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 "gc_implementation/shared/gcTrace.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "runtime/vmThread.hpp"
  35 
  36 // ======= Concurrent Mark Thread ========
  37 
  38 // The CM thread is created when the G1 garbage collector is used
  39 
  40 SurrogateLockerThread*
  41      ConcurrentMarkThread::_slt = NULL;
  42 
  43 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
  44   ConcurrentGCThread(),
  45   _cm(cm),
  46   _started(false),
  47   _in_progress(false),
  48   _vtime_accum(0.0),
  49   _vtime_mark_accum(0.0) {
  50 
  51   set_name("G1 Main Concurrent Mark GC Thread");
  52   create_and_start();
  53 }
  54 
  55 class CMCheckpointRootsFinalClosure: public VoidClosure {
  56 
  57   ConcurrentMark* _cm;
  58 public:
  59 
  60   CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
  61     _cm(cm) {}
  62 
  63   void do_void(){
  64     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
  65   }
  66 };
  67 
  68 class CMCleanUp: public VoidClosure {
  69   ConcurrentMark* _cm;
  70 public:
  71 
  72   CMCleanUp(ConcurrentMark* cm) :
  73     _cm(cm) {}
  74 
  75   void do_void(){
  76     _cm->cleanup();
  77   }
  78 };
  79 
  80 
  81 
  82 void ConcurrentMarkThread::run() {
  83   initialize_in_thread();
  84   _vtime_start = os::elapsedVTime();
  85   wait_for_universe_init();
  86 
  87   G1CollectedHeap* g1h = G1CollectedHeap::heap();
  88   G1CollectorPolicy* g1_policy = g1h->g1_policy();
  89   G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
  90   Thread *current_thread = Thread::current();
  91 
  92   while (!_should_terminate) {
  93     // wait until started is set.
  94     sleepBeforeNextCycle();
  95     if (_should_terminate) {
  96       break;
  97     }
  98 
  99     {
 100       ResourceMark rm;
 101       HandleMark   hm;
 102       double cycle_start = os::elapsedVTime();
 103 
 104       // We have to ensure that we finish scanning the root regions
 105       // before the next GC takes place. To ensure this we have to
 106       // make sure that we do not join the STS until the root regions
 107       // have been scanned. If we did then it's possible that a
 108       // subsequent GC could block us from joining the STS and proceed
 109       // without the root regions have been scanned which would be a
 110       // correctness issue.
 111 
 112       double scan_start = os::elapsedTime();
 113       if (!cm()->has_aborted()) {
 114         if (G1Log::fine()) {
 115           gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 116           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
 117         }
 118 
 119         _cm->scanRootRegions();
 120 
 121         double scan_end = os::elapsedTime();
 122         if (G1Log::fine()) {
 123           gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 124           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
 125                                  scan_end - scan_start);
 126         }
 127       }
 128 
 129       double mark_start_sec = os::elapsedTime();
 130       if (G1Log::fine()) {
 131         gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 132         gclog_or_tty->print_cr("[GC concurrent-mark-start]");
 133       }
 134 
 135       int iter = 0;
 136       do {
 137         iter++;
 138         if (!cm()->has_aborted()) {
 139           _cm->markFromRoots();
 140         }
 141 
 142         double mark_end_time = os::elapsedVTime();
 143         double mark_end_sec = os::elapsedTime();
 144         _vtime_mark_accum += (mark_end_time - cycle_start);
 145         if (!cm()->has_aborted()) {
 146           if (g1_policy->adaptive_young_list_length()) {
 147             double now = os::elapsedTime();
 148             double remark_prediction_ms = g1_policy->predict_remark_time_ms();
 149             jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
 150             os::sleep(current_thread, sleep_time_ms, false);
 151           }
 152 
 153           if (G1Log::fine()) {
 154             gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 155             gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
 156                                       mark_end_sec - mark_start_sec);
 157           }
 158 
 159           CMCheckpointRootsFinalClosure final_cl(_cm);
 160           VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
 161           VMThread::execute(&op);
 162         }
 163         if (cm()->restart_for_overflow()) {
 164           if (G1TraceMarkStackOverflow) {
 165             gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
 166                                    "in remark (restart #%d).", iter);
 167           }
 168           if (G1Log::fine()) {
 169             gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 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         VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
 191         VMThread::execute(&op);
 192       } else {
 193         // We don't want to update the marking status if a GC pause
 194         // is already underway.
 195         SuspendibleThreadSetJoiner sts;
 196         g1h->set_marking_complete();
 197       }
 198 
 199       // Check if cleanup set the free_regions_coming flag. If it
 200       // hasn't, we can just skip the next step.
 201       if (g1h->free_regions_coming()) {
 202         // The following will finish freeing up any regions that we
 203         // found to be empty during cleanup. We'll do this part
 204         // without joining the suspendible set. If an evacuation pause
 205         // takes place, then we would carry on freeing regions in
 206         // case they are needed by the pause. If a Full GC takes
 207         // place, it would wait for us to process the regions
 208         // reclaimed by cleanup.
 209 
 210         double cleanup_start_sec = os::elapsedTime();
 211         if (G1Log::fine()) {
 212           gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 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->gclog_stamp(cm()->concurrent_gc_id());
 233           gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
 234                                  cleanup_end_sec - cleanup_start_sec);
 235         }
 236       }
 237       guarantee(cm()->cleanup_list_is_empty(),
 238                 "at this point there should be no regions on the cleanup list");
 239 
 240       // There is a tricky race before recording that the concurrent
 241       // cleanup has completed and a potential Full GC starting around
 242       // the same time. We want to make sure that the Full GC calls
 243       // abort() on concurrent mark after
 244       // record_concurrent_mark_cleanup_completed(), since abort() is
 245       // the method that will reset the concurrent mark state. If we
 246       // end up calling record_concurrent_mark_cleanup_completed()
 247       // after abort() then we might incorrectly undo some of the work
 248       // abort() did. Checking the has_aborted() flag after joining
 249       // the STS allows the correct ordering of the two methods. There
 250       // are two scenarios:
 251       //
 252       // a) If we reach here before the Full GC, the fact that we have
 253       // joined the STS means that the Full GC cannot start until we
 254       // leave the STS, so record_concurrent_mark_cleanup_completed()
 255       // will complete before abort() is called.
 256       //
 257       // b) If we reach here during the Full GC, we'll be held up from
 258       // joining the STS until the Full GC is done, which means that
 259       // abort() will have completed and has_aborted() will return
 260       // true to prevent us from calling
 261       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 262       // not needed any more as the concurrent mark state has been
 263       // already reset).
 264       {
 265         SuspendibleThreadSetJoiner sts;
 266         if (!cm()->has_aborted()) {
 267           g1_policy->record_concurrent_mark_cleanup_completed();
 268         }
 269       }
 270 
 271       if (cm()->has_aborted()) {
 272         if (G1Log::fine()) {
 273           gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
 274           gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
 275         }
 276       }
 277 
 278       // We now want to allow clearing of the marking bitmap to be
 279       // suspended by a collection pause.
 280       // We may have aborted just before the remark. Do not bother clearing the
 281       // bitmap then, as it has been done during mark abort.
 282       if (!cm()->has_aborted()) {
 283         _cm->clearNextBitmap();
 284       } else {
 285         assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
 286       }
 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     {
 294       SuspendibleThreadSetJoiner sts;
 295       g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 296       g1h->register_concurrent_cycle_end();
 297     }
 298   }
 299   assert(_should_terminate, "just checking");
 300 
 301   terminate();
 302 }
 303 
 304 void ConcurrentMarkThread::stop() {
 305   {
 306     MutexLockerEx ml(Terminator_lock);
 307     _should_terminate = true;
 308   }
 309 
 310   {
 311     MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
 312     CGC_lock->notify_all();
 313   }
 314 
 315   {
 316     MutexLockerEx ml(Terminator_lock);
 317     while (!_has_terminated) {
 318       Terminator_lock->wait();
 319     }
 320   }
 321 }
 322 
 323 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 324   // We join here because we don't want to do the "shouldConcurrentMark()"
 325   // below while the world is otherwise stopped.
 326   assert(!in_progress(), "should have been cleared");
 327 
 328   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 329   while (!started() && !_should_terminate) {
 330     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 331   }
 332 
 333   if (started()) {
 334     set_in_progress();
 335     clear_started();
 336   }
 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 }