mkfifo buffer exhibiting unexpected behaviour

mkfifo buffer exhibiting unexpected behaviour

[Steven Hum]

Running this simple test using clock from sutils to produce a repeating one second interval input stream..

mkfifo fifo
clock -i 1 -sf "T> stream one" >fifo &
clock -i 1 -sf "D> stream two" >fifo &
cat fifo

on void musl only the second fifo input stream is displayed.
on void glibc, both input streams are displayed interleaved as expected.

Are fifo buffers handled differently under musl?

Regards,
Steven

Re: mkfifo buffer exhibiting unexpected behaviour

[Rich Felker]

On Wed, Jan 16, 2019 at 08:08:00PM -0500, Steven Hum wrote:
> Running this simple test using clock from sutils to produce a repeating one second interval input stream..
> 
> mkfifo fifo
> clock -i 1 -sf "T> stream one" >fifo &
> clock -i 1 -sf "D> stream two" >fifo &
> cat fifo
> 
> on void musl only the second fifo input stream is displayed.
> on void glibc, both input streams are displayed interleaved as expected.
> 
> Are fifo buffers handled differently under musl?

No, aside from possible stdio buffering it's entirely a kernel matter.
I looked up the sutils source and see it's flushing after each output,
and tried it on an Alpine-based box here (with musl) and could not
reproduce what you're seeing. Both outputs are visible and roughly
interleaved (although their order sometimes swaps with scheduling, of
course).

Rich

Re: mkfifo buffer exhibiting unexpected behaviour

[Szabolcs Nagy]

* Steven Hum <sdothum@gmail.com> [2019-01-16 20:08:00 -0500]:
> Running this simple test using clock from sutils to produce a repeating one second interval input stream..
> 
> mkfifo fifo
> clock -i 1 -sf "T> stream one" >fifo &
> clock -i 1 -sf "D> stream two" >fifo &
> cat fifo
> 
> on void musl only the second fifo input stream is displayed.

maybe it was a regular file then, add ls -l before between
and after the clock calls.

if it's always a pipe then run the entire script under strace -f
to see what the clocks are doing.

> on void glibc, both input streams are displayed interleaved as expected.