Thread behavior in 7.8.3

[Ben Gamari]

Michael Jones <mike at proclivis.com> writes:

> I have a general question about thread behavior in 7.8.3 vs 7.6.X
>
> I moved from 7.6 to 7.8 and my application behaves very differently. I
> have three threads, an application thread that plots data with
> wxhaskell or sends it over a network (depends on settings), a thread
> doing usb bulk writes, and a thread doing usb bulk reads. Data is
> moved around with TChan, and TVar is used for coordination.
>
Are you using Bas van Dijk's `usb` library by any chance? If so, you
should be aware of this [1] issue.

> When the application was compiled with 7.6, my stream of usb traffic
> was smooth. With 7.8, there are lots of delays where nothing seems to
> be running. These delays are up to 40ms, whereas with 7.6 delays were
> a 1ms or so.
>
> When I add -N2 or -N4, the 7.8 program runs fine. But on 7.6 it runs
> fine without with -N2/4.
>
> The program is compiled -O2 with profiling. The -N2/4 version uses
> more memory, but in both cases with 7.8 and with 7.6 there is no space
> leak.
>
Have you looked at the RTS's output when run with `+RTS -sstderr`?
Is productivity any different between the two tests?

> I tired to compile and use -ls so I could take a look with
> threadscope, but the application hangs and writes no data to the file.
> The CPU fans run wild like it is in an infinite loop.
>
Oh dear, this doesn't sound good at all. Have you tried getting a
backtrace out of gdb? Usually this isn't terribly useful but in this
case since the event log is involved it might be getting stuck in the RTS
which should give a useful backtrace. If not, perhaps strace will give
some clues as to what is happening (you'll probably want to hide
SIGVTALM to improve signal/noise)?

Cheers,

- Ben


[1] https://github.com/basvandijk/usb/issues/7
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