Re: My script makes a defunct subshell and sticks on read

[Øyvind Hvidsten]

On 30/01/18 22:51, Chet Ramey wrote:
> On 1/30/18 3:04 PM, Øyvind Hvidsten wrote:
>
> > Bash Version: 4.4
> > Patch Level: 12
> > Release Status: release
> >
> > Description:
> >      Running the included script, which does nothing useful but is cut down
> > a lot to demonstrate the issue, my main computer (amd64 based) counts to
> > several million, then Bash stops responding, using 100% cpu and ends up
> > with a defunct subshell. On my Raspberry Pi, running Raspbian Stretch and
> > the same version of Bash (4.4.12), the same thing happens after only a few
> > thousand iterations.
> >
> > Repeat-By:
> >      for ((i=0; ; i++)); do ((i%100)) || echo $i; exec {fd}<> >(:); read -t
> > 0.001 -u $fd; exec {fd}>&-; done
>
> In one sense, it's surprising that this works at all. You're opening a file
> descriptor read-write (and trying to read from it) to a pipe that's opened
> for writing only (the >(command) form is supposed to be used by processes
> that write to the resulting file).

Sorry for the spam. I just wanted to say it also happens without the 
subshell, when reading from a FIFO. In my first three tests, it stopped 
after 16500, 3100 and 125900 iterations, so it can (randomly) take a while.

----------------------
fifo=$(mktemp -u)
mkfifo "$fifo"
trap "rm $fifo" EXIT

echo "FIFO: $fifo"

exec {w}<> "$fifo"
for ((i=0; ; i++)); do
    (( i%100 )) || printf "%s\n" "$i"
    read -t 0.001 -u $w
done
----------------------