Thanks Andrew - Perhaps I have worded this badly.

I understand that all clients will get the same instance back (and that is
indeed what seems to be happening), the problem is that calls into this
object seem not to be synchronized and so I see the
CMyObjectWithAProblem::myOnlyMethod method being called by both clients and
the first call does not complete before the second one starts, so my object
gets initialised twice (which breaks it).

So I was wondering why the calls are being dealt with at the same time given
that the object is created by apartment initialised threads..

The 2 clients in this example are the service that was written in the same
VC6 project as the singleton object and another service.

Cheers.
_________
Alex Smith

-----Original Message-----
From: Andrew Bolstridge [mailto:Andrew.BolstridgeAIT.CO.UK]
Sent: 20 September 2001 13:39
To: DCOMDISCUSS.MICROSOFT.COM
Subject: Re: Out of process singleton

It sounds perfectly normal, though you make it sound as if you have 1 client
calling the object in one paragraph, but 2 in a later para.

A singleton object means you have 1 instance created. no matter how many
clients 'create' this object, they actually get back this single instance.

When more than 1 client calls methods on that, then the calls are
synchronised (ie only 1 client will ever call a method at any given time),
but this does not prevent additional clients from calling the object.

Andy.

-----Original Message-----
From: Alex Smith [mailto:asmithMATRA.CO.UK]
Sent: 20 September 2001 13:08
To: DCOMDISCUSS.MICROSOFT.COM
Subject: Out of process singleton

Hi,

I have a COM Service, when it starts up, it starts a thread that creates a
COM object implemented within the same VC6 project. The COM object has the
ATL macro:
DECLARE_CLASSFACTORY_SINGLETON(CMyObjectWithAProblem) to define it as a
singleton.

The thread that creates this object begins with:
CoInitializeEx(NULL, COINIT_APARTMENTTHREADED ), so the created object is
running in a single threaded apartment.

The thread calls into this object through it's only exposed method which
effectively does this:
HRESULT CMyObjectWithAProblem::myOnlyMethod()
{
   if (!m_bInitialised)
   {
      Initialise(); /* Which will set the member m_bInitialised to TRUE on
success and will prevent multiple initialise calls */
   }

   DoTheRealWork();
}

The above all runs just fine except...

I have another service that has the first service as a dependency. When it
starts, it calls CoInitialize(NULL); then creates the out of process object
running in the first service and also calls myOnlyMethod() on it. I would
expect this call to be queued by COM until the other call(s) to the object
have finished, however, I see the calls being somewhat interwoven and
initialisation happens twice on the object in the first service. Anyone
have an explanation?

Further Info:
I have traced out the calls to myOnlyMethod() and, as I say, they are
interwoven. The trace I put in also showed that these calls were to the
object running in the same processID and threadID and the "this" pointer was
the same for both calls.

To try to get round this behaviour, that I see as incorrect, I tried using
CriticalSections (that didn't work as the calls were executed in the same
thread which can lock the same CriticalSection any number of times) and I
tried using Windows Events with AtlWaitWithMessageLoop to control entry.
This lead to deadlocks for some reason and now I'm stumped.

Thanks for any help you can give.
_________
Alex Smith

Project Manager
MATRA Systems (UK) Ltd <http://www.matra.co.uk>
Registered in Cardiff 2642797
Tel:+44 (0)2380 684 700 / Fax:+44 (0)2380 619 828
The content of this email is subject to MATRA's standard company disclaimers
which can be found at: http://www.matra.co.uk/EmailDisclaimer.html

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