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