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Date:	Tue, 18 Jun 2024 16:44:00 +0200
Message-ID:	<CAAvCNcBg4YQxGvPESnOtFuZFX7L=LQs8k4qJpOZXDqEDSeqWaQ@mail.gmail.com>
Subject:	Re: Cygwin outputting message to stderr on dofork EAGAIN failure even
	when Python exception is caught and handled
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
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From:	Dan Shelton via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Dan Shelton <dan DOT f DOT shelton AT gmail DOT com>
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On Mon, 17 Jun 2024 at 18:03, Dale Lobb (Sys Admin) via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
> Greetings, Nicholas;
>
> > From: Cygwin <cygwin-bounces+dale.lobb=bryanhealth DOT org AT cygwin DOT com> On Behalf Of Andrey Repin via Cygwin
> > Sent: Monday, June 17, 2024 2:58 AM
> > To: Nicholas Williams <nicholas DOT williams AT zaxiom DOT com>; cygwin AT cygwin DOT com
> > Cc: Andrey Repin <anrdaemon AT yandex DOT ru>
> > Subject: EXTERNAL SENDER: Re: Cygwin outputting message to stderr on dofork EAGAIN failure even when Python exception is caught and handled
> >
> > Greetings, Nicholas Williams! > We have a Python (installed and run through Cygwin) process running on > Windows Server 2022 that was very, very occasionally failing when subprocess. check_output was called: > 0 [main] python3 28481
> >
> > Greetings, Nicholas Williams!
> >
> > > We have a Python (installed and run through Cygwin) process running on
> > > Windows Server 2022 that was very, very occasionally failing when subprocess.check_output was called:
> >
> > > 0 [main] python3 28481 dofork: child -1 - forked process 16856 died
> > > unexpectedly, retry 0, exit code 0xC0000142, errno 11
> > > …
> > >     subprocess.check_output(["cygpath", "-w", directory.name], encoding="utf-8").strip()
> > > File "/usr/lib/python3.9/subprocess.py", line 424, in check_output <>
> > >      <>return run(*popenargs, stdout=PIPE, timeout=timeout, check=True, <>
> > > File "/usr/lib/python3.9/subprocess.py", line 505, in run <>
> > >      <>with Popen(*popenargs, **kwargs) as process: <>
> > > File "/usr/lib/python3.9/subprocess.py", line 951, in __init__ <>
> > >      <>self._execute_child(args, executable, preexec_fn, close_fds, <>
> > > File "/usr/lib/python3.9/subprocess.py", line 1754, in _execute_child
> > >     self.pid = _posixsubprocess.fork_exec(
> > > BlockingIOError: [Errno 11] Resource temporarily unavailable
> >
> > > Setting aside for a minute the various reasons this might be happening
> > > occasionally, which we cannot solve for at this moment, the error number
> > > (EAGAIN) indicates that you should “try again.” So that’s exactly what we
> > > did. We added a try/catch to the Python code to catch the BlockingIOError
> > > and, if and only if the error number is EAGAIN, we try up to two more times.
> > > This fixed the problem and caused the application to stop quitting. We
> > > output a warning to our log so that we don’t forget about the problem, but
> > > the warning only ever appears once, so retrying a single time seems to help.
> >
> > > However … even though Python handles the dofork error, turns it into a
> > > Python exception, and our code catches the Python exception and handles it
> > > properly, Cygwin (not Python … Cygwin) still outputs a message to stderr
> > > right before our warning message. This Cygwin error message shows up as an error in our log tracking:
> >
> > > 0 [main] python3 15042 dofork: child -1 - forked process 6780 died
> > > unexpectedly, retry 0, exit code 0xC0000142, errno 11
> > > 06/16 13:57:53. 87520: WARNING: Retrying command in 2 seconds due to EAGAIN: [the command we’re running]

Does python require fork(), or can it use posix_spawn() in this case?

Dan
-- 
Dan Shelton - Cluster Specialist Win/Lin/Bsd

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