Re: Question on socket non block read

[Bradley Stone <bvstone@xxxxxxxxx>]

select() should be called before the read()/recv() to know if the socket is
ready for the read (or write).

The timeout of 60 seconds seems quite big.  This isn't a delay if that's
what you're thinking.

If you specify 60 seconds that means it will wait on the select() for up to
60 seconds for "readiness" and then error if not.  If it's found to be
ready right away, it will pass through without error.

Here's how I do it...

do
  select()

  if (no error)
    read/write to socket
    if (error on read/write)
      exit
    endif
  else
    exit
  endif

enddo

Brad
www.bvstools.com

On Thu, Sep 17, 2015 at 12:42 PM, Jeff Young <jyoung0950@xxxxxxxxx> wrote:

> I have the following code:
>       // nbrecv(): Receive data on non-blocking socket w/timeout
>       //           using Select()
>       //    sock = (input) socket to receive data from
>       //     buf = (output) buffer to receive into (address of variable)
>       //    size = (input) size of buffer to send (size of variable)
>       //    secs = (input) seconds to wait before timing out
>       //
>       // Returns length received, or -1 upon failure (check errno!)
>       //+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>      P nbrecv          B                   export
>      D nbrecv          pi            10i 0
>      D    sock                       10i 0 value
>      D    buf                          *   value
>      D    size                       10i 0 value
>      D    secs                       10p 3 value
>
>      D readset         s                   like(fdset)
>      D timeout         ds                  likeds(timeval)
>      D err             s             10i 0 based(p_err)
>      D rc              s             10i 0
>
>       /free
>
>           p_err = sys_errno();
>
>           dow '1';
>
>               rc = recv(sock: buf: size: 0);
>               if (rc <> -1);
>                  return rc;
>               endif;
>               if (err <> EWOULDBLOCK);
>                  return rc;
>               endif;
>
>               // -----------------------------------
>               //  Wait until socket is readable
>               // -----------------------------------
>
>               FD_ZERO(readset);
>               FD_SET(sock: readset);
>               timeout.tv_sec = %int(secs);
>               timeout.tv_usec = (secs - timeout.tv_sec) * 1000000;
>
>               rc = select( sock+1             // descriptor count
>                          : %addr(readset)     // read set
>                          : *null              // write set
>                          : *null              // exception set
>                          : %addr(timeout) );  // timeout
>               select;
>               when rc = 0;
>                  err = ETIME;
>                  return -1;
>               when rc = -1;
>                  return -1;
>               endsl;
>
>           enddo;
>       /end-free
>      P                 E
>
> I am passing a value of 60 for the wait time.
> Is this routine correct?
> shouldn't the set of the wait time come first?
>
>
> Jeff Young
> Sr. Programmer Analyst
> --
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