FinalizationRegistry test

finalization-registry-test.js

let nextId = 0;
const allocatedObjects = new Map();
const refLossTimes = new Map();

let reportCount = 0;
let reportTime = 0;

const finReg = new FinalizationRegistry((id) => {
  const lossTime = performance.now() - refLossTimes.get(id);
  refLossTimes.delete(id);

  reportCount++;
  reportTime += lossTime;

  console.log(`Reported GC of allocation ${id} ${lossTime}ms after the last reference was removed.`)
});

const intervalId = setInterval(() => {
  // Allocate 4Mb at a time
  const memoryBlock = new ArrayBuffer(1024 * 1024 * 4);
  const id = nextId++;
  allocatedObjects.set(id, memoryBlock);
  finReg.register(memoryBlock, id);

  // Lose the reference one second after creation.
  setTimeout(() => {
    allocatedObjects.delete(id);
    refLossTimes.set(id, performance.now());
  }, 1000);
}, 100);

setTimeout(() => {
  clearInterval(intervalId);
  let oldestLoss = performance.now();

  for (let [key, lossTime] of refLossTimes.entries()) {
    if (lossTime < oldestLoss) {
      oldestLoss = lossTime;
    }
  }

  console.error(`After 2 minues ${refLossTimes.size} reference losses have still been unreported, with the oldest being  ${performance.now() - oldestLoss}ms ago.`);
  console.error(`${reportCount} GCs were reported, with the average time from reference loss to finalizer callback being ${reportTime / reportCount}ms`);
}, 120000);