/*

 * Copyright (c) 2015, 2017, 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 "gc/g1/g1CollectedHeap.inline.hpp"

#include "gc/g1/g1CollectionSet.hpp"

#include "gc/g1/g1ConcurrentMark.inline.hpp"

#include "gc/g1/g1ConcurrentMarkThread.inline.hpp"

#include "gc/g1/g1Policy.hpp"

#include "gc/g1/g1YoungRemSetSamplingThread.hpp"

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

#include "gc/g1/heapRegionRemSet.hpp"

#include "gc/shared/suspendibleThreadSet.hpp"

#include "runtime/mutexLocker.hpp"

G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :

    ConcurrentGCThread(),

    _monitor(Mutex::nonleaf,

             "G1YoungRemSetSamplingThread monitor",

             true,

             Monitor::_safepoint_check_never),

    _last_periodic_gc_attempt_s(os::elapsedTime()) {

  set_name("G1 Young RemSet Sampling");

  create_and_start();

}

void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {

  MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);

  if (!should_terminate()) {

    uintx waitms = G1ConcRefinementServiceIntervalMillis;

    _monitor.wait(Mutex::_no_safepoint_check_flag, waitms);

  }

}

bool G1YoungRemSetSamplingThread::should_start_periodic_gc() {

  // If we are currently in a concurrent mark we are going to uncommit memory soon.

  if (G1CollectedHeap::heap()->concurrent_mark()->cm_thread()->during_cycle()) {

    log_debug(gc, periodic)("Concurrent cycle in progress. Skipping.");

    return false;

  }

  // Check if enough time has passed since the last GC.

    log_debug(gc, periodic)("Last GC occurred " UINTX_FORMAT "ms before which is below threshold " UINTX_FORMAT "ms. Skipping.",

                            time_since_last_gc, G1PeriodicGCInterval);

    return false;

  }

  // Check if load is lower than max.

  double recent_load;

  if ((G1PeriodicGCSystemLoadThreshold > 0.0f) &&

      (os::loadavg(&recent_load, 1) == -1 || recent_load > G1PeriodicGCSystemLoadThreshold)) {

    log_debug(gc, periodic)("Load %1.2f is higher than threshold %1.2f. Skipping.",

                            recent_load, G1PeriodicGCSystemLoadThreshold);

    return false;

  }

  return true;

}

void G1YoungRemSetSamplingThread::check_for_periodic_gc(){

  if ((os::elapsedTime() - _last_periodic_gc_attempt_s) > (G1PeriodicGCInterval / 1000.0)) {

    log_debug(gc, periodic)("Checking for periodic GC.");

    if (should_start_periodic_gc()) {

      Universe::heap()->collect(GCCause::_g1_periodic_collection);

    }

    _last_periodic_gc_attempt_s = os::elapsedTime();

  }

}

void G1YoungRemSetSamplingThread::run_service() {

  double vtime_start = os::elapsedVTime();

  while (!should_terminate()) {

    sample_young_list_rs_lengths();

    if (os::supports_vtime()) {

      _vtime_accum = (os::elapsedVTime() - vtime_start);

    } else {

      _vtime_accum = 0.0;

    }

    check_for_periodic_gc();

    sleep_before_next_cycle();

  }

}

void G1YoungRemSetSamplingThread::stop_service() {

  MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);

  _monitor.notify();

}

class G1YoungRemSetSamplingClosure : public HeapRegionClosure {

  SuspendibleThreadSetJoiner* _sts;

  size_t _regions_visited;

  size_t _sampled_rs_lengths;

public:

  G1YoungRemSetSamplingClosure(SuspendibleThreadSetJoiner* sts) :

    HeapRegionClosure(), _sts(sts), _regions_visited(0), _sampled_rs_lengths(0) { }

  virtual bool do_heap_region(HeapRegion* r) {

    size_t rs_length = r->rem_set()->occupied();

    _sampled_rs_lengths += rs_length;

    // Update the collection set policy information for this region

    G1CollectedHeap::heap()->collection_set()->update_young_region_prediction(r, rs_length);

    _regions_visited++;

    if (_regions_visited == 10) {

      if (_sts->should_yield()) {

        _sts->yield();

        // A gc may have occurred and our sampling data is stale and further

        // traversal of the collection set is unsafe

        return true;

      }

      _regions_visited = 0;

    }

    return false;

  }

  size_t sampled_rs_lengths() const { return _sampled_rs_lengths; }

};

void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {

  SuspendibleThreadSetJoiner sts;

  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  G1Policy* g1p = g1h->g1_policy();

  if (g1p->adaptive_young_list_length()) {

    G1YoungRemSetSamplingClosure cl(&sts);

    G1CollectionSet* g1cs = g1h->collection_set();

    g1cs->iterate(&cl);

    if (cl.is_complete()) {

      g1p->revise_young_list_target_length_if_necessary(cl.sampled_rs_lengths());

    }

  }

}