/*

 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#include "precompiled.hpp"

#include "classfile/classLoaderData.hpp"

#include "gc/g1/concurrentMarkThread.inline.hpp"

#include "gc/g1/g1CollectedHeap.inline.hpp"

#include "gc/g1/g1CollectorPolicy.hpp"

#include "gc/g1/g1MMUTracker.hpp"

#include "gc/g1/suspendibleThreadSet.hpp"

#include "gc/g1/vm_operations_g1.hpp"

#include "gc/shared/gcId.hpp"

#include "gc/shared/gcTrace.hpp"

#include "gc/shared/gcTraceTime.inline.hpp"

#include "logging/log.hpp"

#include "memory/resourceArea.hpp"

#include "runtime/vmThread.hpp"

// ======= Concurrent Mark Thread ========

// The CM thread is created when the G1 garbage collector is used

ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :

  ConcurrentGCThread(),

  _cm(cm),

  _state(Idle),

  _vtime_accum(0.0),

  _vtime_mark_accum(0.0) {

  set_name("G1 Main Marker");

  create_and_start();

}

class CMCheckpointRootsFinalClosure: public VoidClosure {

  G1ConcurrentMark* _cm;

public:

  CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :

    _cm(cm) {}

  void do_void(){

    _cm->checkpointRootsFinal(false); // !clear_all_soft_refs

  }

};

class CMCleanUp: public VoidClosure {

  G1ConcurrentMark* _cm;

public:

  CMCleanUp(G1ConcurrentMark* cm) :

    _cm(cm) {}

  void do_void(){

    _cm->cleanup();

  }

};

// Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.

void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {

  if (g1_policy->adaptive_young_list_length()) {

    double now = os::elapsedTime();

    double prediction_ms = remark ? g1_policy->predict_remark_time_ms()

                                  : g1_policy->predict_cleanup_time_ms();

    G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();

    jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);

    os::sleep(this, sleep_time_ms, false);

  }

}

class G1ConcPhaseTimer : public GCTraceConcTimeImpl<LogLevel::Info, LOG_TAGS(gc, marking)> {

  G1ConcurrentMark* _cm;

 public:

  G1ConcPhaseTimer(G1ConcurrentMark* cm, const char* title) :

     GCTraceConcTimeImpl<LogLevel::Info,  LogTag::_gc, LogTag::_marking>(title),

     _cm(cm) {

    _cm->register_concurrent_phase_start(title);

  }

  ~G1ConcPhaseTimer() {

    _cm->register_concurrent_phase_end();

  }

};

void ConcurrentMarkThread::run_service() {

  _vtime_start = os::elapsedVTime();

  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  G1CollectorPolicy* g1_policy = g1h->g1_policy();

  while (!should_terminate()) {

    // wait until started is set.

    sleepBeforeNextCycle();

    if (should_terminate()) {

      break;

    }

    assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");

    GCTraceConcTime(Info, gc) tt("Concurrent Cycle");

    {

      ResourceMark rm;

      HandleMark   hm;

      double cycle_start = os::elapsedVTime();

      {

        G1ConcPhaseTimer t(_cm, "Concurrent Clear Claimed Marks");

        ClassLoaderDataGraph::clear_claimed_marks();

      }

      // We have to ensure that we finish scanning the root regions

      // before the next GC takes place. To ensure this we have to

      // make sure that we do not join the STS until the root regions

      // have been scanned. If we did then it's possible that a

      // subsequent GC could block us from joining the STS and proceed

      // without the root regions have been scanned which would be a

      // correctness issue.

      {

        G1ConcPhaseTimer t(_cm, "Concurrent Scan Root Regions");

        _cm->scan_root_regions();

      }

      // It would be nice to use the GCTraceConcTime class here but

      // the "end" logging is inside the loop and not at the end of

      // a scope. Mimicking the same log output as GCTraceConcTime instead.

      jlong mark_start = os::elapsed_counter();

      log_info(gc, marking)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));

      int iter = 0;

      do {

        iter++;

        if (!cm()->has_aborted()) {

          G1ConcPhaseTimer t(_cm, "Concurrent Mark From Roots");

          _cm->mark_from_roots();

        }

        double mark_end_time = os::elapsedVTime();

        jlong mark_end = os::elapsed_counter();

        _vtime_mark_accum += (mark_end_time - cycle_start);

        if (!cm()->has_aborted()) {

          delay_to_keep_mmu(g1_policy, true /* remark */);

          log_info(gc, marking)("Concurrent Mark (%.3fs, %.3fs) %.3fms",

                                TimeHelper::counter_to_seconds(mark_start),

                                TimeHelper::counter_to_seconds(mark_end),

                                TimeHelper::counter_to_millis(mark_end - mark_start));

          CMCheckpointRootsFinalClosure final_cl(_cm);

          VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);

          VMThread::execute(&op);

        }

        if (cm()->restart_for_overflow()) {

          log_debug(gc, marking)("Restarting Concurrent Marking because of Mark Stack Overflow in Remark (Iteration #%d).", iter);

          log_info(gc, marking)("Concurrent Mark Restart due to overflow");

        }

      } while (cm()->restart_for_overflow());

      double end_time = os::elapsedVTime();

      // Update the total virtual time before doing this, since it will try

      // to measure it to get the vtime for this marking.  We purposely

      // neglect the presumably-short "completeCleanup" phase here.

      _vtime_accum = (end_time - _vtime_start);

      if (!cm()->has_aborted()) {

        delay_to_keep_mmu(g1_policy, false /* cleanup */);

        CMCleanUp cl_cl(_cm);

        VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);

        VMThread::execute(&op);

      } else {

        // We don't want to update the marking status if a GC pause

        // is already underway.

        SuspendibleThreadSetJoiner sts_join;

        g1h->collector_state()->set_mark_in_progress(false);

      }

      // Check if cleanup set the free_regions_coming flag. If it

      // hasn't, we can just skip the next step.

      if (g1h->free_regions_coming()) {

        // The following will finish freeing up any regions that we

        // found to be empty during cleanup. We'll do this part

        // without joining the suspendible set. If an evacuation pause

        // takes place, then we would carry on freeing regions in

        // case they are needed by the pause. If a Full GC takes

        // place, it would wait for us to process the regions

        // reclaimed by cleanup.

        G1ConcPhaseTimer t(_cm, "Concurrent Complete Cleanup");

        // Now do the concurrent cleanup operation.

        _cm->complete_cleanup();

        // Notify anyone who's waiting that there are no more free

        // regions coming. We have to do this before we join the STS

        // (in fact, we should not attempt to join the STS in the

        // interval between finishing the cleanup pause and clearing

        // the free_regions_coming flag) otherwise we might deadlock:

        // a GC worker could be blocked waiting for the notification

        // whereas this thread will be blocked for the pause to finish

        // while it's trying to join the STS, which is conditional on

        // the GC workers finishing.

        g1h->reset_free_regions_coming();

      }

      guarantee(cm()->cleanup_list_is_empty(),

                "at this point there should be no regions on the cleanup list");

      // There is a tricky race before recording that the concurrent

      // cleanup has completed and a potential Full GC starting around

      // the same time. We want to make sure that the Full GC calls

      // abort() on concurrent mark after

      // record_concurrent_mark_cleanup_completed(), since abort() is

      // the method that will reset the concurrent mark state. If we

      // end up calling record_concurrent_mark_cleanup_completed()

      // after abort() then we might incorrectly undo some of the work

      // abort() did. Checking the has_aborted() flag after joining

      // the STS allows the correct ordering of the two methods. There

      // are two scenarios:

      //

      // a) If we reach here before the Full GC, the fact that we have

      // joined the STS means that the Full GC cannot start until we

      // leave the STS, so record_concurrent_mark_cleanup_completed()

      // will complete before abort() is called.

      //

      // b) If we reach here during the Full GC, we'll be held up from

      // joining the STS until the Full GC is done, which means that

      // abort() will have completed and has_aborted() will return

      // true to prevent us from calling

      // record_concurrent_mark_cleanup_completed() (and, in fact, it's

      // not needed any more as the concurrent mark state has been

      // already reset).

      {

        SuspendibleThreadSetJoiner sts_join;

        if (!cm()->has_aborted()) {

          g1_policy->record_concurrent_mark_cleanup_completed();

        } else {

          log_info(gc, marking)("Concurrent Mark Abort");

        }

      }

      // We now want to allow clearing of the marking bitmap to be

      // suspended by a collection pause.

      // We may have aborted just before the remark. Do not bother clearing the

      // bitmap then, as it has been done during mark abort.

      if (!cm()->has_aborted()) {

        G1ConcPhaseTimer t(_cm, "Concurrent Cleanup for Next Mark");

        _cm->cleanup_for_next_mark();

      } else {

        assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");

      }

    }

    // Update the number of full collections that have been

    // completed. This will also notify the FullGCCount_lock in case a

    // Java thread is waiting for a full GC to happen (e.g., it

    // called System.gc() with +ExplicitGCInvokesConcurrent).

    {

      SuspendibleThreadSetJoiner sts_join;

      g1h->increment_old_marking_cycles_completed(true /* concurrent */);

      g1h->register_concurrent_cycle_end();

    }

  }

  _cm->root_regions()->cancel_scan();

}

void ConcurrentMarkThread::stop_service() {

  MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);

  CGC_lock->notify_all();

}

void ConcurrentMarkThread::sleepBeforeNextCycle() {

  // We join here because we don't want to do the "shouldConcurrentMark()"

  // below while the world is otherwise stopped.

  assert(!in_progress(), "should have been cleared");

  MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);

  while (!started() && !should_terminate()) {

    CGC_lock->wait(Mutex::_no_safepoint_check_flag);

  }

  if (started()) {

    set_in_progress();

  }

}