src/hotspot/share/gc/shenandoah/shenandoahRegulatorThread.cpp

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 * 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
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#include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
#include "gc/shenandoah/mode/shenandoahMode.hpp"
#include "gc/shenandoah/shenandoahAsserts.hpp"
#include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
#include "gc/shenandoah/shenandoahHeap.inline.hpp"
#include "gc/shenandoah/shenandoahOldGeneration.hpp"
#include "gc/shenandoah/shenandoahRegulatorThread.hpp"
#include "gc/shenandoah/shenandoahYoungGeneration.hpp"
#include "logging/log.hpp"

ShenandoahRegulatorThread::ShenandoahRegulatorThread(ShenandoahGenerationalControlThread* control_thread) :
  _heap(ShenandoahHeap::heap()),
  _control_thread(control_thread),
  _sleep(ShenandoahControlIntervalMin),
  _last_sleep_adjust_time(os::elapsedTime()) {
  shenandoah_assert_generational();
  _old_heuristics = _heap->old_generation()->heuristics();
  _young_heuristics = _heap->young_generation()->heuristics();
  _global_heuristics = _heap->global_generation()->heuristics();

  set_name("Shenandoah Regulator Thread");
  create_and_start();
}

void ShenandoahRegulatorThread::run_service() {
  if (ShenandoahAllowOldMarkingPreemption) {
    regulate_young_and_old_cycles();
  } else {
    regulate_young_and_global_cycles();
  }

  log_debug(gc)("%s: Done.", name());
}

void ShenandoahRegulatorThread::regulate_young_and_old_cycles() {
  while (!should_terminate()) {
    ShenandoahGenerationalControlThread::GCMode mode = _control_thread->gc_mode();
    if (mode == ShenandoahGenerationalControlThread::none) {
      if (should_start_metaspace_gc()) {
        if (request_concurrent_gc(_heap->global_generation())) {
          // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
          _global_heuristics->log_trigger("%s", GCCause::to_string(GCCause::_metadata_GC_threshold));
          _global_heuristics->cancel_trigger_request();
        }
      } else {
        if (_old_heuristics->should_resume_old_cycle()) {
          if (request_concurrent_gc(_heap->old_generation())) {
            _old_heuristics->cancel_trigger_request();
            log_debug(gc)("Heuristics request to resume old collection accepted");
          }
        } else if (start_old_cycle()) {
          log_debug(gc)("Heuristics request for old collection accepted");
          _young_heuristics->cancel_trigger_request();
          _old_heuristics->cancel_trigger_request();
        } else if (start_young_cycle()) {
          log_debug(gc)("Heuristics request for young collection accepted");
          _young_heuristics->cancel_trigger_request();
        }
      }
    } else if (mode == ShenandoahGenerationalControlThread::servicing_old) {
      if (start_young_cycle()) {
        log_debug(gc)("Heuristics request to interrupt old for young collection accepted");
        _young_heuristics->cancel_trigger_request();
      }
    }

    regulator_sleep();
  }
}


void ShenandoahRegulatorThread::regulate_young_and_global_cycles() {
  while (!should_terminate()) {
    if (_control_thread->gc_mode() == ShenandoahGenerationalControlThread::none) {
      if (start_global_cycle()) {
        log_debug(gc)("Heuristics request for global collection accepted.");
        _global_heuristics->cancel_trigger_request();
      } else if (start_young_cycle()) {
        log_debug(gc)("Heuristics request for young collection accepted.");
        _young_heuristics->cancel_trigger_request();
      }
    }

    regulator_sleep();
  }
}

void ShenandoahRegulatorThread::regulator_sleep() {
  // Wait before performing the next action. If allocation happened during this wait,
  // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
  // back off exponentially.
  double current = os::elapsedTime();

  if (ShenandoahHeap::heap()->has_changed()) {
    _sleep = ShenandoahControlIntervalMin;
  } else if ((current - _last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
    _sleep = MIN2<uint>(ShenandoahControlIntervalMax, MAX2(1u, _sleep * 2));
    _last_sleep_adjust_time = current;
  }

  os::naked_short_sleep(_sleep);
  if (LogTarget(Debug, gc, thread)::is_enabled()) {
    double elapsed = os::elapsedTime() - current;
    double hiccup = elapsed - double(_sleep);
    if (hiccup > 0.001) {
      log_debug(gc, thread)("Regulator hiccup time: %.3fs", hiccup);
    }
  }
}

bool ShenandoahRegulatorThread::start_old_cycle() const {
  return _old_heuristics->should_start_gc() && request_concurrent_gc(_heap->old_generation());
}

bool ShenandoahRegulatorThread::start_young_cycle() const {
  return _young_heuristics->should_start_gc() && request_concurrent_gc(_heap->young_generation());
}

bool ShenandoahRegulatorThread::start_global_cycle() const {
  return _global_heuristics->should_start_gc() && request_concurrent_gc(_heap->global_generation());
}

bool ShenandoahRegulatorThread::request_concurrent_gc(ShenandoahGeneration* generation) const {
  double now = os::elapsedTime();
  bool accepted = _control_thread->request_concurrent_gc(generation);
  if (LogTarget(Debug, gc, thread)::is_enabled() && accepted) {
    double wait_time = os::elapsedTime() - now;
    if (wait_time > 0.001) {
      log_debug(gc, thread)("Regulator waited %.3fs for control thread to acknowledge request.", wait_time);
    }
  }
  return accepted;
}

void ShenandoahRegulatorThread::stop_service() {
  log_debug(gc)("%s: Stop requested.", name());
}

bool ShenandoahRegulatorThread::should_start_metaspace_gc() {
  // The generational mode can, at present, only unload classes during a global
  // cycle. For this reason, we treat an oom in metaspace as a _trigger_ for a
  // global cycle. But, we check other prerequisites before starting a gc that won't
  // unload anything.
  return ClassUnloadingWithConcurrentMark
      && _global_heuristics->can_unload_classes()
      && _global_heuristics->has_metaspace_oom();
}