Understanding infinite loop with selector

Community Support
,
1

I’m not sure I understand Selectors as the following code snippet has led to an infinite loop that I can’t explain why or how it happened (it’s only happened once)

for !state.IsCutoffReached {
    logger.Info("Waiting for cutoff...", "state", state)

    workflow.NewSelector(ctx).
       AddFuture(state.getCutoffTimer(ctx), func(_ workflow.Future) {
          currentEndTime := state.C.EndAt

          c, err := activities.GetBaz(ctx, state.ID)
          if err != nil {
             logger.Error("Failed to refetch baz", "state", state, "error", err)
          }
          state.C = c

          state.IsCutoffReached = !state.C.EndAt.After(currentEndTime)
       }).
       AddReceive(workflow.GetSignalChannel(ctx, workflows.SignalA), func(c workflow.ReceiveChannel, _ bool) {
          signal := workflows.Receive[workflows.Foo](c, ctx)
          state.startChildWorkflows(ctx, signal)
       }).
       AddReceive(workflow.GetSignalChannel(ctx, workflows.SignalB), func(c workflow.ReceiveChannel, _ bool) {
          if !state.IsX {
             signal := workflows.Receive[workflows.Bar](c, ctx)

             state.IsX = true
          }
       }).
       Select(ctx)
}

Basically I’m recreating a selector in a loop as I’m setting a Timer that fires when a specific entity’s (that exists in a separate Postgres DB) end_at is reached. This entity can be updated so when the first Timer fires I check to see if the end_at datetime was updated, if so recreate the selector and wait again.

What happened is I got into an infinite loop where the selector just kept getting recreated with no signal or timers firing.

Thank you.

2

I don’t see anything obvious. Are you sure that getCutoffTimer doesn’t return a timer that already fired? If you create a reproduction we can take a look.

3

I can see the timer continually get recreated with the correct date in the future. e.g. from temporal UI:
”Start To Fire Timeout 1 month, 24 days, 7 hours, 25 minutes, 25 seconds"

And I just see Timer Started

    {
      "eventId": "51191",
      "eventTime": "2025-08-22T21:41:04.379573623Z",
      "eventType": "EVENT_TYPE_TIMER_STARTED",
      "version": "1760",
      "taskId": "652228181",
      "userMetadata": {
        "summary": {
          "metadata": {
            "encoding": "json/plain"
          },
          "data": "campaign-cutoff-timer"
        }
      },
      "timerStartedEventAttributes": {
        "timerId": "51191",
        "startToFireTimeout": "4778335.642158254s",
        "workflowTaskCompletedEventId": "51190"
      }
    },
4

I think this is the culprit. The callback is called, but the signal is not consumed, so the next call to Select calls this callback again.

5

Would it be correct to do this instead then if I still only want to do whats in the conditional once even if the signal occurs N times?

ddReceive(workflow.GetSignalChannel(ctx, workflows.SignalB), func(c workflow.ReceiveChannel, _ bool) {
          signal := workflows.Receive[workflows.Bar](c, ctx)
          if !state.IsX {
             ...
             state.IsX = true
          }
       }).
6

Yes, that works.

7

That makes sense, thank you!