Fs Async Pool

Non-blocking fs on the thread pool: binary writes and the classic callback form both run off the event-loop thread now.

Two things this demonstrates: 1. A binary body (a Uint8Array, embedded NUL and all) writes out whole via fs.promises.writeFile / appendFile — pooled, not inline. 2. The callback form fs.readFile(path, cb) is genuinely non-blocking: the code after the call runs before the callback, and a 0 ms timer scheduled alongside it may fire first or not (the read's pool round trips race the timer, in Node too).

import fs from 'fs';

const path = '/tmp/klain_fs_async_pool_example.bin';

async function main(): Promise<void> {
  // 1. Binary write + append, then read back. "AB\0CD" then "EF" → 7 bytes.
  await fs.promises.writeFile(path, new Uint8Array([65, 66, 0, 67, 68]));
  await fs.promises.appendFile(path, new Uint8Array([69, 70]));
  const back: string = await fs.promises.readFile(path, "utf8");
  console.log('bytes written: ' + back.length);

  // 2. Callback form, non-blocking: the caller carries on first.
  let after: boolean = false;
  setTimeout(() => {}, 0);
  fs.readFile(path, "utf8", (err, data) => {
    console.log('callback read: ' + data.length + ' bytes');
    console.log('read was non-blocking: ' + after);
    fs.unlink(path, (e) => { console.log('cleaned up'); });
  });
  after = true;
}

main();

View source on GitHubexamples/fs/fs_async_pool.ts

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