HP OpenVMS Systems

sys$qio and timeouts? (TCP/IP, ASTs)

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The Question is:

 
September 22, 1999
 
I can get information about whether a socket would block on a receive call
when I use the socket interface provided with the DEC C RTL.  But, I need,
for various reasons crucial to my project, to implement my sockets at a
lower level as a UCX device.  The
refore, I will read from and write to my sockets using $qio calls.  But, I
can't allow blocking on reads.  Furthermore, I need a solution that works
with all OpenVMS versions from 6.2 on.  The one solution I have been able to
find to this problem is to us
e the $qio option ucx$c_msg_peek option along with the ucx$c_msg_nbio
option.  The problem with this solution is that it does a direct I/O when
you make the call.  Over time this starts eating up resources.  This is
unacceptable for our problem.  We have
found a partial solution to this problem if we were to restrict matters to
OpenVMS 7.x:  we can use the DEC C RTL ioctl call.  But, this doesn't work
on 6.2.  There is an example in the OpenVMS 6.2 examples of implementing the
Unix ioctl on OpenVMS, but t
his example does not, in fact, work with OpenVMS 6.2 (even though the
example was, as we said, found there).
    Also, is there a way to specify a time out on a $qio call for sockets?
How are send and recv in the DEC C RTL library implemented?
    We would really appreciate any suggestions on this!  Thank you!
 
 
--Russell Dale and Alex Volnov,
Information Builders, Inc.
 
 

The Answer is :

 
  Use AST completion, and -- when you cannot otherwise deal with a
  completion that occurs later than expected, directly implement a
  timeout via $setimr and $cancel.
 
  Applications that are AST-based often do not require timeouts on
  I/O calls, though the incidence of time-based events within the
  application are quite commonly programmed.
 

  

     

     
answer written or last revised on ( 23-SEP-1999 )
     
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