FreeTDS Development Group

[Alex Kiesel <alex.kiesel AT document-root.de>]

On Mon, 2004-01-19 at 11:47, ZIGLIO, Frediano, VF-IT wrote:

> > > If tds_process_cancel return success state is IDLE so
> > > ct_fetch/ct_results should just return CS_FAIL...
> > 
> > I added the check to ct_results/ct_fetch, that improves the situation.
> > However, it doesn't work reliable, though it worked in 80% of 
> > my tests.
> > 
> 
> This means you are able to reproduce it :) Good point. I never used sqsh, 
> do you just issue a query that returns a lot of data and then press ctrl-c 
> ??

Yes, this is it. You need a lot of data to be able to press Ctrl-C
before the results are all displayed.

Most of the time a 'select * from sysmessages' is enough to have
sufficient time for hitting the keys:)

> > This is a code snipplet from ct_results:
> >             /* Check for idle state */
> >             if (tds->state == TDS_IDLE)
> >                     return CS_FAIL;
> >                     
> 
> Perhaps test should be
> 
> if (tds->state != TDS_PENDING)
>       return CS_FAIL;

Ah, ok. I'll give that a try.

> > It comes down to goodread() which hangs - even I have checked the
> > tds-state before. It seems the ct_cancel can be invoked between the
> > non-idle check and the actual select.
> > 
> > Maybe goodread() needs to check the tds-state, too? 
> > 
> 
> No, it's a bad design here. goodread is a low level function and should not 
> use state (it's not expected to have knowledge of TDS state). You already 
> added code to check TDS_IDLE however or state get set in 
> tds_process_result_tokens or state is not TDS_IDLE (nor TDS_DEAD)... 
> I don't think sqsh be a multi-thread application... or perhaps it use 
> alarm() and issue cancel inside alarm signal ??

Sqsh is not a multithreaded application, but it indeed issues a cancel
within the signal handler. It does two thing from within this handler:
* send a cancel
* set a global variable which gets checked in all normal 'result
processing loops'. Those loops are left when this variable is set to
'1'. One excerpt:

/*
** cmd_do_sigint_cancel():
**
** Cancels current query upon receipt of SIGINT.
*/
static void cmd_do_sigint_cancel( sig, user_data )
        int sig ;
        void *user_data;
{
        if (user_data != NULL)
        {
                ct_cancel( (CS_CONNECTION*)user_data, (CS_COMMAND*)NULL,
CS_CANCEL_ATTN );
        }
        sg_canceled = True;
}

And from those loops:
        /*
        ** Suck in the results.
        */
        while ((retcode = ct_results( cmd, &result_type )) 
                == CS_SUCCEED)
        {
                /*
                ** Check to see if we were canceled.
                */
                if (sg_canceled == True)
                {
                        ct_cancel( conn, (CS_COMMAND*)NULL, CS_CANCEL_ALL );
                        ct_cmd_drop( cmd );
                        return(CMD_INTERRUPTED);
                }

[...]

-Alex