Experimental Physics and
Industrial Control System

Torsten Bögershausen via Core-talk <core-talk at aps.anl.gov> · Thu, 6 Feb 2020 19:02:06 +0100

Hej again,
I think there is a risk for race conditions .
for me it seams as if bind() succeeded,
but then listen() fails.

From my (limited) understanding, 2 processes are allowed to bind() to

the same

port, for whatever reasons.

process 1 may use connect() on the port (specifying local port to be

something

defined.
   This is not usually used, but technically possible and allowed.)

process 2 may use listen() on the same port, listening for incomming

connections.

No both processes don’t interfere by using the same local port.

From that point of view, I would suspect that bind() can be done on the

same port

from 2 different processes without problems.

The “trouble” starts, when we want to listen() from 2 differnent

processes on

the same port,
that is not a valid use-case.

In this case, our EPICS code could handle this situation more gently,
by closing the bind() port, bind() to the next one and triy to listen.

Does this make any sense ?

/Torsten

On 06/02/20 13:44, Ralph Lange via Core-talk wrote:

Hej Torsten,

On Thu, 6 Feb 2020 at 13:35, Torsten Bögershausen

<torsten.bogershausen at ess.eu <mailto:torsten.bogershausen at ess.eu>> wrote:

          if ( listen ( IOC_sock, 20 ) < 0 ) {
              char sockErrBuf[64];
              epicsSocketConvertErrnoToString (
                  sockErrBuf, sizeof ( sockErrBuf ) );
              errlogPrintf ( "CAS: Listen error: %s\n",
                  sockErrBuf );
              epicsSocketDestroy (IOC_sock);
              epicsThreadSuspendSelf ();
          }

    We should be able to print out errno,
    to see what is going on and why listen fails.
    (could be EAGAIN ??) We need to find out...

Well, we have the error string, right? "Address already in use" is not

EAGAIN.

Also, the hanging IOC reports (casr 4) to be running on the 5064 port,

which matches the missing "dynamically assigned TCP port" warning -

sorry, I should have mentioned that in my original mail.

Cheers,
~Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System