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

"Dilip" <>
12 Mar 2007 15:55:50 -0700
Howdy Gurus

I have a problem for which I am unable to come up with a decent

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_;

    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


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. I went in
this direction:

if (FAILED(hr))
    someLockClass lockObj(g_GlobalLock);

that, of course, wouldn't work.

Next, I tried going down the Double-checked locking pattern route and
that didn't work either.

if (FAILED(hr))
    // assume bTrouble is a static member var of COMWrapper
    bTrouble = true;
    someLockClass lockObj(g_GlobalLock);
    if (bTrouble)
    bTrouble = false;

The latter looks very fishy to me, in that I don't know if there is
some kind of race condition between the time I re-create the interface
pointer and set bTrouble to false and another worker thread coming
into CallCOMWrapperMethod(), failing and setting bTrouble to true

Any insights?

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