Re: MFC threads and critical section

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 09 Aug 2007 11:05:31 -0500

Message-ID:

<deemb3lsmk7n8kqs79h12h10pq4952bukr@4ax.com>

On Thu, 09 Aug 2007 08:55:27 -0700, one-trick-pony
<worldofpain.aamir@gmail.com> wrote:

Thanks. I need to clarify something in regards to threads and COM.
An article in SDK states that COM can be intialized in an application
as many times as desired as long as it is matched with unintializing
call.

In a single threaded application, is following techinque valid?

void main ( void )
{
    func1();
    func2();
}
void func1( )
{
    CoInitialize(somearguments);
    /* Do something here */
    CoUninitialize();
}
void func2( )
{
    CoInitialize(somearguments);
    /* Do something here */
    CoUninitialize();
}

As you can see a single threaded application that intializes and
uninitialized COM multiple times. I thought this was illegal. This
is one of the methods. The other method is calling COM intialize and
unitialize routine only once as shown below.

void main ( void )
{
    CoInitialize(somearguments);
    func1();
    func2();
   CoUninitialize();
}

void func1( )
{
    /* Do something here */
}
void func2( )
{
    /* Do something here */
}

Latter method is valid because I was told it is accurate.
But SDK sample states COM can be intialized and unitialized as many
times as desired. Therefore, my conclusion is both methods are
correct.

They are. The calls also can nest. There's normally little reason to
uninitialize COM before a thread exits, so your second example illustrates
the preferred way to do it. It's also more efficient. A couple of things to
note about console applications:

1. Threads which don't run message loops but do initialize COM can hang the
system indefinitely due to the hidden COM windows they create not
responding to various message broadcasts. So you wouldn't want to
initialize COM and run a long job without servicing a message loop.

2. Use "int main()" instead of the above. :)

--
Doug Harrison
Visual C++ MVP