Re: DBI-Users> RE: DBD-Oracle - obtaining OCI handles from $dbh

On 27/10/2011 17:43, John Scoles wrote:
> Hmm....!!
>
> Well yes could be done but not as part of any release of DBD::Oracle it would have to be you own hacked version
>
Why is that John? What is the problem with  returning a C pointer via a 
DBD::Oracle attribute? It is just a pointer to some memory and loads of 
XS modules do this. There is an Oracle OCI module I played with for a 
short time but it is problematic to build. I looked at it as I could 
implement OCI calls separately from DBD::Oracle. I don't seem the harm 
in exposing OCI handles via DBD::Oracle - it would be useful for people 
like the OP.

> A few pointers to start.
>
> You will not be able to 'get' a handle and retrun it as a Scalar it will only ever be a pointer so you will just get some sort of number,
>
> You would simly edit the Oracle.xs file
>
> add in the   includes to your C++ .h files
>
> then add a few extra
>
> 'ora_'
>
> functions to take care of you C++ calls;
>
> A quick example
>
> void
> ora_some_c_call(dbh)
>     SV *dbh
>     PREINIT:
>     D_imp_dbh(dbh);  //this gets all the OCI handles for you (see dbdimp.h for the sturct imp_dbh_st)
>     CODE:
>     MYSomeC_Plus_Plus_method(dbh->envhp,dbh->svchp,dbh->seshp,dbh->srvhp);
>
>
He does not need to do this surely. So long as the C++ code and 
DBD::Oracle XS is running in the same process the pointers obtained from 
DBD::Oracle are just as valid in the C++ code as XS. However, if the 
code is multi-threaded there could be issues of multiple threads 
accessing the OCI handles at the same time.

>
> Myself I would write a small 'c' wrapper that would call you c++ and just a single .XS function that calls that small 'c' wrapper to fire your function.
>
My impression was that this was already done.
I quote:

"I have created some Perl bindings for some existing custom C++ libraries."

Martin
-- 

Martin J. Evans
Easysoft Limited
http://www.easysoft.com


> Hope this helps
>
> Cheers
> John
>
>
>> Date: Thu, 27 Oct 2011 09:48:54 -0400
>> From: [email protected]
>> To: [email protected]
>> CC: [email protected]
>> Subject: Re: DBI-Users>  RE: DBD-Oracle - obtaining OCI handles from $dbh
>>
>> Yes, I assumed I would need to extend DBD::Oracle is some manner
>> to allow those handles to be extracted from a $dbh object.
>>
>> The specific OCI handles that the C++ libraries use are
>>
>> - Environment handle
>> - Service Context handle
>> - Session handle
>> - Server handle
>>
>> My initial thought process on how it might work is this
>>
>> Create a method in the DBD::Oracle XS code to retrieve those
>> handles and return them back to Perl space as a scalar.
>>
>> Then with the Perl scalars that hold the OCI handles obtained from
>> $dbh, pass those values to my Perl bindings to the custom C++ libraries.
>> (I would need to extend the C++ libraries to allow the set methods
>> to the objects that hold those OCI handles).
>>
>> ...then the C++ libraries should work the same.
>>
>> The motivation for this approach is that I have a large code base
>> of these C++ libraries that have been tested, so it would cost
>> prohibitive to simply replace them with a pure Perl implementation.
>>
>> However, it is so much easier to work with Perl and DBI, it would
>> be useful to have DBI connect to the database and do some table
>> lookups. The C++ code could then be integrated seemlessly with my
>> Perl code. As time allows, I would gradually peel away functionality
>> from the legacy C++ libraries and implement it in Perl. But to
>> ease the migration path, this approach seemed to have some merits.
>>
>>
>> Quoting John Scoles ([email protected]):
>>>
>>>
>>>
>>>> Date: Wed, 26 Oct 2011 21:46:30 -0400
>>>> From: [email protected]
>>>> To: [email protected]
>>>> Subject: DBD-Oracle - obtaining OCI handles from $dbh
>>>>
>>>> I have created some Perl bindings for some existing custom C++
>>>> libraries.
>>>>
>>>> One of these C++ libraries implements a class that uses Oracle
>>>> OCI calls.
>>>>
>>>> I would like to create a connection to the Oracle database
>>>> using Perl's DBI (DBD::Oracle) module, and then ideally share
>>>> that connection with the C++ libraries.
>>>>
>>>> This would require me to extract the Oracle OCI handles from
>>>> the $dbh object...and then pass them to the C++ libraries.
>>>>
>>>> What would be the best way to get access to the underlying
>>>> Oracle OCI handles from a $dbh object?
>>> Hmm! Interesting concept. Which OCI handles are we talking about??
>>> Like Matin said you would have to do that with .XS and you would pass I guess a pointer to the
>>> 'C' struct that holds the pointers to DBD::Oraclles pointers?
>>>
>>> You would have to cast that struct into you C++ somehow??
>>>
>>> There would be a good number of handles to pass over. You might be able to find them by looking at the Perl process tree
>>> and finding the SV that holds the struct and then sening that over?
>>>
>>> All just guesses on my part.
>>>
>>> Interesting concept non the less.
>>>
>>> Cheers
>>> John
>>>
>