSLoopCountWarn: public StackObj { 260 private: 261 const char* _src; 262 const char* _msg; 263 const intx _threshold; 264 intx _ticks; 265 266 public: 267 inline CMSLoopCountWarn(const char* src, const char* msg, 268 const intx threshold) : 269 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } 270 271 inline void tick() { 272 _ticks++; 273 if (CMSLoopWarn && _ticks % _threshold == 0) { 274 warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg); 275 } 276 } 277 }; 278 279 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP