Re: Sharing a smart pointer between threads

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Mon, 21 Aug 2006 13:25:58 -0400

Message-ID:

<u46DfbUxGHA.5056@TK2MSFTNGP06.phx.gbl>

PaulH <paul.heil@gmail.com> wrote:

I have a COM object smart pointer I'd like to share between threads
(as in the code below). The object works great in the thread it was
created in, but I get an exception when I use it in the thread I'm
sending it to.

In general, you can't do that. The interface pointer has to be
marshalled before it can be used in a different apartment. The easiest
way to do this in ATL is probably with CComGITPtr:

MyLib::IInterfacePtr m_Obj;
CMyApp::OnTimer()
{
    CComGITPtr<MyLib::IInterface> gitPtr(m_Obj);
    DWORD cookie = gitPtr.Detach();
    m_dialog->PostMessage(MYWM_UPDATE, cookie);
}

CMyDlg::OnUpdateMsg(WPARAM wParam, LPARAM /*lParam*/)
{
    DWORD cookie = static_cast<DWORD>(wParam);
    CComGITPtr<MyLib::IInterface> gitPtr(cookie);

    MyLib::IInterfacePtr pObj;
    gitPtr.CopyTo(&pObj);

    pObj->DoSomething();
}

--
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