event_loop_delays_monitor.ts

/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

import type { IntervalHistogram as PerfIntervalHistogram } from 'perf_hooks';
import { monitorEventLoopDelay } from 'perf_hooks';
import type { IntervalHistogram } from '../types';

export class EventLoopDelaysMonitor {
  private readonly loopMonitor: PerfIntervalHistogram;
  private fromTimestamp: Date;

  /**
   * Creating a new instance from EventLoopDelaysMonitor will
   * automatically start tracking event loop delays.
   */
  constructor() {
    const monitor = monitorEventLoopDelay();
    monitor.enable();
    this.fromTimestamp = new Date();
    this.loopMonitor = monitor;
  }
  /**
   * Collect gathers event loop delays metrics from nodejs perf_hooks.monitorEventLoopDelay
   * the histogram calculations start from the last time `reset` was called or this
   * EventLoopDelaysMonitor instance was created.
   * @returns {IntervalHistogram}
   */
  public collect(): IntervalHistogram {
    const lastUpdated = new Date();
    this.loopMonitor.disable();
    const { min, max, mean, exceeds, stddev } = this.loopMonitor;

    const collectedData: IntervalHistogram = {
      min,
      max,
      mean,
      exceeds,
      stddev,
      fromTimestamp: this.fromTimestamp.toISOString(),
      lastUpdatedAt: lastUpdated.toISOString(),
      percentiles: {
        50: this.loopMonitor.percentile(50),
        75: this.loopMonitor.percentile(75),
        95: this.loopMonitor.percentile(95),
        99: this.loopMonitor.percentile(99),
      },
    };

    this.loopMonitor.enable();
    return collectedData;
  }

  /**
   * Resets the collected histogram data.
   */
  public reset() {
    this.loopMonitor.reset();
    this.fromTimestamp = new Date();
  }

  /**
   * Disables updating the interval timer for collecting new data points.
   */
  public stop() {
    this.loopMonitor.disable();
  }
}