42912: Channel enumeration already in progress

A request to enumerate the channels active in an app was rejected because another enumeration was already running. Only one channel enumeration can run at a time for an app.

What you should do

Wait for the in-progress enumeration to finish before starting another, since only one can run at a time. If your application makes these requests from more than one place, coordinate them so they do not overlap, or retry after a short delay.

Why it happens

Enumerating the channels active in an app is an expensive operation, so Ably allows only one to run at a time for a given app. A request that arrives while another enumeration is still in progress is rejected rather than queued.

What you'll see

The request is rejected. The error is reported with code 42912 and HTTP status 429, with a message of the form Channel iteration call already in progress. Only 1 call(s) may be executed concurrently. "Iteration" here is the internal term for channel enumeration.