semaphore over amqp (POC)

index.js

const amqp = require('amqplib/callback_api')
const assert = require('assert')

amqp.connect((err, con) => {
  assert.ifError(err)
  console.log('connected')
  con.createChannel((err, ch) => {
    assert.ifError(err)
    ch.prefetch(1, false)
    ch.assertQueue('Q', {durable: false, autoDelete: true, maxLength: 1}, (err) => {
      assert.ifError(err)
      ch.sendToQueue('Q', Buffer.from(''))
      ch.consume('Q', (msg) => {
        console.log('received from Q:' + JSON.stringify(msg))
        // using a separate channel to guard against RESOURCE-LOCKED (code 405)
        // (which renders channel in-operable and is thrown when exclusive access to Q' cannot be acquired)
        con.createChannel((err, che) => {
          assert.ifError(err)
          che.on('error', (err) => {
            if (err.code === 405) {
              console.log('ACK')
              ch.ack(msg)
            } else {
              throw err
            }
          })
          che.assertQueue('Q\'', {durable: false, autoDelete: true, exclusive: true},
            (err) => !err && eternalWorker())
        })
      }, {noAck: false})
    })
  })
})

function eternalWorker() {
  console.log('doing stuff')
}

npm i amqplib # tested on 0.5.1