Re: Sharing an ADO connection object between two processes ?

"Herby" <>
6 Oct 2006 01:42:45 -0700
Egbert Nierop (MVP for IIS) wrote:

"Herby" <> wrote in message

Egbert Nierop (MVP for IIS) wrote:

"Herby" <> wrote in message

Egbert Nierop (MVP for IIS) wrote:

"Herby" <> wrote in message

We have a client and server application that run on the same
We want both to participate in the same transaction.

To acheive this I understand they need to share the same connection

The server currently supports a COM interface, as the client passes
across copies of simple data types Strings and integers etc.

But now they want to pass across the client ADO connection object.
data-writes within the server should then use this connection object
for creating its recordsets etc.

On return to the client - the client may then decide to commit or
rollback via the same connection object.

I understand the server would have a proxy back to the actual
connection object residing in the client address space. Is this
to work?

No offense intended but this is impossible. A connection, is in fact a
TCP/IP connection (for instance) to a SQL database server.

As you might guess, a single process can host one or more TCP/IP
connections, but one connection belongs _exactly_ to one

As soon as you 'share' the connection, you are fooling yourself to
that you have just one connection. You will have two connection in
there -will- be a lot of marshalling at the runtime of COM.
It's much more performance and security wise, to -not- share
objects. Just rely on the perfect resource pooling features of

Could you explain "Just rely on the perfect resource pooling features
of Windows?"

Create one or more COM objects that all use the same connection string.

Now open and close the connection (from the connection string) -per
within these COM objects.

Create (instanciate) those COM objects within a process.

Notice that even if you have called different methods from different COM
components that each opened and closed there respective ADODB.Connection
object, at the SQL server side you only see one connection being

You get that feature for free. This is called: "resource pooling". (and
used connection pooling).

With all respect to your managers, but they probably are thinking in
mainframe times or in times where the client-server connections were too
expensive so programmers in ancient times had to 'share' connections

My managers think they can just pass across an ADO connection object
from 1 process
to the other - I need to justify this is impossible?

This is impossible. You cannot share -one TCP-IP connection (or named
between 2 or more processes. You can 'share' a ADODB.connection object
this is fooling the managers. In effect, there will be 2 connections
your runtime has become sloppy and slower.

Thanks for your help.

Im sure you are all right. They still want me to produce a example
that proves it.
If there are two connections then they wont be part of the same
So there wont be no fooling?

Transactions must be dealt with through COM+. Don't they know that they are
trying to solve a problem that is solved already since NT4 (Transaction
Manager which is renamed to COM+ and Component Manager). THe DTC Districuted
Transaction Coordinator, allows you to share transactions among more servers
and connections.

Let them allow you to do the programming and thinking about 'how to' let
them do the business :)

To prove my point. Open SQL Server and query for active connections through
the SQL Enterprise Manager. Even if you share a connection among two
processes, there will be 2 connections (including the sloppyness, and
marshaling overhead).

I need to prove this.

My current problem is simply passing an ADO connection object within
the same process.
I need some help in doing this properly:
So my current server source has the following:

#import "C:\WINDOWS\ServicePackFiles\i386\msado15.dll" \
        rename("EOF", "EndOfFile")

typedef ADODB::_ConnectionPtr CnnPtr;

void TestClass::TestMethod(){

   CnnPtr conn;

   SetConnection( conn );


void TestClass::SetConnection(IUnknown* conn){

      HRESULT result = conn->QueryInterface(__uuidof( ADODB::Connection

          if( result == E_NOINTERFACE )
    return 0;

          if( result == S_OK )
    return 1;

         return 0;

I always get E_NOINTERFACE ?

Im just trying to simulate in-process the parameter passing and casting
to correct COM obnjects?

Please help - thanks.


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