src/hotspot/share/gc/g1/g1PeriodicGCTask.cpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * version 2 for more details (a copy is included in the LICENSE file that
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#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1ConcurrentMark.inline.hpp"
#include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
#include "gc/g1/g1GCCounters.hpp"
#include "gc/g1/g1PeriodicGCTask.hpp"
#include "gc/shared/suspendibleThreadSet.hpp"
#include "logging/log.hpp"
#include "runtime/globals.hpp"
#include "runtime/os.hpp"
#include "utilities/globalDefinitions.hpp"

bool G1PeriodicGCTask::should_start_periodic_gc(G1CollectedHeap* g1h,
                                                G1GCCounters* counters) {
  // Ensure no GC safepoints while we're doing the checks, to avoid data races.
  SuspendibleThreadSetJoiner sts;

  // If we are currently in a concurrent mark we are going to uncommit memory soon.
  if (g1h->concurrent_mark()->cm_thread()->in_progress()) {
    log_debug(gc, periodic)("Concurrent cycle in progress. Skipping.");
    return false;
  }

  // Check if enough time has passed since the last GC.
  uintx time_since_last_gc = (uintx)g1h->time_since_last_collection().milliseconds();
  if ((time_since_last_gc < G1PeriodicGCInterval)) {
    log_debug(gc, periodic)("Last GC occurred %zums before which is below threshold %zums. 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;
  }

  // Record counters with GC safepoints blocked, to get a consistent snapshot.
  // These are passed to try_collect so a GC between our release of the
  // STS-joiner and the GC VMOp can be detected and cancel the request.
  *counters = G1GCCounters(g1h);
  return true;
}

void G1PeriodicGCTask::check_for_periodic_gc() {
  // If disabled, just return.
  if (G1PeriodicGCInterval == 0) {
    return;
  }

  log_debug(gc, periodic)("Checking for periodic GC.");
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  G1GCCounters counters;
  if (should_start_periodic_gc(g1h, &counters)) {
    if (!g1h->try_collect(GCCause::_g1_periodic_collection, counters)) {
      log_debug(gc, periodic)("GC request denied. Skipping.");
    }
  }
}

G1PeriodicGCTask::G1PeriodicGCTask(const char* name) :
  G1ServiceTask(name) { }

void G1PeriodicGCTask::execute() {
  check_for_periodic_gc();
  // G1PeriodicGCInterval is a manageable flag and can be updated
  // during runtime. If no value is set, wait a second and run it
  // again to see if the value has been updated. Otherwise use the
  // real value provided.
  schedule(G1PeriodicGCInterval == 0 ? 1000 : G1PeriodicGCInterval);
}