1 /*
   2  * Copyright (c) 2001, 2013, 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 "gc_implementation/g1/concurrentMarkThread.inline.hpp"
  27 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
  28 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
  29 #include "gc_implementation/g1/g1Log.hpp"
  30 #include "gc_implementation/g1/g1MMUTracker.hpp"
  31 #include "gc_implementation/g1/vm_operations_g1.hpp"
  32 #include "memory/resourceArea.hpp"
  33 #include "runtime/vmThread.hpp"
  34 
  35 // ======= Concurrent Mark Thread ========
  36 
  37 // The CM thread is created when the G1 garbage collector is used
  38 
  39 SurrogateLockerThread*
  40      ConcurrentMarkThread::_slt = NULL;
  41 
  42 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
  43   ConcurrentGCThread(),
  44   _cm(cm),
  45   _started(false),
  46   _in_progress(false),
  47   _vtime_accum(0.0),
  48   _vtime_mark_accum(0.0) {
  49   create_and_start();
  50 }
  51 
  52 class CMCheckpointRootsFinalClosure: public VoidClosure {
  53 
  54   ConcurrentMark* _cm;
  55 public:
  56 
  57   CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
  58     _cm(cm) {}
  59 
  60   void do_void(){
  61     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
  62   }
  63 };
  64 
  65 class CMCleanUp: public VoidClosure {
  66   ConcurrentMark* _cm;
  67 public:
  68 
  69   CMCleanUp(ConcurrentMark* cm) :
  70     _cm(cm) {}
  71 
  72   void do_void(){
  73     _cm->cleanup();
  74   }
  75 };
  76 
  77 
  78 
  79 void ConcurrentMarkThread::run() {
  80   initialize_in_thread();
  81   _vtime_start = os::elapsedVTime();
  82   wait_for_universe_init();
  83 
  84   G1CollectedHeap* g1h = G1CollectedHeap::heap();
  85   G1CollectorPolicy* g1_policy = g1h->g1_policy();
  86   G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
  87   Thread *current_thread = Thread::current();
  88 
  89   while (!_should_terminate) {
  90     // wait until started is set.
  91     sleepBeforeNextCycle();
  92     {
  93       ResourceMark rm;
  94       HandleMark   hm;
  95       double cycle_start = os::elapsedVTime();
  96       char verbose_str[128];
  97 
  98       // We have to ensure that we finish scanning the root regions
  99       // before the next GC takes place. To ensure this we have to
 100       // make sure that we do not join the STS until the root regions
 101       // have been scanned. If we did then it's possible that a
 102       // subsequent GC could block us from joining the STS and proceed
 103       // without the root regions have been scanned which would be a
 104       // correctness issue.
 105 
 106       double scan_start = os::elapsedTime();
 107       if (!cm()->has_aborted()) {
 108         if (G1Log::fine()) {
 109           gclog_or_tty->date_stamp(PrintGCDateStamps);
 110           gclog_or_tty->stamp(PrintGCTimeStamps);
 111           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
 112         }
 113 
 114         _cm->scanRootRegions();
 115 
 116         double scan_end = os::elapsedTime();
 117         if (G1Log::fine()) {
 118           gclog_or_tty->date_stamp(PrintGCDateStamps);
 119           gclog_or_tty->stamp(PrintGCTimeStamps);
 120           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf]",
 121                                  scan_end - scan_start);
 122         }
 123       }
 124 
 125       double mark_start_sec = os::elapsedTime();
 126       if (G1Log::fine()) {
 127         gclog_or_tty->date_stamp(PrintGCDateStamps);
 128         gclog_or_tty->stamp(PrintGCTimeStamps);
 129         gclog_or_tty->print_cr("[GC concurrent-mark-start]");
 130       }
 131 
 132       int iter = 0;
 133       do {
 134         iter++;
 135         if (!cm()->has_aborted()) {
 136           _cm->markFromRoots();
 137         }
 138 
 139         double mark_end_time = os::elapsedVTime();
 140         double mark_end_sec = os::elapsedTime();
 141         _vtime_mark_accum += (mark_end_time - cycle_start);
 142         if (!cm()->has_aborted()) {
 143           if (g1_policy->adaptive_young_list_length()) {
 144             double now = os::elapsedTime();
 145             double remark_prediction_ms = g1_policy->predict_remark_time_ms();
 146             jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
 147             os::sleep(current_thread, sleep_time_ms, false);
 148           }
 149 
 150           if (G1Log::fine()) {
 151             gclog_or_tty->date_stamp(PrintGCDateStamps);
 152             gclog_or_tty->stamp(PrintGCTimeStamps);
 153             gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf sec]",
 154                                       mark_end_sec - mark_start_sec);
 155           }
 156 
 157           CMCheckpointRootsFinalClosure final_cl(_cm);
 158           sprintf(verbose_str, "GC remark");
 159           VM_CGC_Operation op(&final_cl, verbose_str, true /* needs_pll */);
 160           VMThread::execute(&op);
 161         }
 162         if (cm()->restart_for_overflow()) {
 163           if (G1TraceMarkStackOverflow) {
 164             gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
 165                                    "in remark (restart #%d).", iter);
 166           }
 167           if (G1Log::fine()) {
 168             gclog_or_tty->date_stamp(PrintGCDateStamps);
 169             gclog_or_tty->stamp(PrintGCTimeStamps);
 170             gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
 171           }
 172         }
 173       } while (cm()->restart_for_overflow());
 174 
 175       double end_time = os::elapsedVTime();
 176       // Update the total virtual time before doing this, since it will try
 177       // to measure it to get the vtime for this marking.  We purposely
 178       // neglect the presumably-short "completeCleanup" phase here.
 179       _vtime_accum = (end_time - _vtime_start);
 180 
 181       if (!cm()->has_aborted()) {
 182         if (g1_policy->adaptive_young_list_length()) {
 183           double now = os::elapsedTime();
 184           double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
 185           jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
 186           os::sleep(current_thread, sleep_time_ms, false);
 187         }
 188 
 189         CMCleanUp cl_cl(_cm);
 190         sprintf(verbose_str, "GC cleanup");
 191         VM_CGC_Operation op(&cl_cl, verbose_str, false /* needs_pll */);
 192         VMThread::execute(&op);
 193       } else {
 194         // We don't want to update the marking status if a GC pause
 195         // is already underway.
 196         _sts.join();
 197         g1h->set_marking_complete();
 198         _sts.leave();
 199       }
 200 
 201       // Check if cleanup set the free_regions_coming flag. If it
 202       // hasn't, we can just skip the next step.
 203       if (g1h->free_regions_coming()) {
 204         // The following will finish freeing up any regions that we
 205         // found to be empty during cleanup. We'll do this part
 206         // without joining the suspendible set. If an evacuation pause
 207         // takes place, then we would carry on freeing regions in
 208         // case they are needed by the pause. If a Full GC takes
 209         // place, it would wait for us to process the regions
 210         // reclaimed by cleanup.
 211 
 212         double cleanup_start_sec = os::elapsedTime();
 213         if (G1Log::fine()) {
 214           gclog_or_tty->date_stamp(PrintGCDateStamps);
 215           gclog_or_tty->stamp(PrintGCTimeStamps);
 216           gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
 217         }
 218 
 219         // Now do the concurrent cleanup operation.
 220         _cm->completeCleanup();
 221 
 222         // Notify anyone who's waiting that there are no more free
 223         // regions coming. We have to do this before we join the STS
 224         // (in fact, we should not attempt to join the STS in the
 225         // interval between finishing the cleanup pause and clearing
 226         // the free_regions_coming flag) otherwise we might deadlock:
 227         // a GC worker could be blocked waiting for the notification
 228         // whereas this thread will be blocked for the pause to finish
 229         // while it's trying to join the STS, which is conditional on
 230         // the GC workers finishing.
 231         g1h->reset_free_regions_coming();
 232 
 233         double cleanup_end_sec = os::elapsedTime();
 234         if (G1Log::fine()) {
 235           gclog_or_tty->date_stamp(PrintGCDateStamps);
 236           gclog_or_tty->stamp(PrintGCTimeStamps);
 237           gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf]",
 238                                  cleanup_end_sec - cleanup_start_sec);
 239         }
 240       }
 241       guarantee(cm()->cleanup_list_is_empty(),
 242                 "at this point there should be no regions on the cleanup list");
 243 
 244       // There is a tricky race before recording that the concurrent
 245       // cleanup has completed and a potential Full GC starting around
 246       // the same time. We want to make sure that the Full GC calls
 247       // abort() on concurrent mark after
 248       // record_concurrent_mark_cleanup_completed(), since abort() is
 249       // the method that will reset the concurrent mark state. If we
 250       // end up calling record_concurrent_mark_cleanup_completed()
 251       // after abort() then we might incorrectly undo some of the work
 252       // abort() did. Checking the has_aborted() flag after joining
 253       // the STS allows the correct ordering of the two methods. There
 254       // are two scenarios:
 255       //
 256       // a) If we reach here before the Full GC, the fact that we have
 257       // joined the STS means that the Full GC cannot start until we
 258       // leave the STS, so record_concurrent_mark_cleanup_completed()
 259       // will complete before abort() is called.
 260       //
 261       // b) If we reach here during the Full GC, we'll be held up from
 262       // joining the STS until the Full GC is done, which means that
 263       // abort() will have completed and has_aborted() will return
 264       // true to prevent us from calling
 265       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 266       // not needed any more as the concurrent mark state has been
 267       // already reset).
 268       _sts.join();
 269       if (!cm()->has_aborted()) {
 270         g1_policy->record_concurrent_mark_cleanup_completed();
 271       }
 272       _sts.leave();
 273 
 274       if (cm()->has_aborted()) {
 275         if (G1Log::fine()) {
 276           gclog_or_tty->date_stamp(PrintGCDateStamps);
 277           gclog_or_tty->stamp(PrintGCTimeStamps);
 278           gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
 279         }
 280       }
 281 
 282       // We now want to allow clearing of the marking bitmap to be
 283       // suspended by a collection pause.
 284       _sts.join();
 285       _cm->clearNextBitmap();
 286       _sts.leave();
 287     }
 288 
 289     // Update the number of full collections that have been
 290     // completed. This will also notify the FullGCCount_lock in case a
 291     // Java thread is waiting for a full GC to happen (e.g., it
 292     // called System.gc() with +ExplicitGCInvokesConcurrent).
 293     _sts.join();
 294     g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 295     _sts.leave();
 296   }
 297   assert(_should_terminate, "just checking");
 298 
 299   terminate();
 300 }
 301 
 302 
 303 void ConcurrentMarkThread::yield() {
 304   _sts.yield("Concurrent Mark");
 305 }
 306 
 307 void ConcurrentMarkThread::stop() {
 308   // it is ok to take late safepoints here, if needed
 309   MutexLockerEx mu(Terminator_lock);
 310   _should_terminate = true;
 311   while (!_has_terminated) {
 312     Terminator_lock->wait();
 313   }
 314 }
 315 
 316 void ConcurrentMarkThread::print() const {
 317   print_on(tty);
 318 }
 319 
 320 void ConcurrentMarkThread::print_on(outputStream* st) const {
 321   st->print("\"G1 Main Concurrent Mark GC Thread\" ");
 322   Thread::print_on(st);
 323   st->cr();
 324 }
 325 
 326 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 327   // We join here because we don't want to do the "shouldConcurrentMark()"
 328   // below while the world is otherwise stopped.
 329   assert(!in_progress(), "should have been cleared");
 330 
 331   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 332   while (!started()) {
 333     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 334   }
 335   set_in_progress();
 336   clear_started();
 337 }
 338 
 339 // Note: As is the case with CMS - this method, although exported
 340 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
 341 // be called by a JavaThread. Currently this is done at vm creation
 342 // time (post-vm-init) by the main/Primordial (Java)Thread.
 343 // XXX Consider changing this in the future to allow the CM thread
 344 // itself to create this thread?
 345 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
 346   assert(UseG1GC, "SLT thread needed only for concurrent GC");
 347   assert(THREAD->is_Java_thread(), "must be a Java thread");
 348   assert(_slt == NULL, "SLT already created");
 349   _slt = SurrogateLockerThread::make(THREAD);
 350 }