Chase your STA reentrancy blues away. Use IMessageFilter (with its known limitations, of course). I wrote this helper class to save some of your time :-). Its not very generic and you may need to tweak it here and there.


template <class T, DWORD dwTimeOut = 5000>
class ATL_NO_VTABLE IMessageFilterImpl : public IMessageFilter
    IMessageFilterImpl()     {}
    ~IMessageFilterImpl()    { RevokeFilter(); }


    HRESULT RegisterFilter() { return ::CoRegisterMessageFilter(static_cast<IMessageFilter*>(this), NULL);}
    HRESULT RevokeFilter(){ return ::CoRegisterMessageFilter(NULL, NULL); }

public: //IMessageFilter
    STDMETHODIMP_(DWORD) HandleInComingCall(DWORD dwCallType,HTASK threadIDCaller,DWORD dwTickCount,LPINTERFACEINFO lpInterfaceInfo)
        //we CANNOT reject these calls
        if(dwCallType == CALLTYPE_ASYNC_CALLPENDING || dwCallType == CALLTYPE_ASYNC)
            return SERVERCALL_ISHANDLED;

        T* pT = static_cast<T*>(this);
        return pT->ProcessInComingCall(dwCallType,threadIDCaller,dwTickCount,lpInterfaceInfo);

    STDMETHODIMP_(DWORD) MessagePending(HTASK threadIDCallee,DWORD dwTickCount,DWORD                                              dwPendingType)

    STDMETHODIMP_(DWORD) RetryRejectedCall(HTASK threadIDCallee,DWORD dwTickCount,DWORD                                                  dwRejectType)
        if(dwRejectType == SERVERCALL_REJECTED) { return -1; }
        //we must've got SERVERCALL_RETRYLATER
        return dwTimeOut;


1. Add the IMessageFilterImpl<> to your STA object's base class list

class ATL_NO_VTABLE CFoo :
    public CComObjectRootEx<CComSingleThreadModel>,
    public IMessageFilterImpl<CFoo>, ...

2. Add the  COM_INTERFACE_ENTRY(IMessageFilter) to your COM_MAP

    COM_INTERFACE_ENTRY(IMessageFilter) ...

3. Call RegisterFilter()  in the FinalConstruct()

4. Implement the following  helper as a class method:

DWORD ProcessInComingCall(DWORD dwCallType,HTASK threadIDCaller,DWORD dwTickCount,LPINTERFACEINFO lpInterfaceInfo)
    //Do the right thing !

    return -1; //return suitable Values !


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All rights reserved. No warrenties extended. Use at your own risk.
Do send Comments/Bugs to me :-)