bug: ScheduleOnce() doesn't always trigger

[TrueBrain]

Bug description
ScheduleOnce doesn't always trigger. Sometimes it works 10 times, sometimes 20. But it always sometimes doesn't trigger.

In my use-case, I have an actor that needs to do some task once in a while (but not on a regular interval). So I use ScheduleOnce to schedule the task, and if it needs be, it uses ScheduleOnce to schedule the next task (until all tasks are done).

How to reproduce it?
See this gist. It is basically goakt-actor-hello-world, but the Receive sets a ScheduleOnce. It should keep itself going till the end of time.

However, after ~20 seconds (sometimes earlier, sometimes later) it stops. Without any error, from what I can tell.

Expected behavior
Have a ScheduleOnce that schedules a message (once) reliable, if no error was returned.

Library Version:

• Go-Akt version: 1b11cfd
• Go version: 1.25.3

Additional context

[TrueBrain]

Schedule seems to have a similar problem, where sometimes it just skips a few calls.

{"level":"info","ts":"2025-12-27T11:36:47.949558+0100","caller":"goakt/test.go:96","msg":"HelloWorld received a TestPing message"}
{"level":"info","ts":"2025-12-27T11:36:48.950256+0100","caller":"goakt/test.go:96","msg":"HelloWorld received a TestPing message"}
{"level":"info","ts":"2025-12-27T11:36:53.267042+0100","caller":"goakt/test.go:96","msg":"HelloWorld received a TestPing message"}
{"level":"info","ts":"2025-12-27T11:36:54.267049+0100","caller":"goakt/test.go:96","msg":"HelloWorld received a TestPing message"}

I was calling it on a 1s interval, but here for 4 seconds there was no call. But as it is an interval, it does "recover". The docs also mention for Schedule that This function does not provide built-in delivery guarantees such as at-least-once or exactly-once semantics; ensure idempotency where needed..

Does ScheduleOnce suffer the same condition?

[Tochemey]

ScheduleOnce fires once and ends. It is one time trigger. If you want to schedule message continuously use the other schedule methods with cron expression. Moreover the godoc of the function did specify the behavior of the function.

[TrueBrain]

Exactly! :)

I expect ScheduleOnce to fire once, but as the gist above shows: sometimes it actually doesn't fire at all. Which made me wonder if ScheduleOnce has the same condition as Schedule, and in fact doesn't guarantee at-least-once? ScheduleOnce doesn't mention that.

If ScheduleOnce doesn't guarantee at-least-once, it means I can't use the scheduling system at all. Not a problem, I can just roll my own. But it did surprise me, so mostly wondering if my observations are correct :)

[Tochemey]

I will need to investigate why it did not fire at all in the gist because there are unit tests around the scheduler code path.