Ability to change retry() params from the task?

[eexit]

Hello,

I would like to know if it'd be possible to be able to update the times argument of the retry() from the task?
For instance, I would like to be able to increase the interval value as the attempt count increases or trim down the attempt count to 0 when a particular error occurred (in order to avoid unnecessary doomed attempts).

Example:

var opts = {
    times: 3,
    interval: 500
};

async.retry(opts, function (callback) {
    someCall(function(err) {
        if (err) {
            switch (err.code) {
                case 'Code1':
                    opts.interval += 500; // Increases the interval for next attempt
                    return callback(err);
                case 'Code2':
                    opts.times = 0; // Avoid other attempts
                    return callback(err);
                default:
                    return callback(err);
            }
        }

        callback();
    });
}, function (err) {
    // Some code
});

Any idea or workaround?

Thanks,

[aearly]

Unfortunately, there's no way to change the retry options after the fact right now -- we copy the options to a new object internally.

To exit early, you could callback with a null error, and some sort of sentinel object you handle specially, but it's kind of a hack.

I'd love to think of a clean way to support customizing the times and interval -- perhaps a function that is called for each iteration to get the times/interval. This would more easily enable things like exponential backoff and early exits.

function getNextInterval(prevInterval, remaningTimes, lastError) {
  if (prevInterval == null) {
    // initial iteration
    return {
      interval: 100,
      times: 5
    };   
  }
  if (lastError && lastError.code === "foo") {
    // exit early
    return {
      times: 0
    };
  }
  // exponential backoff
  return {
    interval: lastInterval * 2,
    times: times - 1
  };
}

async.times(getNextInterval, worker, done);

[eexit]

Thanks @aearly! I'll try this eventually and see how it behaves...

[murdockcrc]

Could we implement the interval parameter to support an array of ints? These ints will be used when the attempts array gets built with the timeout functions that provide the execution delay between retries. I know it does not solve the original request (to change the parameters on the fly), but I am working under the assumption that you don't necessarily need to decide the retry backoff times at runtime.

Obviously, if the passed parameter for interval is not an array but an Int, then we use that as the timeout for all the retries.

[aearly]

Hmmn, perhaps we could make the retry opts more polymorphic -- if you pass an array for the interval, it uses those numbers for each delay interval in sequence.

[aearly]

I think the behavior added in #1161 should be good enough for now.