rev 4482 : 8013934: Garbage collection event for CMS has wrong cause for System.gc()

   1 /*
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   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.
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   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
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  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
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  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/systemDictionary.hpp"
  27 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  28 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  29 #include "memory/genCollectedHeap.hpp"
  30 #include "oops/instanceRefKlass.hpp"
  31 #include "oops/oop.inline.hpp"
  32 #include "runtime/init.hpp"
  33 #include "runtime/interfaceSupport.hpp"
  34 #include "runtime/java.hpp"
  35 #include "runtime/javaCalls.hpp"
  36 #include "runtime/mutexLocker.hpp"
  37 #include "runtime/os.hpp"
  38 #include "runtime/vmThread.hpp"
  39 
  40 // ======= Concurrent Mark Sweep Thread ========
  41 
  42 // The CMS thread is created when Concurrent Mark Sweep is used in the
  43 // older of two generations in a generational memory system.
  44 
  45 ConcurrentMarkSweepThread*
  46      ConcurrentMarkSweepThread::_cmst     = NULL;
  47 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
  48 bool ConcurrentMarkSweepThread::_should_terminate = false;
  49 int  ConcurrentMarkSweepThread::_CMS_flag         = CMS_nil;
  50 
  51 volatile jint ConcurrentMarkSweepThread::_pending_yields      = 0;
  52 volatile jint ConcurrentMarkSweepThread::_pending_decrements  = 0;
  53 
  54 volatile jint ConcurrentMarkSweepThread::_icms_disabled   = 0;
  55 volatile bool ConcurrentMarkSweepThread::_should_run     = false;
  56 // When icms is enabled, the icms thread is stopped until explicitly
  57 // started.
  58 volatile bool ConcurrentMarkSweepThread::_should_stop    = true;
  59 
  60 SurrogateLockerThread*
  61      ConcurrentMarkSweepThread::_slt = NULL;
  62 SurrogateLockerThread::SLT_msg_type
  63      ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
  64 Monitor*
  65      ConcurrentMarkSweepThread::_sltMonitor = NULL;
  66 
  67 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
  68   : ConcurrentGCThread() {
  69   assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
  70   assert(_cmst == NULL, "CMS thread already created");
  71   _cmst = this;
  72   assert(_collector == NULL, "Collector already set");
  73   _collector = collector;
  74 
  75   set_name("Concurrent Mark-Sweep GC Thread");
  76 
  77   if (os::create_thread(this, os::cgc_thread)) {
  78     // An old comment here said: "Priority should be just less
  79     // than that of VMThread".  Since the VMThread runs at
  80     // NearMaxPriority, the old comment was inaccurate, but
  81     // changing the default priority to NearMaxPriority-1
  82     // could change current behavior, so the default of
  83     // NearMaxPriority stays in place.
  84     //
  85     // Note that there's a possibility of the VMThread
  86     // starving if UseCriticalCMSThreadPriority is on.
  87     // That won't happen on Solaris for various reasons,
  88     // but may well happen on non-Solaris platforms.
  89     int native_prio;
  90     if (UseCriticalCMSThreadPriority) {
  91       native_prio = os::java_to_os_priority[CriticalPriority];
  92     } else {
  93       native_prio = os::java_to_os_priority[NearMaxPriority];
  94     }
  95     os::set_native_priority(this, native_prio);
  96 
  97     if (!DisableStartThread) {
  98       os::start_thread(this);
  99     }
 100   }
 101   _sltMonitor = SLT_lock;
 102   assert(!CMSIncrementalMode || icms_is_enabled(), "Error");
 103 }
 104 
 105 void ConcurrentMarkSweepThread::run() {
 106   assert(this == cmst(), "just checking");
 107 
 108   this->record_stack_base_and_size();
 109   this->initialize_thread_local_storage();
 110   this->set_active_handles(JNIHandleBlock::allocate_block());
 111   // From this time Thread::current() should be working.
 112   assert(this == Thread::current(), "just checking");
 113   if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
 114     warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
 115   }
 116   // Wait until Universe::is_fully_initialized()
 117   {
 118     CMSLoopCountWarn loopX("CMS::run", "waiting for "
 119                            "Universe::is_fully_initialized()", 2);
 120     MutexLockerEx x(CGC_lock, true);
 121     set_CMS_flag(CMS_cms_wants_token);
 122     // Wait until Universe is initialized and all initialization is completed.
 123     while (!is_init_completed() && !Universe::is_fully_initialized() &&
 124            !_should_terminate) {
 125       CGC_lock->wait(true, 200);
 126       loopX.tick();
 127     }
 128     // Wait until the surrogate locker thread that will do
 129     // pending list locking on our behalf has been created.
 130     // We cannot start the SLT thread ourselves since we need
 131     // to be a JavaThread to do so.
 132     CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
 133     while (_slt == NULL && !_should_terminate) {
 134       CGC_lock->wait(true, 200);
 135       loopY.tick();
 136     }
 137     clear_CMS_flag(CMS_cms_wants_token);
 138   }
 139 
 140   while (!_should_terminate) {
 141     sleepBeforeNextCycle();
 142     if (_should_terminate) break;
 143     _collector->collect_in_background(false);  // !clear_all_soft_refs


 144   }
 145   assert(_should_terminate, "just checking");
 146   // Check that the state of any protocol for synchronization
 147   // between background (CMS) and foreground collector is "clean"
 148   // (i.e. will not potentially block the foreground collector,
 149   // requiring action by us).
 150   verify_ok_to_terminate();
 151   // Signal that it is terminated
 152   {
 153     MutexLockerEx mu(Terminator_lock,
 154                      Mutex::_no_safepoint_check_flag);
 155     assert(_cmst == this, "Weird!");
 156     _cmst = NULL;
 157     Terminator_lock->notify();
 158   }
 159 
 160   // Thread destructor usually does this..
 161   ThreadLocalStorage::set_thread(NULL);
 162 }
 163 
 164 #ifndef PRODUCT
 165 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
 166   assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
 167            cms_thread_wants_cms_token()),
 168          "Must renounce all worldly possessions and desires for nirvana");
 169   _collector->verify_ok_to_terminate();
 170 }
 171 #endif
 172 
 173 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
 174 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
 175   if (!_should_terminate) {
 176     assert(cmst() == NULL, "start() called twice?");
 177     ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
 178     assert(cmst() == th, "Where did the just-created CMS thread go?");
 179     return th;
 180   }
 181   return NULL;
 182 }
 183 
 184 void ConcurrentMarkSweepThread::stop() {
 185   if (CMSIncrementalMode) {
 186     // Disable incremental mode and wake up the thread so it notices the change.
 187     disable_icms();
 188     start_icms();
 189   }
 190   // it is ok to take late safepoints here, if needed
 191   {
 192     MutexLockerEx x(Terminator_lock);
 193     _should_terminate = true;
 194   }
 195   { // Now post a notify on CGC_lock so as to nudge
 196     // CMS thread(s) that might be slumbering in
 197     // sleepBeforeNextCycle.
 198     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 199     CGC_lock->notify_all();
 200   }
 201   { // Now wait until (all) CMS thread(s) have exited
 202     MutexLockerEx x(Terminator_lock);
 203     while(cmst() != NULL) {
 204       Terminator_lock->wait();
 205     }
 206   }
 207 }
 208 
 209 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
 210   assert(tc != NULL, "Null ThreadClosure");
 211   if (_cmst != NULL) {
 212     tc->do_thread(_cmst);
 213   }
 214   assert(Universe::is_fully_initialized(),
 215          "Called too early, make sure heap is fully initialized");
 216   if (_collector != NULL) {
 217     AbstractWorkGang* gang = _collector->conc_workers();
 218     if (gang != NULL) {
 219       gang->threads_do(tc);
 220     }
 221   }
 222 }
 223 
 224 void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
 225   st->print("\"%s\" ", name());
 226   Thread::print_on(st);
 227   st->cr();
 228 }
 229 
 230 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
 231   if (_cmst != NULL) {
 232     _cmst->print_on(st);
 233   }
 234   if (_collector != NULL) {
 235     AbstractWorkGang* gang = _collector->conc_workers();
 236     if (gang != NULL) {
 237       gang->print_worker_threads_on(st);
 238     }
 239   }
 240 }
 241 
 242 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
 243   assert(UseConcMarkSweepGC, "just checking");
 244 
 245   MutexLockerEx x(CGC_lock,
 246                   Mutex::_no_safepoint_check_flag);
 247   if (!is_cms_thread) {
 248     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 249     CMSSynchronousYieldRequest yr;
 250     while (CMS_flag_is_set(CMS_cms_has_token)) {
 251       // indicate that we want to get the token
 252       set_CMS_flag(CMS_vm_wants_token);
 253       CGC_lock->wait(true);
 254     }
 255     // claim the token and proceed
 256     clear_CMS_flag(CMS_vm_wants_token);
 257     set_CMS_flag(CMS_vm_has_token);
 258   } else {
 259     assert(Thread::current()->is_ConcurrentGC_thread(),
 260            "Not a CMS thread");
 261     // The following barrier assumes there's only one CMS thread.
 262     // This will need to be modified is there are more CMS threads than one.
 263     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
 264       set_CMS_flag(CMS_cms_wants_token);
 265       CGC_lock->wait(true);
 266     }
 267     // claim the token
 268     clear_CMS_flag(CMS_cms_wants_token);
 269     set_CMS_flag(CMS_cms_has_token);
 270   }
 271 }
 272 
 273 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
 274   assert(UseConcMarkSweepGC, "just checking");
 275 
 276   MutexLockerEx x(CGC_lock,
 277                   Mutex::_no_safepoint_check_flag);
 278   if (!is_cms_thread) {
 279     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 280     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
 281     clear_CMS_flag(CMS_vm_has_token);
 282     if (CMS_flag_is_set(CMS_cms_wants_token)) {
 283       // wake-up a waiting CMS thread
 284       CGC_lock->notify();
 285     }
 286     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
 287            "Should have been cleared");
 288   } else {
 289     assert(Thread::current()->is_ConcurrentGC_thread(),
 290            "Not a CMS thread");
 291     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
 292     clear_CMS_flag(CMS_cms_has_token);
 293     if (CMS_flag_is_set(CMS_vm_wants_token)) {
 294       // wake-up a waiting VM thread
 295       CGC_lock->notify();
 296     }
 297     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 298            "Should have been cleared");
 299   }
 300 }
 301 
 302 // Wait until the next synchronous GC, a concurrent full gc request,
 303 // or a timeout, whichever is earlier.
 304 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
 305   MutexLockerEx x(CGC_lock,
 306                   Mutex::_no_safepoint_check_flag);
 307   if (_should_terminate || _collector->_full_gc_requested) {
 308     return;
 309   }
 310   set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 311   CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
 312   clear_CMS_flag(CMS_cms_wants_token);
 313   assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 314          "Should not be set");
 315 }
 316 
 317 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
 318   while (!_should_terminate) {
 319     if (CMSIncrementalMode) {
 320       icms_wait();
 321       return;
 322     } else {
 323       // Wait until the next synchronous GC, a concurrent full gc
 324       // request or a timeout, whichever is earlier.
 325       wait_on_cms_lock(CMSWaitDuration);
 326     }
 327     // Check if we should start a CMS collection cycle
 328     if (_collector->shouldConcurrentCollect()) {
 329       return;
 330     }
 331     // .. collection criterion not yet met, let's go back
 332     // and wait some more
 333   }
 334 }
 335 
 336 // Incremental CMS
 337 void ConcurrentMarkSweepThread::start_icms() {
 338   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 339   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 340   trace_state("start_icms");
 341   _should_run = true;
 342   iCMS_lock->notify_all();
 343 }
 344 
 345 void ConcurrentMarkSweepThread::stop_icms() {
 346   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 347   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 348   if (!_should_stop) {
 349     trace_state("stop_icms");
 350     _should_stop = true;
 351     _should_run = false;
 352     asynchronous_yield_request();
 353     iCMS_lock->notify_all();
 354   }
 355 }
 356 
 357 void ConcurrentMarkSweepThread::icms_wait() {
 358   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 359   if (_should_stop && icms_is_enabled()) {
 360     MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 361     trace_state("pause_icms");
 362     _collector->stats().stop_cms_timer();
 363     while(!_should_run && icms_is_enabled()) {
 364       iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
 365     }
 366     _collector->stats().start_cms_timer();
 367     _should_stop = false;
 368     trace_state("pause_icms end");
 369   }
 370 }
 371 
 372 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 373 // which is a non-JavaThread, can only be called by a JavaThread.
 374 // Currently this is done at vm creation time (post-vm-init) by the
 375 // main/Primordial (Java)Thread.
 376 // XXX Consider changing this in the future to allow the CMS thread
 377 // itself to create this thread?
 378 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
 379   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
 380   assert(_slt == NULL, "SLT already created");
 381   _slt = SurrogateLockerThread::make(THREAD);
 382 }
--- EOF ---