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Message-ID: <49D4D802.8040005@pocock.com.au>
Date: Thu, 02 Apr 2009 16:21:38 +0100
From: Daniel Pocock <daniel AT pocock DOT com DOT au>
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To: cygwin AT cygwin DOT com
Subject: Re: execve issues, and execve with cygrunsrv
References: <49D0B0CD DOT 6050009 AT pocock DOT com DOT au> <20090331112427 DOT GC12738 AT calimero DOT vinschen DOT de>
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Corinna Vinschen wrote:
> On Mar 30 12:45, Daniel Pocock wrote:
>   
>> Hi,
>>
>> I'm using the execve call in a UNIX program (which works successfully),
>> and now I am testing it with Cygwin.
>>
>> The program is using execve as a way to restart itself after receiving
>> SIGHUP.
>>
>> The child process started by execve seems to be unable to work properly,
>> I observe various errors:
>> - DNS lookups fail
>> - binding to UDP sockets fails
>>     
>
> Is that with Cygwin 1.5.25 or with Cygwin 1.7?  If it's 1.5.25, could
> you try if this still occurs under Cygwin 1.7?
>   
I tried with both.

On 1.5.25, execve works, but the new process can't open sockets

On 1.7, the socket problem is gone, but there are other issues with 
cygrunsrv

> Does this only happen when started from a native Windows process (cmd.exe
> or so) or does this also happen when started from Cygwin's bash?
>
>   
Tested from Cygwin's bash, and as a service under cygrunsrv
>> Furthermore, I would like the process to become a service started by
>> cygrunsrv.  Is it safe to use execve in a process started by cygrunsrv?
>>     
>
> Did you try?
>   
I have now had a chance to try it under cygrunsrv from Cygwin 1.5.25 and 1.7

Under 1.5.25, it doesn't work because of the sockets issue

Under 1.7, a new issue is revealed: execve doesn't maintain the same 
process ID, so cygrunsrv thinks the service has actually stopped, and 
the cygrunsrv process exits.  This is obviously quite bad.

I tried to work around it by creating a PID file, and passing the -x 
parameter to cygrunsrv.  It seems that cygrunsrv only checks the PID 
file when first started, and not after execve.  A possible workaround 
would be for cygrunsrv to check for a new PID file each time the process 
exits.

This brings me to a few more questions:

- Can execve be implemented on Cygwin in such a way that the PID is 
preserved?  This would be the best solution for portability.

- Can cygrunsrv be enhanced to deal with this behaviour?



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