Conference lassie::ucx

5231.0. "What conditions constitute an exception w select()" by CSC32::D_SANFORD () Sat Feb 15 1997 15:05

    UCX any version, DEC C V5.5, OpenVMS VAX V6.1

    The socket routine select() allows one to check sockets for pending
    exceptions.  What conditions constitute an exception to the select 
    routine?  A broken socket doesn't seem to be an exception and I 
    thought it would be.

    He sets socket options SO_REUSEADDR, SO_KEEPALIVE, and 
    UCX$C_TCP_PROBE_IDLE.  It's not that we don't detect broken sockets, 
    but that we detect them in the read handler.

    If you look at the select() function, it specifies and returns three 
    masks, one for reads, one for writes, and one for exceptions. When a 
    peer disconnects a socket (or when a connection times out, for that 
    matter), select sets a bit for the socket in the read mask. When I
    read from the socket, the read indicates an error and I handle it at 
    that point.

    The documentation for select() states:

	"On return, the longword exceptfds pointer contains a bit mask
	of the sockets that have exceptions pending."

    I have never seen a bit set in the exception mask. I would like to 
    know what constitutes an exception and under what conditions select() 
    sets a bit in the exception mask.

    Regards, Drew Sanford
    Customer Support Center
    RE: C970214-3869

execption is only set when there's oob data pending.