[syslog-ng] OT: why does writes to /dev/log block?

[Balazs Scheidler]

On Wed, 2005-06-15 at 20:08 +1200, Jason Haar wrote:
> Balazs Scheidler wrote:
> 
> >Basically, this is how it was designed to work. The syslog() call in
> >libc uses a blocking call to send messages to syslogd, if the socket is
> >opened (e.g. syslogd is running) then there's no timeout involved.
> >
> >  
> >
> So am alarm around the call should stop an app from hanging forever 
> (i.e. set an alarm of 10 sec, call syslog and if it hasn't returned 
> after 10 secs, the alarm will kill that exec)? Is there any way I can 
> emulate this condition? I tried sending a STOP signal to syslog-ng - it 
> stopped outputting to the syslog file all right - but didn't cause any 
> apps to hang - so it's not quite what I'm after...
> 
> [I have an app I wrote that writes to syslog that I'm now concerned for 
> it's reliability now that I've experienced this]
> 
> Thanks! Now that I've installed syslog-ng - I'm *not* expecting to come 
> into work to see the same condition tomorrow ;-)

syslog-ng is not different in that regard from stock syslogd, if
syslog-ng stops, and /dev/log is unix-stream then the application is
going to block.

if /dev/log is unix-dgram then it will probably not (I have not tested
this myself), though in this case the log message will be dropped.

I don't know whether alarm() is a good choice, I prefer not to rely on
it too much as it might interfere with low-level libraries (libc might
retry sending the message if it receives an EINTR from send() that alarm
would cause)

-- 
Bazsi