gc.js

#!/usr/bin/env node
// call using --inspect brk, GC using memory tab of devtools
// call globalThis.tick() to move the code along and see when things reap from
// manually calling GC
{
  const registry = new FinalizationRegistry((_) => console.log(_, 'reaped'));
  let EASY_TO_FIND = class EASY_TO_FIND2 {
    big = new Uint8Array(1024 * 1024 * 10);
    constructor(_) {
      registry.register(this, _);
    }
  };
  function fn() {
    let a = new EASY_TO_FIND('fn');
    let tasks = [() => ({ fn: a }), () => a = null, () => {}];
    return {
      next() {
        let handler = tasks.shift();
        console.log('fn', `${handler}`)
        if (handler) return { value: handler(), done: false };
        return { value: undefined, done: true };
      },
    };
  }
  function generator() {
    let iter = (function* generator() {
      let a = new EASY_TO_FIND('generator');
      yield { generator: a };
      console.log('no more generator refs');
      yield null;
      console.log('generator still has no refs');
      yield null;
      console.log('generator closing');
      return;
    })();
    iter.next();
    return iter;
  }
  function async() {
    /**
     * @type {Array<Function | null>}
     */
    let ret = [null, null];
    new Promise((f) => {
      ret[0] = f;
    });
    new Promise((f) => {
      ret[1] = f;
    });
    new Promise((f) => {
      ret[2] = f;
    });
    (async function async() {
      let a = new EASY_TO_FIND('async');
      await Promise.all([{ async: a }, ret[0]]);
      console.log('no more async refs');
      await ret[1];
      console.log('async manually cleaning');
      a = null;
      await ret[2];
      console.log('async closing');
      return;
    })();
    return {
      next() {
        let handler = ret.shift();
        if (handler) return { value: handler(), done: false };
        return { value: undefined, done: true };
      },
    };
  }
  console.log('init');
  let cbs = fn();
  let iter = generator();
  let proms = async();
  let ticks = 1;
  function tick() {
    console.log('starting tick', ticks);
    for (let _ of [cbs, iter, proms]) {
      _.next();
    }
    ticks++;
  }
  // manually run tick() from devtools!
  globalThis.tick = tick;
  setInterval(() => {}, 1e4);
}