Changing the Uber Cadence Sleep time based on external (e.g. user) input

Question

Is there an example of a Cadence workflow changing the sleep duration based on external input?

The scenario I'm looking for is this: the workflow goes into sleep until time X but after the sleep starts but before it completes, there is an external trigger that causes time X to change to time Y. Y can either be later or earlier than X. It can even be earlier than "now", which should release the sleep immediately.

Answer 1

Here is code snippet for what you are looking for

func SampleTimerWorkflow(ctx workflow.Context, timerDelay time.Duration) error 
{
    logger := workflow.GetLogger(ctx)
    resetCh := workflow.GetSignalChannel(ctx, "reset")

    timerFired := false
    delay := timerDelay
    for ;!timerFired; {
        selector := workflow.NewSelector(ctx)

        logger.Sugar().Infof("Setting up a timer to fire after: %v", delay)
        timerCancelCtx, cancelTimerHandler := workflow.WithCancel(ctx)
        timerFuture := workflow.NewTimer(timerCancelCtx, delay)
        selector.AddFuture(timerFuture, func(f workflow.Future) {
            logger.Info("Timer Fired.")
            timerFired = true
        })

        selector.AddReceive(resetCh, func(c workflow.Channel, more bool) {
            logger.Info("Reset signal received.")
            logger.Info("Cancel outstanding timer.")
            cancelTimerHandler()

            var t int
            c.Receive(ctx, &t)
            logger.Sugar().Infof("Reset delay: %v seconds", t)
            delay = time.Second * time.Duration(t)
        })

        logger.Info("Waiting for timer to fire.")
        selector.Select(ctx)
    }

    workflow.GetLogger(ctx).Info("Workflow completed.")
    return nil
}

Now you can send a signal to reset the timer to 10 seconds like below:

cadence-cli --domain <domain> wf signal -w <workflow_id>  --name reset --input 10