Re: Re-creating free threaded objects in the face of multiple threads

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Mon, 12 Mar 2007 19:16:41 -0400

Message-ID:

<O7hI$xPZHHA.4520@TK2MSFTNGP06.phx.gbl>

Dilip <rdilipk@lycos.com> wrote:

I have a class that encapsulates calls to a free-threaded COM object.
Many worker threads create instances of this class on-the-fly and make
method calls on the COM object. In short:

class COMWrapper
{
static IOne* pOne_;

public:
   void CreateIOne(); // always called by only one thread at start-up
   void CallCOMWrapperMethod()
   {
   HRESULT hr = pOne_->CallThisMethod();
       if (FAILED(hr))
       {
       // how do I recreate IOne here on just one thread and let all
other worker threads slide by?
       }
   }
};

If the call fails, I want to release pOne_ and create it again.

The problem is the worker threads -- all of them execute something
like:

COMWrapper().CallCOMWrapperMethod();

so they are all merrily banging away at pOne_->CallThisMethod().
**If** by any chance, the call fails for some reason, it will fail for
all worker threads. I am a little confused how to recreate IOne* in
failure scenario in the presence of all waiting threads.

Try something like this:

void CallCOMWrapperMethod()
{
    for (;;) {
        IOne* pCopy = pOne_;
        HRESULT hr = pCopy->CallThisMethod();
        if (SUCCEEDED(hr)) break;

        // We may need to recreate the object
        Lock();
        if (pCopy == pOne_) {
            ReleaseIOne();
            CreateIOne();
        } // otherwise, somebody else beat us to it.
        Unlock();
    }
}

--
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925