Experimental Physics and
Industrial Control System

<[email protected]> · Thu, 6 Feb 2014 16:18:21 +0000

Hi Andrew,

> 
> I do not see that buffering behaviour when running an IOC in a Cygwin
> OpenSSH session either.
>

Thanks for doing that - it prompted me to do a bit more investigating. On my Cygwin installation there are several ways to create a terminal - mintty, bash, and xterm. If I run a native windows compiled softIoc.exe in the bash terminal window, all works fine. If I run it in a mintty terminal window, I don't see any standard error output until I exit the IOC - then it all appears on screen.  A Cygwin xterm window behaves the same - no stderr until the IOC is exited. If I type "tty" in the respective Cygwin windows, I see that mintty and xterm are both pseudo terminals whereas bash is a console session - I believe procServ uses forkpty(). So I think it boils down to Windows treating a Cygwin pty as non-interactive and thus buffering both stdout and stderr - I don't know whether it is possible to convince Windows to treat a Cygwin pty as a real terminal session? As you mentioned, the C99 standard mandates stderr to always be unbuffered so Windows is certainly not conforming her!
 e      

Regards,

Freddie

> -----Original Message-----
> From: Andrew Johnson [mailto:[email protected]]
> Sent: 05 February 2014 19:13
> To: [email protected]
> Subject: Re: stdout/stderr buffering on Windows
> 
> Hi Freddie,
> 
> On 02/05/2014 11:59 AM, [email protected] wrote:
> > just posting a note on an issue we have come across in case it is
> > helpful to anybody else. We are using Cygwin procServ on Windows to
> > start IOCs (Windows 7 / EPICS BASE 3.14.12.2) and, although stdout
> > was appearing when we typed commands in the telnet window, stderr was
> > not. When the IOC exited, however, the stderr output appeared so it
> > seems that stderr was being buffered.
> 
> > A "google" on the subject returned some
> > references to this sort of behaviour when the Windows runtime does
> > not recognize the connection as a "terminal" - running the IOC
> > directly in a console windows certainly work OK
> 
> I do not see that buffering behaviour when running an IOC in a Cygwin
> OpenSSH session either.
> 
> The Linux manpage for setvbuf(3) says "The standard error stream stderr
> is always unbuffered by default" which is apparently required by both
> the C89 and C99 standards. I would be reluctant to add code to the IOC
> to turn buffering off when it should never be necessary to do that.
> 
> Might this be indicative of a bug in procServ, or would it make sense/be
> possible for procServ to fix the Windows bug (rather than having to
> change the programs running under it)?
> 
> - Andrew
> --
> Advertising may be described as the science of arresting the human
> intelligence long enough to get money from it. -- Stephen Leacock
-- 
Scanned by iCritical.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System