fs: add WriteStream.prototype.fsync #28513

const fs = require('fs');
const ws = fs.createWriteStream('test.txt');
ws.write('important data', () => {
  fs.fsync(ws.fd, () => {
    // only now is it safe again to call ws.write()
    ws.write('more important data', () => {
      fs.fsync(ws.fd, () => { /* etc. */ });
    });
  });
});

const ws = require('fs').createWriteStream('test.txt');
ws.write('important data');
ws.fsync();
ws.write('more important data');
ws.fsync();

const util = require('util');
const fs = require('fs');
const ws = fs.createWriteStream('test.txt');
ws.once('open', (fd) => go(fd));
async function go(fd) {
  const write = util.promisify(ws.write.bind(ws));
  const fsync = util.promisify(fs.fsync.bind(null, fd));
  await write('important data');
  await fsync();
  await write('more important data');
  await fsync();
}