Does your computer have exactly 8 cores (or subcores or whatever is the
official name of that hardware feaure)?
What happens if you use 7 futures instead of 8?
What happens if you use 9 (or 100) futures instead of 8?
PS: I don't know the low level details of the implementation of the
futures, but my guess is that in your example there is a main thread(?) and
8 futures, so you are running 9 things in 8 cores, and there is a race
condition and if you are unlucky it can cause a the program to block.
On Sat, May 30, 2020 at 1:12 PM Dominik Pantůček <
> Hello Racketeers,
> it didn't take long before I hit another strange behavior when
> extensively using futures. The setup is relatively simple: I am
> processing a large fxvector/flvector and I am processing it on a
> line-by-line basis (the vectors themselves are width*height in nature).
> To avoid races I setup a (make-vector height #f) to serve as a vector of
> locks. Locking is simple:
> (let lloop ()
> (when (not (vector-cas! locks y #f #t))
> .. do something ...
> (vector-set! locks y #f)
> Of course, the code in question is in 8 futures on my CPU and they are
> scheduled in parallel pretty consistently.
> Most of the time it works fine, but sometimes it just hangs with
> multiple CPU cores being utilized at 100% (I assume they are in the
> busy-wait "lloop").
> The problem is I cannot isolate a minimal working example from that. The
> code in question is about 3000 LoC and the issue expresses itself only
> in about 1 in 30 times just after the program has started. The GUI
> thread is running and there are lots of flonum operations and lots of
> thrown away flonum results (meaning GC gets triggered quite often).
> Also I cannot trigger the same issue with unsafe-vector*-cas! - I'll
> look into the differences in the source.
> I see this with latest Racket 3m.
> Any suggestions how to approach finding the source of the problem are -
> as always - very welcome.
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
You received this message because you are subscribed to the Google Groups
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
To view this discussion on the web visit