v8/src/heap/gc-idle-time-handler.h

// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_HEAP_GC_IDLE_TIME_HANDLER_H_
#define V8_HEAP_GC_IDLE_TIME_HANDLER_H_

#include "src/globals.h"

namespace v8 {
namespace internal {

enum GCIdleTimeActionType {
  DONE,
  DO_NOTHING,
  DO_INCREMENTAL_STEP,
  DO_FULL_GC,
};


class GCIdleTimeAction {
 public:
  static GCIdleTimeAction Done() {
    GCIdleTimeAction result;
    result.type = DONE;
    result.additional_work = false;
    return result;
  }

  static GCIdleTimeAction Nothing() {
    GCIdleTimeAction result;
    result.type = DO_NOTHING;
    result.additional_work = false;
    return result;
  }

  static GCIdleTimeAction IncrementalStep() {
    GCIdleTimeAction result;
    result.type = DO_INCREMENTAL_STEP;
    result.additional_work = false;
    return result;
  }

  static GCIdleTimeAction FullGC() {
    GCIdleTimeAction result;
    result.type = DO_FULL_GC;
    result.additional_work = false;
    return result;
  }

  void Print();

  GCIdleTimeActionType type;
  bool additional_work;
};


class GCIdleTimeHeapState {
 public:
  void Print();

  int contexts_disposed;
  double contexts_disposal_rate;
  size_t size_of_objects;
  bool incremental_marking_stopped;
};


// The idle time handler makes decisions about which garbage collection
// operations are executing during IdleNotification.
class V8_EXPORT_PRIVATE GCIdleTimeHandler {
 public:
  // If we haven't recorded any incremental marking events yet, we carefully
  // mark with a conservative lower bound for the marking speed.
  static const size_t kInitialConservativeMarkingSpeed = 100 * KB;

  // Maximum marking step size returned by EstimateMarkingStepSize.
  static const size_t kMaximumMarkingStepSize = 700 * MB;

  // We have to make sure that we finish the IdleNotification before
  // idle_time_in_ms. Hence, we conservatively prune our workload estimate.
  static const double kConservativeTimeRatio;

  // If we haven't recorded any mark-compact events yet, we use
  // conservative lower bound for the mark-compact speed.
  static const size_t kInitialConservativeMarkCompactSpeed = 2 * MB;

  // If we haven't recorded any final incremental mark-compact events yet, we
  // use conservative lower bound for the mark-compact speed.
  static const size_t kInitialConservativeFinalIncrementalMarkCompactSpeed =
      2 * MB;

  // Maximum final incremental mark-compact time returned by
  // EstimateFinalIncrementalMarkCompactTime.
  static const size_t kMaxFinalIncrementalMarkCompactTimeInMs;

  // This is the maximum scheduled idle time. Note that it can be more than
  // 16.66 ms when there is currently no rendering going on.
  static const size_t kMaxScheduledIdleTime = 50;

  // The maximum idle time when frames are rendered is 16.66ms.
  static const size_t kMaxFrameRenderingIdleTime = 17;

  static const int kMinBackgroundIdleTime = 900;

  // An allocation throughput below kLowAllocationThroughput bytes/ms is
  // considered low
  static const size_t kLowAllocationThroughput = 1000;

  // If contexts are disposed at a higher rate a full gc is triggered.
  static const double kHighContextDisposalRate;

  // Incremental marking step time.
  static const size_t kIncrementalMarkingStepTimeInMs = 1;

  static const size_t kMinTimeForOverApproximatingWeakClosureInMs;

  // Number of times we will return a Nothing action in the current mode
  // despite having idle time available before we returning a Done action to
  // ensure we don't keep scheduling idle tasks and making no progress.
  static const int kMaxNoProgressIdleTimes = 10;

  GCIdleTimeHandler() : idle_times_which_made_no_progress_(0) {}

  GCIdleTimeAction Compute(double idle_time_in_ms,
                           GCIdleTimeHeapState heap_state);

  bool Enabled();

  void ResetNoProgressCounter() { idle_times_which_made_no_progress_ = 0; }

  static size_t EstimateMarkingStepSize(double idle_time_in_ms,
                                        double marking_speed_in_bytes_per_ms);

  static double EstimateFinalIncrementalMarkCompactTime(
      size_t size_of_objects, double mark_compact_speed_in_bytes_per_ms);

  static bool ShouldDoContextDisposalMarkCompact(int context_disposed,
                                                 double contexts_disposal_rate);

  static bool ShouldDoFinalIncrementalMarkCompact(
      double idle_time_in_ms, size_t size_of_objects,
      double final_incremental_mark_compact_speed_in_bytes_per_ms);

  static bool ShouldDoOverApproximateWeakClosure(double idle_time_in_ms);

 private:
  GCIdleTimeAction NothingOrDone(double idle_time_in_ms);

  // Idle notifications with no progress.
  int idle_times_which_made_no_progress_;

  DISALLOW_COPY_AND_ASSIGN(GCIdleTimeHandler);
};

}  // namespace internal
}  // namespace v8

#endif  // V8_HEAP_GC_IDLE_TIME_HANDLER_H_