1 /*
   2  * Copyright (c) 2001, 2015, 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/cms/concurrentMarkSweepGeneration.inline.hpp"
  28 #include "gc/cms/concurrentMarkSweepThread.hpp"
  29 #include "gc/shared/gcId.hpp"
  30 #include "gc/shared/genCollectedHeap.hpp"
  31 #include "oops/instanceRefKlass.hpp"
  32 #include "oops/oop.inline.hpp"
  33 #include "runtime/init.hpp"
  34 #include "runtime/interfaceSupport.hpp"
  35 #include "runtime/java.hpp"
  36 #include "runtime/javaCalls.hpp"
  37 #include "runtime/mutexLocker.hpp"
  38 #include "runtime/os.hpp"
  39 #include "runtime/vmThread.hpp"
  40 
  41 // ======= Concurrent Mark Sweep Thread ========
  42 
  43 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::_cmst = NULL;
  44 CMSCollector* ConcurrentMarkSweepThread::_collector         = NULL;
  45 bool ConcurrentMarkSweepThread::_should_terminate           = false;
  46 int  ConcurrentMarkSweepThread::_CMS_flag                   = CMS_nil;
  47 
  48 volatile jint ConcurrentMarkSweepThread::_pending_yields    = 0;
  49 
  50 SurrogateLockerThread* ConcurrentMarkSweepThread::_slt      = NULL;
  51 SurrogateLockerThread::SLT_msg_type
  52      ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
  53 Monitor* ConcurrentMarkSweepThread::_sltMonitor             = NULL;
  54 
  55 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
  56   : ConcurrentGCThread() {
  57   assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
  58   assert(_cmst == NULL, "CMS thread already created");
  59   _cmst = this;
  60   assert(_collector == NULL, "Collector already set");
  61   _collector = collector;
  62 
  63   set_name("CMS Main Thread");
  64 
  65   if (os::create_thread(this, os::cgc_thread)) {
  66     // An old comment here said: "Priority should be just less
  67     // than that of VMThread".  Since the VMThread runs at
  68     // NearMaxPriority, the old comment was inaccurate, but
  69     // changing the default priority to NearMaxPriority-1
  70     // could change current behavior, so the default of
  71     // NearMaxPriority stays in place.
  72     //
  73     // Note that there's a possibility of the VMThread
  74     // starving if UseCriticalCMSThreadPriority is on.
  75     // That won't happen on Solaris for various reasons,
  76     // but may well happen on non-Solaris platforms.
  77     int native_prio;
  78     if (UseCriticalCMSThreadPriority) {
  79       native_prio = os::java_to_os_priority[CriticalPriority];
  80     } else {
  81       native_prio = os::java_to_os_priority[NearMaxPriority];
  82     }
  83     os::set_native_priority(this, native_prio);
  84 
  85     if (!DisableStartThread) {
  86       os::start_thread(this);
  87     }
  88   }
  89   _sltMonitor = SLT_lock;
  90 }
  91 
  92 void ConcurrentMarkSweepThread::run() {
  93   assert(this == cmst(), "just checking");
  94 
  95   initialize_in_thread();
  96   // From this time Thread::current() should be working.
  97   assert(this == Thread::current(), "just checking");
  98   if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
  99     warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
 100   }
 101   // Wait until Universe::is_fully_initialized()
 102   {
 103     CMSLoopCountWarn loopX("CMS::run", "waiting for "
 104                            "Universe::is_fully_initialized()", 2);
 105     MutexLockerEx x(CGC_lock, true);
 106     set_CMS_flag(CMS_cms_wants_token);
 107     // Wait until Universe is initialized and all initialization is completed.
 108     while (!is_init_completed() && !Universe::is_fully_initialized() &&
 109            !_should_terminate) {
 110       CGC_lock->wait(true, 200);
 111       loopX.tick();
 112     }
 113     // Wait until the surrogate locker thread that will do
 114     // pending list locking on our behalf has been created.
 115     // We cannot start the SLT thread ourselves since we need
 116     // to be a JavaThread to do so.
 117     CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
 118     while (_slt == NULL && !_should_terminate) {
 119       CGC_lock->wait(true, 200);
 120       loopY.tick();
 121     }
 122     clear_CMS_flag(CMS_cms_wants_token);
 123   }
 124 
 125   while (!_should_terminate) {
 126     sleepBeforeNextCycle();
 127     if (_should_terminate) break;
 128     GCIdMark gc_id_mark;
 129     GCCause::Cause cause = _collector->_full_gc_requested ?
 130       _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
 131     _collector->collect_in_background(cause);
 132   }
 133   assert(_should_terminate, "just checking");
 134   // Check that the state of any protocol for synchronization
 135   // between background (CMS) and foreground collector is "clean"
 136   // (i.e. will not potentially block the foreground collector,
 137   // requiring action by us).
 138   verify_ok_to_terminate();
 139   // Signal that it is terminated
 140   {
 141     MutexLockerEx mu(Terminator_lock,
 142                      Mutex::_no_safepoint_check_flag);
 143     assert(_cmst == this, "Weird!");
 144     _cmst = NULL;
 145     Terminator_lock->notify();
 146   }
 147 }
 148 
 149 #ifndef PRODUCT
 150 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
 151   assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
 152            cms_thread_wants_cms_token()),
 153          "Must renounce all worldly possessions and desires for nirvana");
 154   _collector->verify_ok_to_terminate();
 155 }
 156 #endif
 157 
 158 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
 159 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
 160   if (!_should_terminate) {
 161     assert(cmst() == NULL, "start() called twice?");
 162     ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
 163     assert(cmst() == th, "Where did the just-created CMS thread go?");
 164     return th;
 165   }
 166   return NULL;
 167 }
 168 
 169 void ConcurrentMarkSweepThread::stop() {
 170   // it is ok to take late safepoints here, if needed
 171   {
 172     MutexLockerEx x(Terminator_lock);
 173     _should_terminate = true;
 174   }
 175   { // Now post a notify on CGC_lock so as to nudge
 176     // CMS thread(s) that might be slumbering in
 177     // sleepBeforeNextCycle.
 178     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 179     CGC_lock->notify_all();
 180   }
 181   { // Now wait until (all) CMS thread(s) have exited
 182     MutexLockerEx x(Terminator_lock);
 183     while(cmst() != NULL) {
 184       Terminator_lock->wait();
 185     }
 186   }
 187 }
 188 
 189 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
 190   assert(tc != NULL, "Null ThreadClosure");
 191   if (_cmst != NULL) {
 192     tc->do_thread(_cmst);
 193   }
 194   assert(Universe::is_fully_initialized(),
 195          "Called too early, make sure heap is fully initialized");
 196   if (_collector != NULL) {
 197     AbstractWorkGang* gang = _collector->conc_workers();
 198     if (gang != NULL) {
 199       gang->threads_do(tc);
 200     }
 201   }
 202 }
 203 
 204 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
 205   if (_cmst != NULL) {
 206     _cmst->print_on(st);
 207     st->cr();
 208   }
 209   if (_collector != NULL) {
 210     AbstractWorkGang* gang = _collector->conc_workers();
 211     if (gang != NULL) {
 212       gang->print_worker_threads_on(st);
 213     }
 214   }
 215 }
 216 
 217 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
 218   assert(UseConcMarkSweepGC, "just checking");
 219 
 220   MutexLockerEx x(CGC_lock,
 221                   Mutex::_no_safepoint_check_flag);
 222   if (!is_cms_thread) {
 223     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 224     CMSSynchronousYieldRequest yr;
 225     while (CMS_flag_is_set(CMS_cms_has_token)) {
 226       // indicate that we want to get the token
 227       set_CMS_flag(CMS_vm_wants_token);
 228       CGC_lock->wait(true);
 229     }
 230     // claim the token and proceed
 231     clear_CMS_flag(CMS_vm_wants_token);
 232     set_CMS_flag(CMS_vm_has_token);
 233   } else {
 234     assert(Thread::current()->is_ConcurrentGC_thread(),
 235            "Not a CMS thread");
 236     // The following barrier assumes there's only one CMS thread.
 237     // This will need to be modified is there are more CMS threads than one.
 238     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
 239       set_CMS_flag(CMS_cms_wants_token);
 240       CGC_lock->wait(true);
 241     }
 242     // claim the token
 243     clear_CMS_flag(CMS_cms_wants_token);
 244     set_CMS_flag(CMS_cms_has_token);
 245   }
 246 }
 247 
 248 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
 249   assert(UseConcMarkSweepGC, "just checking");
 250 
 251   MutexLockerEx x(CGC_lock,
 252                   Mutex::_no_safepoint_check_flag);
 253   if (!is_cms_thread) {
 254     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 255     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
 256     clear_CMS_flag(CMS_vm_has_token);
 257     if (CMS_flag_is_set(CMS_cms_wants_token)) {
 258       // wake-up a waiting CMS thread
 259       CGC_lock->notify();
 260     }
 261     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
 262            "Should have been cleared");
 263   } else {
 264     assert(Thread::current()->is_ConcurrentGC_thread(),
 265            "Not a CMS thread");
 266     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
 267     clear_CMS_flag(CMS_cms_has_token);
 268     if (CMS_flag_is_set(CMS_vm_wants_token)) {
 269       // wake-up a waiting VM thread
 270       CGC_lock->notify();
 271     }
 272     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 273            "Should have been cleared");
 274   }
 275 }
 276 
 277 // Wait until any cms_lock event
 278 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
 279   MutexLockerEx x(CGC_lock,
 280                   Mutex::_no_safepoint_check_flag);
 281   if (_should_terminate || _collector->_full_gc_requested) {
 282     return;
 283   }
 284   set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 285   CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
 286   clear_CMS_flag(CMS_cms_wants_token);
 287   assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 288          "Should not be set");
 289 }
 290 
 291 // Wait until the next synchronous GC, a concurrent full gc request,
 292 // or a timeout, whichever is earlier.
 293 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
 294   // Wait time in millis or 0 value representing infinite wait for a scavenge
 295   assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
 296 
 297   GenCollectedHeap* gch = GenCollectedHeap::heap();
 298   double start_time_secs = os::elapsedTime();
 299   double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
 300 
 301   // Total collections count before waiting loop
 302   unsigned int before_count;
 303   {
 304     MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 305     before_count = gch->total_collections();
 306   }
 307 
 308   unsigned int loop_count = 0;
 309 
 310   while(!_should_terminate) {
 311     double now_time = os::elapsedTime();
 312     long wait_time_millis;
 313 
 314     if(t_millis != 0) {
 315       // New wait limit
 316       wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
 317       if(wait_time_millis <= 0) {
 318         // Wait time is over
 319         break;
 320       }
 321     } else {
 322       // No wait limit, wait if necessary forever
 323       wait_time_millis = 0;
 324     }
 325 
 326     // Wait until the next event or the remaining timeout
 327     {
 328       MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 329 
 330       if (_should_terminate || _collector->_full_gc_requested) {
 331         return;
 332       }
 333       set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 334       assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
 335       CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
 336       clear_CMS_flag(CMS_cms_wants_token);
 337       assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 338              "Should not be set");
 339     }
 340 
 341     // Extra wait time check before entering the heap lock to get the collection count
 342     if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
 343       // Wait time is over
 344       break;
 345     }
 346 
 347     // Total collections count after the event
 348     unsigned int after_count;
 349     {
 350       MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 351       after_count = gch->total_collections();
 352     }
 353 
 354     if(before_count != after_count) {
 355       // There was a collection - success
 356       break;
 357     }
 358 
 359     // Too many loops warning
 360     if(++loop_count == 0) {
 361       warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
 362     }
 363   }
 364 }
 365 
 366 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
 367   while (!_should_terminate) {
 368     if(CMSWaitDuration >= 0) {
 369       // Wait until the next synchronous GC, a concurrent full gc
 370       // request or a timeout, whichever is earlier.
 371       wait_on_cms_lock_for_scavenge(CMSWaitDuration);
 372     } else {
 373       // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
 374       wait_on_cms_lock(CMSCheckInterval);
 375     }
 376     // Check if we should start a CMS collection cycle
 377     if (_collector->shouldConcurrentCollect()) {
 378       return;
 379     }
 380     // .. collection criterion not yet met, let's go back
 381     // and wait some more
 382   }
 383 }
 384 
 385 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 386 // which is a non-JavaThread, can only be called by a JavaThread.
 387 // Currently this is done at vm creation time (post-vm-init) by the
 388 // main/Primordial (Java)Thread.
 389 // XXX Consider changing this in the future to allow the CMS thread
 390 // itself to create this thread?
 391 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
 392   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
 393   assert(_slt == NULL, "SLT already created");
 394   _slt = SurrogateLockerThread::make(THREAD);
 395 }