clobber.mjs

// node clobber.mjs -> demonstrate common filesystem anti-pattern that creates race conditions
// node clobber.mjs safe -> demonstrate safe filesystem manipulation

import cluster from 'cluster';
import process from 'process';
import fs from 'fs';
import path from 'path';
import { fileURLToPath } from 'url';

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const concurrency = 100;
const directory = path.resolve(__dirname, 'foobar');
const safe = process.argv[2] === 'safe';
const createDir = safe ? createDirSafely : createDirUnsafely;

if (cluster.isPrimary) {
  console.log(`Primary ${process.pid} is running, safe?`, safe);

  cluster.on('exit', (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`);
    process.exit(1);
  });

  setTimeout(() => {
    for (let i = 0; i < concurrency; i++) cluster.fork();
  }, 1000);
}
else {
  setInterval(() => {
    Math.random() < 0.5 ? createDir() : destroyDir();
  }, 100);
}

function createDirUnsafely() {
    // this appears to guarantee that the directory doesn't exist,
    // but it's not possible to hold that guarantee through to the subsequent write
    if (fs.existsSync(directory)) return;
    fs.mkdirSync(directory);
    console.log('created directory');
}

function createDirSafely() {
    try {
        // notice that no exists check is necessary
        fs.mkdirSync(directory, { recursive: true });
        console.log('created directory');
    } catch (err) {
        console.log('failed to create directory');
    }
}

function destroyDir() {
    try {
        fs.rmSync(directory, { recursive: true });
    } catch (err) {}
}