Node.js: Race condition when receiving data on tcp socket

Question

I'm using the net library of Node.js to conect to a server that is publishing data. So I'm listening for 'data'-events on client side. When the data-event is fired, I append the received data to my rx-buffer and check if we got a complete message by reading some bytes. If I got a valid message, I remove the message from the buffer and process it. The source code looks like:

rxBuffer = ''

client.on('data', (data) => {
  rxBuffer += data

  // for example... 10 stores the message length...
  while (rxBuffer.length > 10 && rxBuffer.length >= (10 + rxBuffer[10])) {
    const msg = rxBuffer.slice(0, 10 + rxBuffer[10])
    rxBuffer = rxBuffer.slice(0, msg.length) // remove message from buffer
    processMsg(msg) // process message..
  }
})

As far as I know that the typical way. But... what happens if the data event fired multiple times? So, imagine I'm getting a data event and while I append the data to my rx-buffer I'm getting the next data event. So the "new" data event will also append the data to the rxBuffer and starts my while-loop. So I've two handlers that are processing the same messages because they share the same rx-buffer. Is this correct? How can I handle this? In other languages I'd say use something like a mutex to prevent multiple access to the rx-buffer... but what's the solution forjs?!?! Or maybe I'm wrong and I'm never getting multiple data-events while one event is still active? Any ideas?

Answer 1

JavaScript is single threaded. The second event will not run until the first one either completes or blocks, the latter of which could presumably happen in your processMsg() . If that's the case, multiple executions of processMsg() could be interleaved. If they aren't changing any global data ( rxBuffer included), then you shouldn't have a problem.