RE: Question on socket non block read

The call to sys_errno is also looks to be in the wrong place. It's being
called before any operation and then being checked after the recv.




Kevin Bucknum
Senior Programmer Analyst
MEDDATA/MEDTRON
Tel: 985-893-2550

-----Original Message-----
From: RPG400-L [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of
Bradley Stone
Sent: Thursday, September 17, 2015 2:04 PM
To: RPG programming on the IBM i (AS/400 and iSeries)
Subject: Re: Question on socket non block read

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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