[freetds] cancel and timeout

Thompson, Bill D (London) bill_d_thompson at ml.com
Fri Jan 21 04:42:57 EST 2005


James,

I recently tested the dbsetinterrupt() functionality and it behaves
exactly like Sybase dblibrary AFAICT.

Bill

-----Original Message-----
From: freetds-bounces at lists.ibiblio.org
[mailto:freetds-bounces at lists.ibiblio.org] On Behalf Of James K. Lowden
Sent: 21 January 2005 03:37
To: FreeTDS Development Group
Subject: Re: [freetds] cancel and timeout


On Thu, 20 Jan 2005 17:11:12 -0000, "Thompson, Bill D (London)"
<bill_d_thompson at ml.com> wrote:
> > Timeout
> > -------
> > Now if a timeout (now query_timeout) a query_timeout_func it's
called.
> I
> > removed chkintr and hndlintr (one function it's sufficient).
> > query_start_time it's use for global time counting. I don't know if
> > query timeout on dblib works as expected. Perhaps even SQLFetch or
> > similar need setting timeout.
> 
> I think there are two functions because this then mirrors the
dblibrary
> interrupt handlers.  

Thanks for tackling this, Freddy.  

I think Bill means:

	void dbsetinterrupt(dbproc, chkintr, hndlintr)

	DBPROCESS     *dbproc;
	int           (*chkintr)();
	int           (*hndlintr)();

http://sybooks.sybase.com/onlinebooks/group-cnarc/cng1000e/dblib/@Generi
c__BookTextView/34848;pt=34848;uf=0#X
 

Note the comment:

"DB-Library does non-blocking reads from the server. While waiting for a
read from the server, it will call the chkintr() function to see if an
interrupt is pending. If chkintr() returns TRUE and a handler has been
installed as the hndlintr() for dbsetinterrupt, hndlintr() will be
called."

That's not how dblib_query_timeout() is currently coded.  chkintr should
be called periodically from within src/tds/net.c::goodread() until
either:

1.  the server sends data, or
2.  the query_timeout expires.

goodread() calls hndlintr after the timeout.  It should call it while
counting down to the timeout.  How often?  The docs don't say.  They say
they (Sybase) do non-blocking I/O, implying a busy wait.  I think it
would
be OK to call select(2) with a timeout of, say, 100 ms (blocking), then
call hndlintr, then busyfunc, then deduct 100 ms from query_timeout, and
call select(2) again.  Something like:

	for (ti = selecttimeout; 
		retcode = select(tds->s + 1, &fds, NULL, NULL, ti);
		ti.tv_usec -= 100) 
	{
		if (retcode < 0) {
			/* error */
		}
		if (retcode > 0) {
			break; /* data ready: read */
		}
		assert(retcode == 0); /* partial timeout */
		if (ti.tv_usec < 0) {
			ti.tv_sec--;
			ti.tv_usec += 1000;
		}

		if (ti.tv_sec < 0) break; /* really timed out */

		if ((*tds->chkintr)())
			(*tds->hndlintr());
		if (tds->busyfunc)
			(*tds->busyfunc)();
	}
	
	len = READSOCKET(tds->s, buf + got, buflen);
		
	if (tds->idlefunc)
		(*tds->idlefunc)();
	

These may also be interesting:

dbsetidle:
http://sybooks.sybase.com/onlinebooks/group-cnarc/cng1000e/dblib/@Generi
c__BookTextView/34650;pt=3564

"idlefunc() will be automatically called whenever DB-Library has
finished
reading output from the server."

dbsetbusy:
http://sybooks.sybase.com/onlinebooks/group-cnarc/cng1000e/dblib/@Generi
c__BookTextView/34263;pt=34263;uf=0#X

"automatically called whenever DB-Library is reading or waiting to read
output from the server."

--jkl
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