Re: Postgres 8.3.5 - ECPG and the use of descriptors and cursors in multi-threaded programs - Mailing list pgsql-general

From Leif Jensen
Subject Re: Postgres 8.3.5 - ECPG and the use of descriptors and cursors in multi-threaded programs
Date
Msg-id 9448937.5650.1306748160680.JavaMail.root@quick
Whole thread Raw
Responses Re: Postgres 8.3.5 - ECPG and the use of descriptors and cursors in multi-threaded programs
List pgsql-general
Hello Bosco,

   Thank you for your comment. Yes, it would be nice to get some more comments on the allocate/deallocate on a
connectionissue. 

   I have verified that in my case deallocating a prepared statement, it guesses the wrong connection and returns an
error.(The right one is doing auto-deallocation at disconnect time, though). 

   However, I just noticed that allocating a descriptor with the "AT <connection>" clause,
EXEC SQL AT :_thisDbConn ALLOCATE DESCRIPTOR :descname;
generates an ECPGallocate_desc() call without any connection name and that this can "screw up" the ECPGget_desc()
functionwhen guessing a connection. I could of course use: 
EXEC SQL SET CONNECTION <connection name>;
before the allocate, but that would need mutex's all over to make sure that other threads will not set the connection
too.

   Any idea why the ecpg pre-compiler doesn't use the named connection for the ALLOCATE DESCRIPTOR statement even
thoughit allows it ? 

   Please help,

 Leif


----- "Bosco Rama" <postgres@boscorama.com> wrote:

> Leif Jensen wrote:
> >
> > Is it really not possible to use 2 separate connection within 1
> thread
> > at the same time ? or is it an error in the ecpg library ?
>
> It should be entirely possible to run multiple connections in a
> single
> thread as long as you manage the 'AT connName' clauses properly.
>
> Though, IIRC, using an 'AT connName' clause on any sort of
> 'deallocate'
> statement generates an error in ecpg:
>
>   ecpg -o test.c test.pgc
>   test.pgc:35: ERROR: AT option not allowed in DEALLOCATE statement
>
> This happens when trying to deallocate a query or a prepared
> statement.
> I don't use descriptors but the error message indicates it's _any_
> sort
> of deallocate.
>
> So, it would appear that you can allocate on a connection but not
> deallocate from one.  :-(
>
> I'm wonder if Tom or Michael can shine some light on this one?
>
> Bosco.

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