spread(
  () => {}, // <-- Process logic.
  (worker, code, signal) => {} // <-- Called on 'exit'.
)

// A simple example
import spread from 'cluster-spread';

spread(() => {
  console.log(process.pid);
  // Make sure to call process.exit() otherwise it will hang.
  process.exit(0);
}, worker => {
  console.log('Done ' + worker.process.pid);
})