Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Tue, 30 Oct 2001 11:00:07 -0700

Geoff,

> CAC: unexpected select fail: 851971=S_iosLib_INVALID_FILE_DESCRIPTOR.

This message occurs under EPICS R3.13 (and also probably on earlier 
releases). The cause is one thread's shutting down a TCP circuit
while another thread is watching the TCP circuit's file descriptor
with select(). There are no portable mechanism for waking up a thread 
waiting in select() other than to synthesize a message over a file 
descriptor or to close() one of the file descriptors that select()
is watching. I chose the latter, but this does result in error 
status being returned from select(). Since this error can in certain 
instances (not this one) indicate a software failure I chose not to
suppress it.

In my experience the above message occurs very rarely, and it is benign, 
but it could be selectively suppressed if it becomes sufficiently 
annoying.

In EPICS R3.14 this message will not occur because I have removed 
from the CA client library all calls to select() in favor of a 100% 
thread scheduled design. This appears to be a reasonable choice
given the ubiquitous support for threads in modern operating systems.

Jeff

> 
> I'm running a CA client on IOC A accessing records on a IOC B.  After 
> performing a ca_clear_channel on all the channels on IOC A connected to 
> the IOC B I receive this error:
> CAC: unexpected select fail: 851971=S_iosLib_INVALID_FILE_DESCRIPTOR.
>  From what I understand about CA it appears the fd on IOC A which 
> handles the connection to IOC B has been released prematurely.
> 
> I found the errors source in src/ca/bsd_depen.c but am uncertain as to 
> how the select bits are set.
> 
> Any insights?  Thanks
> 
> Geoff
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System