How can I handle pm2 cron jobs that run longer than the cron interval?

I have a cron job running on pm2 that sends notifications on a 5 second interval. Although it should never happen, I'm concerned that the script will take longer than 5 seconds to run. Basically, if the previous run takes 6 seconds, I don't want to start the next run until the first one finishes. Is there a way to handle this solely in pm2? Everything I've found says to use shell scripting to handle it, but it's not nearly as easy to replicate and move to new servers when needed.

As of now, I have the cron job just running in a never ending while loop (unless there's an error) that waits up to 5 seconds at the end. If it errors, it exits and reports the error, then restarts because it's running via pm2. I'm not too excited about this implementation though. Are there other options?

edit for clarification of my current logic -

function runScript() {
  while (!err) {
    // do stuff
    wait(5 seconds - however long 'do stuff' took) // if it took 1 second to 'do stuff', then it waits 4 seconds
  }
}

runScript()

This feels like a hacky way to get around the cron limits of pm2. It's possible that I'm just being paranoid... I just wanna make sure I'm not using antipatterns.

Solution

What do you mean you have the cron job running in a while loop? PM2 is starting a node process which contains a never-ending while loop that waits 5 seconds? Your implementation of a cron seems off to me, maybe you could provide more details.

Instead of a cron, I would use something like setTimeout method. Run your script using PM2 and in the script is a method like such:

function sendMsg() {
  // do the work

  setTimeout(sendMsg, 5000); // call sendMsg after waiting 5 seconds
}

sendMsg();

By doing it this way, your sendMsg function can take all the time it needs to run, and the next call will start 5 seconds after that. PM2 will restart your application if it crashes.

If you're looking to do it at specific 5 second intervals, but only when the method is not running, simply add a tracking variable to the equation, something like:

let doingWork = false;

function sendMsg() {
  if (!doingWork) {
    doingWork = true;
    // do the work
    doingWork = false;
  }
}

setInterval(sendMsg, 5000); // call sendMsg every 5 seconds

You could replace setInterval with PM2 cron call on the script, but the variable idea remains the same.