🚀 go-pugleaf

Keith Bennett (kbennett@cpcug.org) wrote:
: The following questions pertain to programming sockets using
: IBM's TCP/IP for OS/2 version 2.0 (UN 64092).  Our app is
: running under OS/2 2.1 (not 2.11) and we hope to eventually
: upgrade to Warp.

: We have found that when doing a blocking read (recv()) on a
: socket, the read will not return if the machine on the other end
: of the socket has been switched off or rebooted.  (Despite our
: warnings, our customers do it from time to time and we have
: decided to accommodate for that somehow in our software.)

: 1) Is this behavior correct according to the TCP/IP standard (or
:    convention if there isn't a standard)?

: 2) Is there a way to get the recv() to detect the shutdown and
:    return an error code?

: 3) Are there any other situations that would cause the recv() to
:    block incorrectly?  (When planning our defense against this
:    situation we would like to know all of the possible causes up
:    front.)

: 4) What would you recommend as the best way to detect the demise
:    of the other end?  We've been thinking of having a separate
:    thread pinging all remote hosts that have sockets connected, and
:    forcibly closing any sockets connected to a machine that has
:    died.  That gets elaborate though, as we'd have to keep track of
:    which sockets are connected to whom, etc.

:    A slightly different solution would still have a separate thread
:    checking the other machines, but instead of pinging have a
:    separate special purpose socket with periodic keepalive
:    messages.  It is our understanding that sockets are more
:    reliable than ping (tcp vs. udp) and that sending messages
:    across an open socket would require less overhead than ping.
:    (Is that correct?)


I seem to remember the toolkit letting you set the TCP keepalive timeout 
through the setsockopt function.  Also, I believe thtat in IAK there is 
something to set keepalive for the entire system.  This might help your 
problem.

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