Buffer pool usage tracker

track-buffer-pool-usage.js

'use strict';
const orig = Buffer.allocUnsafe;

const stats = {
  inUse: 0,
  allocated: 0
};

const group = new FinalizationGroup((holdings) => {
  for (const info of holdings) {
    if (info.type === 'Buffer') {
      stats.inUse -= info.length;
    } else {
      stats.allocated -= info.length;
    }
  }

  log();
});

const kSeen = Symbol('kSeen');

Buffer.allocUnsafe = (...args) => {
  const ret = orig(...args);

  if (ret.buffer.byteLength === ret.length) return ret;

  if (!ret.buffer[kSeen]) {
    ret.buffer[kSeen] = true;

    const info = {
      type: 'ArrayBuffer',
      length: ret.buffer.byteLength
    };

    stats.allocated += ret.buffer.byteLength;
    group.register(ret.buffer, info);
  }

  {
    const info = {
      type: 'Buffer',
      length: ret.length
    };

    stats.inUse += ret.length;
    group.register(ret, info);
  }

  log();

  return ret;
}

const allocationLog = [];

function log() {
  allocationLog.push({ ts: process.hrtime.bigint(), ...stats });
}
log();

function getUsageRatio() {
  log();

  const integratedStats = {
    inUse: 0,
    allocated: 0
  };

  for (let i = 0; i < allocationLog.length - 1; i++) {
    const dur = Number(allocationLog[i + 1].ts - allocationLog[i].ts);
    integratedStats.inUse += allocationLog[i].inUse * dur;
    integratedStats.allocated += allocationLog[i].allocated * dur;
  }

  return integratedStats.inUse / integratedStats.allocated;
}

process.on('exit', () => {
  console.log('Usage ratio: ', getUsageRatio().toFixed(5));
});