Hi Rowan, Hmm, this feels to me like more of a use case for threads or signal handlers. Trying to limit processing time by limiting turn count seems precarious to me as the amount of time spent on any turn could vary wildly.
That said the change you propose seems not too bad and I'd accept it, I just worry it's the tip of the iceberg here. Like will you find out that some particular callbacks in the RPC system can be especially expensive, and need to be counted as multiple turns? I think that would be going to far. If by any chance your synchronous processing could be made safe to run in a signal handler (requires using lockless data structures), I think a timer signal could be a pretty neat solution here. -Kenton On Wed, Jun 22, 2022 at 2:17 PM Rowan Reeve <rowanre...@gmail.com> wrote: > Hi Kenton, > > Our company is attempting to use Cap'n Proto in a soft-realtime system > where we need tight control over the resolution of promises. Our problem is > that we have some existing synchronous processing which needs to run > frequently and timely (on the order of 100 microseconds) but our system > must also service incoming RPCs (which might access results of said > processing) without missing a single processing window. > > What we would like to be able to do roughly corresponds the below > pseudocode inside our server: > > loop forever: > if before synchronous processing window: > poll single event > else: > do synchronous processing > > *WaitScope::poll* almost fulfills our needs, but it causes all new events > since the last poll to be picked up and their corresponding promises to be > resolved, in this case to incoming requests, which can occasionally cause > us to miss our window. Our individual RPC functions are relatively > short-lived, but when receiving many in a short span of time, we encounter > this timing issue. > > I think what we're looking for is an overload to *WaitScope::poll* > limiting the turn count: > https://pastebin.com/T4eFM60F > > Your thoughts? Otherwise could this be something that might be accepted as > a small pull request? > > Useful details: > > - C++ 17 with official capnp/kj library > - Linux 5.x kernel (so UnixEventPort as async provider) > > > > Rowan Reeve > > -- > You received this message because you are subscribed to the Google Groups > "Cap'n Proto" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to capnproto+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/capnproto/17eba638-4bbe-49fe-a270-c5e40b40b967n%40googlegroups.com > <https://groups.google.com/d/msgid/capnproto/17eba638-4bbe-49fe-a270-c5e40b40b967n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Cap'n Proto" group. To unsubscribe from this group and stop receiving emails from it, send an email to capnproto+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/capnproto/CAJouXQnK9rdh7Zv2y0RWT70zhBJkc8WEZeESqRn_Qz1o%2B3RR-g%40mail.gmail.com.
