Hello Rumen,
On 2026-03-31 23:33, Rumen Mitov via users wrote:
During FOSDEM, one of the discussions touched on the components' handling of incoming RPC calls. Currently this is done in a synchronous manner because (if I remember correctly) it was simply easier to implement it that way as opposed to handling it asynchronously.
What would be some of the challenges in handling this asynchronously?
This was implemented in very early versions of Genode [1]. A few traces of these days still slumber in the (private-API) interface [2]. Those bits are needed on the original L4 kernels to implement asynchronous notification as a service in Genode's core.
[1] https://genode.org/documentation/release-notes/10.02#Out-of-order_RPC_replie... [2] https://github.com/genodelabs/genode/blob/master/repos/base/include/base/rpc...
However, the out-of-order handling of RPCs is a can of worms, which is nicely illustrated by [3].
[3] https://genode.org/documentation/release-notes/10.02#Challenges
Eventually, we realized that we had needed out-of-order RPCs merely to accommodate the notion of *blocking* RPC calls. E.g., the timer's msleep used to be implemented that way. Once we identified blocking RPCs as an anti-pattern, we changed the RPC interfaces to become non-blocking by combining synchronous (but non-blocking) RPC with asynchronous notifications [4]. SO for the timer, there is now way to set an alarm (RPC), a way to take a look at the current time (RPC), and a way to receive an alarm (asynchronous notification).
[4] https://genode.org/documentation/release-notes/13.02#Timer_interface_turned_...
You may also find [5] worth reading to get a feel for the evolution of Genode's current design.
[5] https://genode.org/documentation/release-notes/16.11#Asynchronous_parent-chi...
Today, you should no longer find any blocking RPC throughout Genode. Hence, we can nicely define the need for out-of-order RPCs away.
Some problems are best solved by not having them. ;-)
Should the motivation behind your question be unrelated to the problem of blocking RPCs, I'd very much appreciate to learn more about your ambition for stepping away from synchronous RPC.
Cheers Norman