1 /*
   2  * Copyright (c) 2001, 2012, 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 #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     st->cr();
 234   }
 235   if (_collector != NULL) {
 236     AbstractWorkGang* gang = _collector->conc_workers();
 237     if (gang != NULL) {
 238       gang->print_worker_threads_on(st);
 239     }
 240   }
 241 }
 242 
 243 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
 244   assert(UseConcMarkSweepGC, "just checking");
 245 
 246   MutexLockerEx x(CGC_lock,
 247                   Mutex::_no_safepoint_check_flag);
 248   if (!is_cms_thread) {
 249     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 250     CMSSynchronousYieldRequest yr;
 251     while (CMS_flag_is_set(CMS_cms_has_token)) {
 252       // indicate that we want to get the token
 253       set_CMS_flag(CMS_vm_wants_token);
 254       CGC_lock->wait(true);
 255     }
 256     // claim the token and proceed
 257     clear_CMS_flag(CMS_vm_wants_token);
 258     set_CMS_flag(CMS_vm_has_token);
 259   } else {
 260     assert(Thread::current()->is_ConcurrentGC_thread(),
 261            "Not a CMS thread");
 262     // The following barrier assumes there's only one CMS thread.
 263     // This will need to be modified is there are more CMS threads than one.
 264     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
 265       set_CMS_flag(CMS_cms_wants_token);
 266       CGC_lock->wait(true);
 267     }
 268     // claim the token
 269     clear_CMS_flag(CMS_cms_wants_token);
 270     set_CMS_flag(CMS_cms_has_token);
 271   }
 272 }
 273 
 274 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
 275   assert(UseConcMarkSweepGC, "just checking");
 276 
 277   MutexLockerEx x(CGC_lock,
 278                   Mutex::_no_safepoint_check_flag);
 279   if (!is_cms_thread) {
 280     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 281     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
 282     clear_CMS_flag(CMS_vm_has_token);
 283     if (CMS_flag_is_set(CMS_cms_wants_token)) {
 284       // wake-up a waiting CMS thread
 285       CGC_lock->notify();
 286     }
 287     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
 288            "Should have been cleared");
 289   } else {
 290     assert(Thread::current()->is_ConcurrentGC_thread(),
 291            "Not a CMS thread");
 292     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
 293     clear_CMS_flag(CMS_cms_has_token);
 294     if (CMS_flag_is_set(CMS_vm_wants_token)) {
 295       // wake-up a waiting VM thread
 296       CGC_lock->notify();
 297     }
 298     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 299            "Should have been cleared");
 300   }
 301 }
 302 
 303 // Wait until any cms_lock event
 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 // Wait until the next synchronous GC, a concurrent full gc request,
 318 // or a timeout, whichever is earlier.
 319 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
 320   // Wait time in millis or 0 value representing infinite wait for a scavenge
 321   assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
 322 
 323   GenCollectedHeap* gch = GenCollectedHeap::heap();
 324   double start_time_secs = os::elapsedTime();
 325   double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
 326 
 327   // Total collections count before waiting loop
 328   unsigned int before_count;
 329   {
 330     MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 331     before_count = gch->total_collections();
 332   }
 333 
 334   unsigned int loop_count = 0;
 335 
 336   while(!_should_terminate) {
 337     double now_time = os::elapsedTime();
 338     long wait_time_millis;
 339 
 340     if(t_millis != 0) {
 341       // New wait limit
 342       wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
 343       if(wait_time_millis <= 0) {
 344         // Wait time is over
 345         break;
 346       }
 347     } else {
 348       // No wait limit, wait if necessary forever
 349       wait_time_millis = 0;
 350     }
 351 
 352     // Wait until the next event or the remaining timeout
 353     {
 354       MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 355 
 356       if (_should_terminate || _collector->_full_gc_requested) {
 357         return;
 358       }
 359       set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 360       assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
 361       CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
 362       clear_CMS_flag(CMS_cms_wants_token);
 363       assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 364              "Should not be set");
 365     }
 366 
 367     // Extra wait time check before entering the heap lock to get the collection count
 368     if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
 369       // Wait time is over
 370       break;
 371     }
 372 
 373     // Total collections count after the event
 374     unsigned int after_count;
 375     {
 376       MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 377       after_count = gch->total_collections();
 378     }
 379 
 380     if(before_count != after_count) {
 381       // There was a collection - success
 382       break;
 383     }
 384 
 385     // Too many loops warning
 386     if(++loop_count == 0) {
 387       warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
 388     }
 389   }
 390 }
 391 
 392 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
 393   while (!_should_terminate) {
 394     if (CMSIncrementalMode) {
 395       icms_wait();
 396       if(CMSWaitDuration >= 0) {
 397         // Wait until the next synchronous GC, a concurrent full gc
 398         // request or a timeout, whichever is earlier.
 399         wait_on_cms_lock_for_scavenge(CMSWaitDuration);
 400       }
 401       return;
 402     } else {
 403       if(CMSWaitDuration >= 0) {
 404         // Wait until the next synchronous GC, a concurrent full gc
 405         // request or a timeout, whichever is earlier.
 406         wait_on_cms_lock_for_scavenge(CMSWaitDuration);
 407       } else {
 408         // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
 409         wait_on_cms_lock(CMSCheckInterval);
 410       }
 411     }
 412     // Check if we should start a CMS collection cycle
 413     if (_collector->shouldConcurrentCollect()) {
 414       return;
 415     }
 416     // .. collection criterion not yet met, let's go back
 417     // and wait some more
 418   }
 419 }
 420 
 421 // Incremental CMS
 422 void ConcurrentMarkSweepThread::start_icms() {
 423   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 424   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 425   trace_state("start_icms");
 426   _should_run = true;
 427   iCMS_lock->notify_all();
 428 }
 429 
 430 void ConcurrentMarkSweepThread::stop_icms() {
 431   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 432   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 433   if (!_should_stop) {
 434     trace_state("stop_icms");
 435     _should_stop = true;
 436     _should_run = false;
 437     asynchronous_yield_request();
 438     iCMS_lock->notify_all();
 439   }
 440 }
 441 
 442 void ConcurrentMarkSweepThread::icms_wait() {
 443   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 444   if (_should_stop && icms_is_enabled()) {
 445     MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 446     trace_state("pause_icms");
 447     _collector->stats().stop_cms_timer();
 448     while(!_should_run && icms_is_enabled()) {
 449       iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
 450     }
 451     _collector->stats().start_cms_timer();
 452     _should_stop = false;
 453     trace_state("pause_icms end");
 454   }
 455 }
 456 
 457 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 458 // which is a non-JavaThread, can only be called by a JavaThread.
 459 // Currently this is done at vm creation time (post-vm-init) by the
 460 // main/Primordial (Java)Thread.
 461 // XXX Consider changing this in the future to allow the CMS thread
 462 // itself to create this thread?
 463 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
 464   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
 465   assert(_slt == NULL, "SLT already created");
 466   _slt = SurrogateLockerThread::make(THREAD);
 467 }