SYSV message queues

[Chris Smith]

On Monday 12 Apr 2004 09:55, Vlad GALU wrote:

> > Did you try to grok what the msgrcv() call is supposed to return?
> > Specifically, read about -1/EAGAIN and IPC_NOWAIT. Then remove sleep().
>
> 	It is supposed to block, waiting for more events to be inserted
> into the queue.

Yes but sometimes it can't and will return an EAGAIN.
You *MUST* trap this and try the msgrcv again.

> >  > However, does anyone have a better design ?
> >
> > Yes. Use sockets.

Sockets (streams etc) work excellently _unless_ you periodically need to pick 
messages out of the queue out of FIFO order.  Priorities etc, or when you've 
got multiple processes reading a single queue and want to send a particular 
process a message. SYSV queues are just the ticket for this.....




Be carefull with SYSV Message Queues though as the default settings of queue 
size etc are broken in freeBSD/netBSD/openBSD (see my earlier email 
http://lists.FreeBSD.org/pipermail/freebsd-hackers/2004-March/006011.html )

Incidentally, what is the resolution of this??

Cheers, 
Chris
-- 
Chris Smith
  Technical Architect - netFluid Technology Ltd.
  "Internet Technologies, Distributed Systems and Tuxedo Consultancy"
  E: chris at nfluid.co.uk  W: http://www.nfluid.co.uk