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From: Ken Brown <kbrown AT cornell DOT edu>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Re: Cygwin parenting issue
Date: Wed, 1 Jan 2020 23:24:47 +0000
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On 1/1/2020 4:01 PM, Norton Allen wrote:
> I have a project that involves starting a number of programs in the background 
> and then monitoring and reporting when they terminate. My approach has been to 
> write a small application called 'parent' that loops on waitpid() until there 
> are no more children. I invoke it in a script like:
> 
> #! /bin/bash
> program1 &
> program2 &
> program3 &
> exec parent
> 
> This of course works under Linux, but under Cygwin, although 'ps' documents the 
> parent/child relationship, waitpid() immediately returns ECHILD, indicating 
> there are no child processes. If I use the shell's waitpid, that works alright, 
> so I am wondering whether the problem is a casualty of the exec.
> 
> I have a minimal test setup at https://github.com/nthallen/test_parenting, along 
> with examples showing how it works under Linux and Cygwin.

This looks like the issue that was reported here:

   https://cygwin.com/ml/cygwin/2019-09/msg00263.html

It's been fixed.  Try updating the cygwin package.

$ uname -a
CYGWIN_NT-10.0 moufang2 3.1.2(0.340/5/3) 2019-12-29 17:28 x86_64 Cygwin

$ ./parent_test2.sh
Parent pid is 24159
Child pid is 24161
      UID     PID    PPID  TTY        STIME COMMAND
   kbrown   24159   24158 pty4     18:07:48 /usr/bin/bash
   kbrown   24162   24159 pty4     18:07:48 /usr/bin/ps
   kbrown   24161   24159 pty4     18:07:48 /usr/bin/sleep
Parent PID is 24159
      UID     PID    PPID  TTY        STIME COMMAND
   kbrown   24159   24158 pty4     18:07:48 /tmp/test_parenting/parent_test
   kbrown   24161   24159 pty4     18:07:48 /usr/bin/sleep
Process 24161 terminated: status 0000
No more children

Ken

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