[Bug] Cancel in pickfirst sample is not working about samples-go

[chongkai]

Mentioned in https://pkg.go.dev/go.temporal.io/[email protected]/activity,

Currently cancellation is delivered only to Activities that call RecordHeartbeat.

Is this the cause?

[dnr]

The sample code is calling RecordHeartbeat, though, so that's not quite the problem. What appears to be happening is that cancellation is only delivered when a heartbeat is actually sent, and the sdk does batching of heartbeats internally, so that a call to activity.RecordHeartbeat doesn't necessarily send a heartbeat. The batching is based on the value of HeartbeatTimeout.

You can see this by changing the duration of f1 to 60 seconds instead of 5 seconds: the activity will be cancelled after around 8 seconds (with HeartbeatTimeout set to 10 seconds). If you increase HeartbeatTimeout it'll take longer, and if you decrease it, the cancellation will be delivered sooner. You can see the logic here: https://github.com/temporalio/sdk-go/blob/1ec44328977e7bb896d2d405a8f1334120df282a/internal/internal_task_handlers.go#L1628

So this doesn't seem like a bug, though there's probably room to improve the documentation.

[chongkai]

Thanks @dnr for your clarification! However, these internals seem a bit obscure to new comers. I submitted a PR (#111) in hopes that it could help others better understand the sample. If it doesn't fit the purpose of the sample, please let me know.