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Peter · Guest

How can I change the threading model of an already existing interface ?
I know it can't be done from the ATL tab of the project properties. The
option there seems pritty useless.

Some time ago I made an activeX dll with COM interface (without really
knowing much about COM).
I chose "single" as threading model when creating the COM object.

The person who needs to use the dll works under the .NET environment (vb).
rrrrr ... I have tried to debug small test apps using the dll but .net is
not for me ;-)

Following problem is something I have NOT been able to solve yet.
The dll class is instanciated in a new thread (in the .NET app) and once the
first function is called an exception occurs :
"An unhandled exception of type 'System.InvalidCastException' occurred in
*.exe"
"Additional information: QueryInterface for interface dll.class failed."

I have been searching the newsgroups and all I can find is references to the
app and com object not using the same threading model ?
(e.g.
[url]http://groups.google.be/groups?hl=nl&lr=&ie=UTF-8&threadm=78b36382.0210021252.52ba8a0%40posting.google.com&rnum=1&prev=/groups%3Fhl%3Dnl%26lr%3D%26ie%3DUTF-8%26q%3DI%27m%2Btrying%2Bto%2Bcreate%2Ba%2Bweb%2Bservice%2Bout%2Bof%2Ban%2Bexisting%2B(ATL%2BC%252B%252B)%2BCOM[/url] )

One other bit of information. In the ATL tab of the project properties I
use :
Instancing : "Single Use" and OLE init... "APARTMENTTHREADED"

So how can I resolve this issue ?

1. According to the link : "Register a proxy and stub for the interface. The
easiest way to do this
is to register the type library that defines the interface." like the MS
person suggests ?
I tried that and it doesn't seem to make a difference.
I have no clue what it does ? I ran it from the type library editor.
What is the difference with registering the active x server ?
The interface works when used in the main program thread without ever
registering the type library ??

2. Change the threading model of the interface ? To STA maybe ?
But how ?

3. I noticed that in .NET (from .NET help) the thread could possibly be set
to STA or MTA.
So suppose I can change the com interface to STA and make sure the person
who uses the dll creates such threads STA as well. Could that be the
solution ?

I'm out of ideas and I NEED to get this to work soon.
The code I put in the COM object (co)class is single threaded, hence me
chosing "single" when I created the COM object.
But I guess, because I use "Single use" in the Instancing property STA is
safe as well ??
Any other help is appreciated.

Jean-Marie Babet · Guest

Hello,

Peter · Guest

I'm not sure I understand your explanation ?
Btw. I use Borland c++ Builder 5

Do I have to change a #define somewhere ??

When I open the coclass files (h and cpp) for instance, where I added the
code,
I can see for instance :

class ATL_NO_VTABLE TCDDVDIOImpl :
public CComObjectRootEx<CComSingleThreadModel>,
public CComCoClass<TCDDVDIOImpl, &CLSID_CDDVDIO>,
public ICDDVDIO

So will "CComSingleThreadModel" this be replaced then or .. what ?

Peter · Guest

What do you mean with automation types ?

Jean-Marie Babet · Guest

Hello,

Jean-Marie Babet · Guest

Hello,

Automation types are types that are allowed as parameters in Automation
objects. For example, say I wanted to expose a method that takes a string; I
could make the parameter of type LPSTR or of type BSTR. LPSTR is not an
automation type while BSTR is. Likewise, if I wanted to expose an array
parameter, the Automation-type would be a SAFEARRAY whereas a plain array,
say char[] or char*, would not be an Automation type.

Basically, automation interfaces have a restricted list of types that they
can use. You can find more information at the following link:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/automat/htm/chap8_9a9a.asp

Regards,

Bruneau.

"Peter" <Peter (AT) Smart-Projects (DOT) net> wrote

Michael Harris · Guest

Peter. The ide will not do this for you.
To change and rebuild the entire dll. try this for an MTA free threaded
(actuall both). model.

(MTA) is what you need.

* REMOVE and obj. tds. csm files from the project dir.
* ATL options. check multiple use.
(allows multiple clients to call into one process).

* Change base class
as sugested. any class using
public CComObjectRootEx<CComSingleThreadModel>,
change to
public CComObjectRootEx<CComMultiThreadModel>,

* change threading model.
below find the line
DECLARE_THREADING_MODEL(otSingle);
change to
DECLARE_THREADING_MODEL(otBoth);

this will fix threading issues on your end.

# From the IDE menu. Projects / Edit option source.
find. '<SYSDEFINES'
somewhere in the line it will have
_ATL_SINGLE_THREADED
change to
_ATL_BOTH_THREADED

save all/ close all.
reopen and check the ATL options. make sure they appear correctly.
sometimes the edit option source thing takes a couple of attempts.
checking the radio button in ATL options will fail to change the option
source at times.

--
Michael

"Peter"

Peter · Guest

Thanks.
I'm not on my "developer PC" right now to try it but I have a question.

1. You say MTA, is this because you know this will solve the problem with
..NET ?
I mean, why MTA over STA for instance ?

2. You advice to change "Single Use" in the ATL to "Multiple Use"

I'm a bit scared of this. I'm not used to making threaded apps.
The dll is derived from a single thread application that I made !!
During debug mode (using "Single Use") I could see that each time I hit the
(.NET) test app button to create a new thread and make a new instance of the
COM object the constructor was called of the coclass and when the threads
were closed (app was closed) the destructor was called for each created
thread.
Using "Multi Use" I saw that each time the constructor was called but the
destructor was called only once ?
I'm not sure but it seemed each time a new instance was made but only one
instance was destroyed later on.
If it was the same instance all the time then calling then constructor again
doesn't seem a good idea ?? In my case variables are set-reset.

Given this information I'm also not sure if MTA is safe for me ? (Hence me
looking at STA)
What do you think ?

But if "Single Use", and each thread creates and uses it own instance of the
interface, inside the interface all is thread safe of course (?).
So that would be the solution then (?) right ?

"Michael Harris" <techonos-NO-SPAM- (AT) attbi (DOT) com> wrote

Michael Harris · Guest

Let me review a little.

< Some time ago I made an activeX dll with COM interface }

We are still talking about an ActiveX DLL. correct.?