Make a promise-returning function as non-overlapping one.

child.js

process.on('message', function(message) {
  console.log("message received", message);
  process.send(message.toUpperCase(), function(err) {
    console.log("replied");
  });
});

parent.js

var cp = require('child_process');

var child = cp.fork('child.js');

function send(...msg) {
  return new Promise((res, rej) => {
    child.send(msg.join(""), (err) => {
      if (err) rej(err);
      else res();
    });
  });
}

function recv() {
  return new Promise((res, rej) => {
    child.once('message', (message) => {
      res(message);
    })
  });
}

function atomic(inner) {
  var obj = {};
  return (...args) => new Promise((resolve, reject) => {
    const transact = () => {
      obj.locked = true; // take this chance
      inner(...args)
        .then(resolve, reject)
        .then(() => {
          obj.locked = false; // release
        });
    };
    if (obj.locked) {
      var observer = () => {
        if (obj.locked)
          return; // wakeup later, then wait for next chance
        else {
          Object.unobserve(obj, observer);
          transact();
        }
      };
      Object.observe(obj, observer);
    } else {
      transact();
    }
  });
}

const write = atomic((...msg) => send(...msg).then(recv));

Promise.all([write("abc", "def"), write("def"), write("ghi")])
  .then(result => console.log(result))
  .then(() => console.log("done"))
  .then(() => child.kill())