Orleans AlwaysInterleave question

[jason-bragg]

A few years back and attribute, AlwaysInterleave, was added to Orleans to support Orleankka.

dotnet/orleans#2246

The implementation of this feature allows grain calls attributed with AlwaysInterleave to interleave with other grain calls. However, these calls themselves are not interlaveable and will block a grain like any other grain call. We'd like to change this behavior such that call marked AlwaysInterleave both interleave with other grain calls, but also allows other grain calls to interleave with them. As this feature was added to support orleankka, we wanted to check to see if this change in behavior would violate the expectations of orleankka's usage patterns.

Can someone familiar with these behaviors please advise?
Thanks,
jbragg

[yevhen]

Hi, Jason!

Did you mean MayInterleave or AlwaysInterleave attribute?

I don't mind changing the behavior of AlwaysInterleave to always interleave but as for MayInterleave I think it's better to leave it as now. IMHO, Orleans should have both options supported.

The ability to have calls which may interleave but not with others is crucial for a lot of use-cases, perhaps the most prominent is a so called system calls, which is kind of a special call that may not interleave with anything else. We have code that relies on this feature.

Example (from our system): we have a Projection actor that receives events that need to be projected on Elasticsearch index. For efficiency we batch index operations using timer and TaskCompletionSource, so senders got an ack only after the successful flush. On the other side, this actor participates in the complex index migration protocol which requires exclusive index access. When we send SwitchOver message to Projection actor it waits in Orleans queue until its turn and then executes exclusively, no event messages are processed concurrently (they're just sitting in Orleans queue).

Anyway, If we could have both options supported (and without breaking backward compatibility) - it's absolutely fine. Perhaps, some kind of boolean on MayInterleave which is false by default (ie current behavior?

[jason-bragg]

Did you mean MayInterleave or AlwaysInterleave attribute?

This change is only for AlwaysInterleave. It has no effect on MayInterleave. This will not be strictly backwards compatible for the AlwaysInterleave behavior, as it will change the way calls with that attribution behave slightly.

[yevhen]

I have no problem with that change