Re: Bizarre interaction bug involving bash w/ lastpipe + Almquist 'wait'

[Harald van Dijk]

On 18/02/2020 16:46, Denys Vlasenko wrote:
> On Sat, Feb 8, 2020 at 7:41 PM Harald van Dijk <harald@gigawatt.nl> wrote:
> > If NetBSD sh
> > manages to avoid this pattern, and assuming NetBSD sh is not still
> > susceptible to one of those race conditions
>
> Please let us know what you discovered.

Okay, please take a look. I hope I managed to avoid race conditions in 
the test shell script.

test1.sh:

  i=1
  while test "$i" -lt 100000
  do
    printf "%d\r" "$i"
    "$@" test2.sh
    i=$((i + 1))
  done

test2.sh

  trap 'kill $!; exit 0' TERM
  { kill $$; exec sleep 1000; } &
  wait $!

To run:

  sh test1.sh $shell

For instance:

  sh test1.sh busybox ash

test1.sh will repeatedly run test2.sh and increment and print a counter 
variable to display progress.

test2.sh will immediately exit, in a complicated way, if all goes well. 
It may sleep for 1000s or fail to clean up its background process if 
something goes wrong.

On my system, I see:

  bash 5.0.11        - sleeps after a while
  bosh 2019-11-11    - sleeps after a while
  busybox 1.31.1 ash - ok
  dash 0.5.10.2      - ok
  dash (current)     - sleeps immediately
  fbsh 12.1          - ok *
  gwsh (current)     - leaves subprocesses
  ksh 93v            - sleeps after a while
  ksh 2020.0.0       - sleeps after a while
  mksh 57            - sleeps after a while
  nbsh (current)     - sleeps after a while *
  pdksh 5.2.14       - leaves subprocesses + sleeps after a while
  posh 0.13.1        - ok
  yash               - ok
  zsh                - sleeps after a while

* Because of the way I was running FreeBSD sh and NetBSD sh on qemu, I 
could not easily check what happens to the subprocesses.

I think that confirms that NetBSD sh does have a problem with a race 
condition, but that many shells have that same problem. It also tells me 
that there is another different problem in my shell that I should look at.

Cheers,
Harald van Dijk