Advanced example of a data loss

test_message_loss_2.js

const cluster = require('cluster');

async function waitForMessage(child) {
  return new Promise(resolve => {
    child.once('message', msg => {
      console.log('Master. waitForMessage. Message is received', msg);
      return resolve();
    });
  });
}

if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);

  const child = cluster.fork();

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

  child.on('message', msg => {
    console.log(`Master. Message observer: ${msg}`);
  });

  child.once('online', async () => {
    console.log('Master. Sending command.');
    child.send('start');

    console.log('Master. Start of await #1.');
    await waitForMessage(child);
    console.log('Master. End of await #1.');

    console.log('Master. Start of await #2.');
    await waitForMessage(child);
    console.log('Master. End of await #2.');

    process.exit(0);
  });
} else {
  console.log(`Worker ${process.pid} started`);

  process.on('message', (msg) => {
    if (msg !== 'start') return;

    process.send('message1');
    process.send('message2');
    process.send('message3');
  });
}

/*
Master 11853 is running
Master. Sending command.
Master. Start of await #1.
Worker 11854 started
Master. Message observer: message1
Master. waitForMessage. Message is received message1
Master. Message observer: message2
Master. Message observer: message3
Master. End of await #1.
Master. Start of await #2.

// hanged up

--------


Master 11860 is running
Master. Sending command.
Master. Start of await #1.
Worker 11861 started
Master. Message observer: message1
Master. waitForMessage. Message is received message1
Master. End of await #1.
Master. Start of await #2.
Master. Message observer: message2
Master. waitForMessage. Message is received message2
Master. Message observer: message3
Master. End of await #2.

Process finished with exit code 0

// executed ok
 */