/*

 * Copyright (c) 2015, 2019, 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/z/zCollectedHeap.hpp"

#include "gc/z/zDirector.hpp"

#include "gc/z/zHeap.inline.hpp"

#include "gc/z/zStat.hpp"

#include "gc/z/zUtils.hpp"

#include "logging/log.hpp"

const double ZDirector::one_in_1000 = 3.290527;

ZDirector::ZDirector() :

    _metronome(ZStatAllocRate::sample_hz) {

  set_name("ZDirector");

  create_and_start();

}

void ZDirector::sample_allocation_rate() const {

  // Sample allocation rate. This is needed by rule_allocation_rate()

  // below to estimate the time we have until we run out of memory.

  const double bytes_per_second = ZStatAllocRate::sample_and_reset();

  log_debug(gc, alloc)("Allocation Rate: %.3fMB/s, Avg: %.3f(+/-%.3f)MB/s",

                       bytes_per_second / M,

                       ZStatAllocRate::avg() / M,

                       ZStatAllocRate::avg_sd() / M);

}

bool ZDirector::rule_timer() const {

  if (ZCollectionInterval == 0) {

    // Rule disabled

    return false;

  }

  // Perform GC if timer has expired.

  const double time_since_last_gc = ZStatCycle::time_since_last();

  const double time_until_gc = ZCollectionInterval - time_since_last_gc;

  log_debug(gc, director)("Rule: Timer, Interval: %us, TimeUntilGC: %.3fs",

                          ZCollectionInterval, time_until_gc);

  return time_until_gc <= 0;

}

bool ZDirector::rule_warmup() const {

  if (ZStatCycle::is_warm()) {

    // Rule disabled

    return false;

  }

  // Perform GC if heap usage passes 10/20/30% and no other GC has been

  // performed yet. This allows us to get some early samples of the GC

  // duration, which is needed by the other rules.

  const size_t max_capacity = ZHeap::heap()->soft_max_capacity();

  const size_t used = ZHeap::heap()->used();

  const double used_threshold_percent = (ZStatCycle::ncycles() + 1) * 0.1;

  const size_t used_threshold = max_capacity * used_threshold_percent;

  log_debug(gc, director)("Rule: Warmup %.0f%%, Used: " SIZE_FORMAT "MB, UsedThreshold: " SIZE_FORMAT "MB",

                          used_threshold_percent * 100, used / M, used_threshold / M);

  return used >= used_threshold;

}

bool ZDirector::rule_allocation_rate() const {

  if (ZStatCycle::is_first()) {

    // Rule disabled

    return false;

  }

  // Perform GC if the estimated max allocation rate indicates that we

  // will run out of memory. The estimated max allocation rate is based

  // on the moving average of the sampled allocation rate plus a safety

  // margin based on variations in the allocation rate and unforeseen

  // allocation spikes.

  // Calculate amount of free memory available to Java threads. Note that

  // the heap reserve is not available to Java threads and is therefore not

  // considered part of the free memory.

  const size_t max_capacity = ZHeap::heap()->soft_max_capacity();

  const size_t max_reserve = ZHeap::heap()->max_reserve();

  const size_t used = ZHeap::heap()->used();

  const size_t free_with_reserve = max_capacity - MIN2(max_capacity, used);

  const size_t free = free_with_reserve - MIN2(free_with_reserve, max_reserve);

  // Calculate time until OOM given the max allocation rate and the amount

  // of free memory. The allocation rate is a moving average and we multiply

  // that with an allocation spike tolerance factor to guard against unforeseen

  // phase changes in the allocate rate. We then add ~3.3 sigma to account for

  // the allocation rate variance, which means the probability is 1 in 1000

  // that a sample is outside of the confidence interval.

  const double max_alloc_rate = (ZStatAllocRate::avg() * ZAllocationSpikeTolerance) + (ZStatAllocRate::avg_sd() * one_in_1000);

  const double time_until_oom = free / (max_alloc_rate + 1.0); // Plus 1.0B/s to avoid division by zero

  // Calculate max duration of a GC cycle. The duration of GC is a moving

  // average, we add ~3.3 sigma to account for the GC duration variance.

  const AbsSeq& duration_of_gc = ZStatCycle::normalized_duration();

  const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);

  // Calculate time until GC given the time until OOM and max duration of GC.

  // We also deduct the sample interval, so that we don't overshoot the target

  // time and end up starting the GC too late in the next interval.

  const double sample_interval = 1.0 / ZStatAllocRate::sample_hz;

  const double time_until_gc = time_until_oom - max_duration_of_gc - sample_interval;

  log_debug(gc, director)("Rule: Allocation Rate, MaxAllocRate: %.3fMB/s, Free: " SIZE_FORMAT "MB, MaxDurationOfGC: %.3fs, TimeUntilGC: %.3fs",

                          max_alloc_rate / M, free / M, max_duration_of_gc, time_until_gc);

  return time_until_gc <= 0;

}

bool ZDirector::rule_proactive() const {

  if (!ZProactive || !ZStatCycle::is_warm()) {

    // Rule disabled

    return false;

  }

  // Perform GC if the impact of doing so, in terms of application throughput

  // reduction, is considered acceptable. This rule allows us to keep the heap

  // size down and allow reference processing to happen even when we have a lot

  // of free space on the heap.

  // Only consider doing a proactive GC if the heap usage has grown by at least

  // 10% of the max capacity since the previous GC, or more than 5 minutes has

  // passed since the previous GC. This helps avoid superfluous GCs when running

  // applications with very low allocation rate.

  const size_t used_after_last_gc = ZStatHeap::used_at_relocate_end();

  const size_t used_increase_threshold = ZHeap::heap()->soft_max_capacity() * 0.10; // 10%

  const size_t used_threshold = used_after_last_gc + used_increase_threshold;

  const size_t used = ZHeap::heap()->used();

  const double time_since_last_gc = ZStatCycle::time_since_last();

  const double time_since_last_gc_threshold = 5 * 60; // 5 minutes

  if (used < used_threshold && time_since_last_gc < time_since_last_gc_threshold) {

    // Don't even consider doing a proactive GC

    log_debug(gc, director)("Rule: Proactive, UsedUntilEnabled: " SIZE_FORMAT "MB, TimeUntilEnabled: %.3fs",

                            (used_threshold - used) / M,

                            time_since_last_gc_threshold - time_since_last_gc);

    return false;

  }

  const double assumed_throughput_drop_during_gc = 0.50; // 50%

  const double acceptable_throughput_drop = 0.01;        // 1%

  const AbsSeq& duration_of_gc = ZStatCycle::normalized_duration();

  const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);

  const double acceptable_gc_interval = max_duration_of_gc * ((assumed_throughput_drop_during_gc / acceptable_throughput_drop) - 1.0);

  const double time_until_gc = acceptable_gc_interval - time_since_last_gc;

  log_debug(gc, director)("Rule: Proactive, AcceptableGCInterval: %.3fs, TimeSinceLastGC: %.3fs, TimeUntilGC: %.3fs",

                          acceptable_gc_interval, time_since_last_gc, time_until_gc);

  return time_until_gc <= 0;

}

bool ZDirector::rule_high_usage() const {

  // Perform GC if the amount of free memory is 5% or less. This is a preventive

  // meassure in the case where the application has a very low allocation rate,

  // such that the allocation rate rule doesn't trigger, but the amount of free

  // memory is still slowly but surely heading towards zero. In this situation,

  // we start a GC cycle to avoid a potential allocation stall later.

  // Calculate amount of free memory available to Java threads. Note that

  // the heap reserve is not available to Java threads and is therefore not

  // considered part of the free memory.

  const size_t max_capacity = ZHeap::heap()->soft_max_capacity();

  const size_t max_reserve = ZHeap::heap()->max_reserve();

  const size_t used = ZHeap::heap()->used();

  const size_t free_with_reserve = max_capacity - used;

  const size_t free = free_with_reserve - MIN2(free_with_reserve, max_reserve);

  const double free_percent = percent_of(free, max_capacity);

  log_debug(gc, director)("Rule: High Usage, Free: " SIZE_FORMAT "MB(%.1f%%)",

                          free / M, free_percent);

  return free_percent <= 5.0;

}

GCCause::Cause ZDirector::make_gc_decision() const {

  // Rule 0: Timer

  if (rule_timer()) {

    return GCCause::_z_timer;

  }

  // Rule 1: Warmup

  if (rule_warmup()) {

    return GCCause::_z_warmup;

  }

  // Rule 2: Allocation rate

  if (rule_allocation_rate()) {

    return GCCause::_z_allocation_rate;

  }

  // Rule 3: Proactive

  if (rule_proactive()) {

    return GCCause::_z_proactive;

  }

  // Rule 4: High usage

  if (rule_high_usage()) {

    return GCCause::_z_high_usage;

  }

  // No GC

  return GCCause::_no_gc;

}

void ZDirector::run_service() {

  // Main loop

  while (_metronome.wait_for_tick()) {

    sample_allocation_rate();

    const GCCause::Cause cause = make_gc_decision();

    if (cause != GCCause::_no_gc) {

      ZCollectedHeap::heap()->collect(cause);

    }

  }

}

void ZDirector::stop_service() {

  _metronome.stop();

}