Is it possible to have an out-of-process COM server where a separate O/S process is used for each object instance?

I have a legacy C++ "solution engine" that I have already wrapped as an in-process COM object for use by client applications that only require a single "solution engine".

However I now have a client application that requires multiple "solution engines". Unfortunately the underlying legacy code has enough global data, singletons and threading horrors that given available resources it isn't possible to have multiple开发者_开发百科 instances of it in-process simultaneously.

What I am hoping is that some kind soul can tell me of some COM magic where with the flip of a couple of registry settings it is possible to have a separate out-of-process COM server (separate operating system process) for each instance of the COM object requested.

Am I in luck?

Yes, this is possible. The key is to register your coclass by calling CoRegisterClassObject, and OR-in the value REGCLS_SINGLEUSE in the flags parameter.

If your project is an ATL 7.0+ project, you can do this by overriding CAtlExeModuleT::PreMessageLoop(), which is responsible for registering the class object, thusly:

HRESULT CATLHacksModule::PreMessageLoop(int nShow)
{
    HRESULT hr = RegisterClassObjects(CLSCTX_LOCAL_SERVER, REGCLS_SINGLEUSE);
    if (hr == S_OK)
    {
        if (m_bDelayShutdown && !StartMonitor())
        {
            hr = E_FAIL;
        }
    }
    else
    {
        m_bDelayShutdown = false;
    }
    return hr;
}

You would need a "master" coclass to lock in the EXE instance, similar to an "Application" interface. Locate the CoRegisterClassObject() call for its factory. And change the REGCLS argument to REGCLS_SINGLEUSE.

This will automatically unregister the class factory as soon as the first client connects to it. Calling CoCreateInstance() for that factory again starts a new instance of the server. I think.

I'm pretty sure this is not possible. A COM out-of-proc server has to globally register the class objects it provides (via CoRegisterClassObject); part of this registration is the class GUID. Obviously you cannot register the same GUID twice.