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From: Markus Armbruster <armbru@redhat.com>
References: <20170720091902.22476-1-apahim@redhat.com>
	<20170720091902.22476-2-apahim@redhat.com>
Date: Thu, 20 Jul 2017 13:49:15 +0200
In-Reply-To: <20170720091902.22476-2-apahim@redhat.com> (Amador Pahim's
	message of "Thu, 20 Jul 2017 11:19:00 +0200")
Message-ID: <87inin1g78.fsf@dusky.pond.sub.org>
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Subject: Re: [Qemu-devel] [PATCH v3 1/3] qemu.py: fix is_running()
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To: Amador Pahim <apahim@redhat.com>
Cc: qemu-devel@nongnu.org, kwolf@redhat.com, ldoktor@redhat.com, ehabkost@redhat.com, mreitz@redhat.com, crosa@redhat.com, famz@redhat.com

Amador Pahim <apahim@redhat.com> writes:

> Current implementation is broken. It does not really test if the child
> process is running.

What usage exactly is broken by this?  Got a reproducer for me?

> The Popen.returncode will only be set after by a poll(), wait() or
> communicate(). If the Popen fails to launch a VM, the Popen.returncode
> will not turn to None by itself.

Hmm.  What is the value of .returncode then?

> Instead of using Popen.returncode, let's use Popen.poll(), which
> actually checks if child process has terminated.
>
> Signed-off-by: Amador Pahim <apahim@redhat.com>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> Reviewed-by: Fam Zheng <famz@redhat.com>
> ---
>  scripts/qemu.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/qemu.py b/scripts/qemu.py
> index 880e3e8219..f0fade32bd 100644
> --- a/scripts/qemu.py
> +++ b/scripts/qemu.py
> @@ -86,7 +86,7 @@ class QEMUMachine(object):
>              raise
>  
>      def is_running(self):
> -        return self._popen and (self._popen.returncode is None)
> +        return self._popen and (self._popen.poll() is None)
>  
>      def exitcode(self):
>          if self._popen is None:
               return None
           return self._popen.returncode

Why is this one safe?