What happens to a timer created with a deadline in the past?

logan_saso · April 10, 2024, 9:05pm

Using the Go SDK, we had a situation where an activity gives back a timestamp that it wants to run again. If the timestamp is set we create new timer for timeWeWantToRun.Sub(workflow.Now(ctx))

What happens if the activity takes awhile to finish and passes back a timeWeWantToRun in the past? Experimentally it seems like the timer never fires / the selector hangs sleeping forever. But intuitively I thought it would just have auto-fired immediately when a selector runs. What part am I not understanding?

maxim · April 11, 2024, 9:29pm

The timer that receives 0 or negative delay fires immediately without creating a server-side timer.

github.com

temporalio/sdk-go/blob/108aac8c41090c35910d9a8fc545865807d725b4/internal/workflow.go#L1153


      
          // timer by cancel the Context (using context from workflow.WithCancel(ctx)) and that will cancel the timer. After timer
          // is canceled, the returned Future become ready, and Future.Get() will return *CanceledError.
          func NewTimer(ctx Context, d time.Duration) Future {
          	assertNotInReadOnlyState(ctx)
          	i := getWorkflowOutboundInterceptor(ctx)
          	return i.NewTimer(ctx, d)
          }
          
          func (wc *workflowEnvironmentInterceptor) NewTimer(ctx Context, d time.Duration) Future {
          	future, settable := NewFuture(ctx)
          	if d <= 0 {
          		settable.Set(true, nil)
          		return future
          	}
          
          	ctxDone, cancellable := ctx.Done().(*channelImpl)
          	cancellationCallback := &receiveCallback{}
          	timerID := wc.env.NewTimer(d, func(r *commonpb.Payloads, e error) {
          		settable.Set(nil, e)
          		if cancellable {
          			// future is done, we don't need cancellation anymore

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What happens to a timer created with a deadline in the past?

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