loadmill-monitor/lib/sampler.js

Performance monitoring for Node.js

class Sampler {
  constructor (sampleDelay, maxSamples) {
    this.samples = [];
    this.sampleDelay = sampleDelay || 1000;
    this.maxSamples = maxSamples || 10000;
  }

  sampleUntil(stopTime, onSample) {
    const now = Date.now();

    if (stopTime <= now) {
      this.stopSampling();
      return;
    }

    this.stopTime = stopTime;
    this.onSample = onSample;

    if (!this.sampleTimer) {
      this.lastPopTime = now;
      this.previousSampleTime = now;
      this.previousCpuUsage = process.cpuUsage();

      this.sampleTimer = setInterval(this._recordSample.bind(this), this.sampleDelay);
      this.sampleTimer.unref();
    }
  }

  popSamples() {
    this.lastPopTime = Date.now();

    const samples = this.samples;
    this.samples = [];
    return samples;
  }

  stopSampling() {
    if (this.sampleTimer) {
      clearInterval(this.sampleTimer);
      this.sampleTimer = null;

      this.samples = [];
    }
  }

  _recordSample() {
    const timestamp = Date.now();

    if (timestamp >= this.stopTime) {
      this.stopSampling();
      return;
    }

    const duration = timestamp - this.previousSampleTime;
    this.previousSampleTime = timestamp;

    const cpuUsage = process.cpuUsage(this.previousCpuUsage);
    this.previousCpuUsage = process.cpuUsage();

    const memoryUsage = process.memoryUsage();

    this.samples.push({
      duration,
      timestamp,

      cpuUsage,
      memoryUsage,
    });

    if (this.samples.length >= this.maxSamples) {
      this.samples = this.samples.slice(Math.floor(this.samples.length / 2));
    }

    if (this.onSample) {
      this.onSample();
    }
  }
}

module.exports = Sampler;