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freetds - Re: Cancel problem

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  • From: "Thompson, Bill D (London)" <ThompBil AT exchange.uk.ml.com>
  • To: "'TDS Development Group'" <freetds AT franklin.oit.unc.edu>
  • Subject: Re: Cancel problem
  • Date: Wed, 4 Sep 2002 17:53:01 +0100


Guys,

I don't profess to understand all of this thread, but would just like to
know if we have a working implementation of dbcancel() or not ?
:-)

Bill



> -----Original Message-----
> From: ZIGLIO Frediano [SMTP:Frediano.Ziglio AT vodafoneomnitel.it]
> Sent: Wednesday, September 04, 2002 5:00 PM
> To: TDS Development Group
> Subject: [freetds] Re: Cancel problem
>
> >
> > Ok, I was erroring on the side of safety. But if we can in
> > fact optimize
> > this by discarding whole packets then maybe we should. We
> > could do like:
> >
> > tds_read_packet() until header flag is 0x0f, then do normal processing
> > until done w/ cancel flag. It could still be all done inside
> > tds_process_cancel(), I think this is post 0.60 work. The patch as is
> > should be fairly non-distruptive.
> >
> Yes, I think so.
>
> Also note that you must not only test for 0xf but even for 0x3 (eom /
> acknowledge).
>
> Also I'd like to see another small modification... cancel stuff should
> work
> on multithread. We have always stated that tds should be thread safe
> (well,
> if thread safe is enabled) so only a thread should use a connection at a
> time.. well this should not be true for cancel. A cancel can be issued
> from
> another thread...
> Not so easy to handle, I know, but is a specification of dbcancel and
> SQLCancel (and I think even for ctlib is the same)... Thinking for
> solution
> a first problem that raise is: how can stop first thread (stopped in
> read)?
> Solution is quite easy: after send cancel server send some byte, so it
> unhold first thread... if this timeout closing socket unhold thread...
> other
> stuff are controlling critical section and events (quite complicated).
> This
> is another motivation of TDS_CANCELLING state...
>
> freddy77
>
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