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. 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 #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. 139 void wait_on_cms_lock(long t); // milliseconds 140 141 // The CMS thread will yield during the work portion of its cycle 142 // only when requested to. Both synchronous and asychronous requests 143 // are provided: 144 // (1) A synchronous request is used for young gen collections and 145 // for direct allocations. The requesting thread increments 146 // _pending_yields at the beginning of an operation, and decrements 147 // _pending_yields when that operation is completed. 148 // In turn, the CMS thread yields when _pending_yields is positive, 149 // and continues to yield until the value reverts to 0. 150 // (2) An asynchronous request, on the other hand, is used by iCMS 151 // for the stop_icms() operation. A single yield satisfies all of 152 // the outstanding asynch yield requests, of which there may 153 // occasionally be several in close succession. To accomplish 154 // this, an asynch-requesting thread atomically increments both 155 // _pending_yields and _pending_decrements. An asynchr requesting 156 // thread does not wait and "acknowledge" completion of an operation 157 // and deregister the request, like the synchronous version described 158 // above does. In turn, after yielding, the CMS thread decrements both 159 // _pending_yields and _pending_decrements by the value seen in 160 // _pending_decrements before the decrement. 161 // NOTE: The above scheme is isomorphic to having two request counters, 162 // one for async requests and one for sync requests, and for the CMS thread 163 // to check the sum of the two counters to decide whether it should yield 164 // and to clear only the async counter when it yields. However, it turns out 165 // to be more efficient for CMS code to just check a single counter 166 // _pending_yields that holds the sum (of both sync and async requests), and 167 // a second counter _pending_decrements that only holds the async requests, 168 // for greater efficiency, since in a typical CMS run, there are many more 169 // pontential (i.e. static) yield points than there are actual 170 // (i.e. dynamic) yields because of requests, which are few and far between. 171 // 172 // Note that, while "_pending_yields >= _pending_decrements" is an invariant, 173 // we cannot easily test that invariant, since the counters are manipulated via 174 // atomic instructions without explicit locking and we cannot read 175 // the two counters atomically together: one suggestion is to 176 // use (for example) 16-bit counters so as to be able to read the 177 // two counters atomically even on 32-bit platforms. Notice that 178 // the second assert in acknowledge_yield_request() below does indeed 179 // check a form of the above invariant, albeit indirectly. 180 181 static void increment_pending_yields() { 182 Atomic::inc(&_pending_yields); 183 assert(_pending_yields >= 0, "can't be negative"); 184 } 185 static void decrement_pending_yields() { 186 Atomic::dec(&_pending_yields); 187 assert(_pending_yields >= 0, "can't be negative"); 188 } 189 static void asynchronous_yield_request() { 190 assert(CMSIncrementalMode, "Currently only used w/iCMS"); 191 increment_pending_yields(); 192 Atomic::inc(&_pending_decrements); 193 assert(_pending_decrements >= 0, "can't be negative"); 194 } 195 static void acknowledge_yield_request() { 196 jint decrement = _pending_decrements; 197 if (decrement > 0) { 198 assert(CMSIncrementalMode, "Currently only used w/iCMS"); 199 // Order important to preserve: _pending_yields >= _pending_decrements 200 Atomic::add(-decrement, &_pending_decrements); 201 Atomic::add(-decrement, &_pending_yields); 202 assert(_pending_decrements >= 0, "can't be negative"); 203 assert(_pending_yields >= 0, "can't be negative"); 204 } 205 } 206 static bool should_yield() { return _pending_yields > 0; } 207 208 // CMS incremental mode. 209 static void start_icms(); // notify thread to start a quantum of work 210 static void stop_icms(); // request thread to stop working 211 void icms_wait(); // if asked to stop, wait until notified to start 212 213 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It 214 // must also be enabled/disabled dynamically to allow foreground collections. 215 static inline void enable_icms() { _icms_enabled = true; } 216 static inline void disable_icms() { _icms_enabled = false; } 217 static inline void set_icms_enabled(bool val) { _icms_enabled = val; } 218 static inline bool icms_enabled() { return _icms_enabled; } 219 }; 220 221 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) { 222 if (CMSTraceThreadState) { 223 char buf[128]; 224 TimeStamp& ts = gclog_or_tty->time_stamp(); 225 if (!ts.is_updated()) { 226 ts.update(); 227 } 228 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ", 229 ts.seconds(), desc); 230 buf[sizeof(buf) - 1] = '\0'; 231 gclog_or_tty->print(buf); 232 } 233 } 234 235 // For scoped increment/decrement of (synchronous) yield requests 236 class CMSSynchronousYieldRequest: public StackObj { 237 public: 238 CMSSynchronousYieldRequest() { 239 ConcurrentMarkSweepThread::increment_pending_yields(); 240 } 241 ~CMSSynchronousYieldRequest() { 242 ConcurrentMarkSweepThread::decrement_pending_yields(); 243 } 244 }; 245 246 // Used to emit a warning in case of unexpectedly excessive 247 // looping (in "apparently endless loops") in CMS code. 248 class CMSLoopCountWarn: public StackObj { 249 private: 250 const char* _src; 251 const char* _msg; 252 const intx _threshold; 253 intx _ticks; 254 255 public: 256 inline CMSLoopCountWarn(const char* src, const char* msg, 257 const intx threshold) : 258 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } 259 260 inline void tick() { 261 _ticks++; 262 if (CMSLoopWarn && _ticks % _threshold == 0) { 263 warning("%s has looped %d times %s", _src, _ticks, _msg); 264 } 265 } 266 }; 267 268 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP