Re: COM message pump

From:

=?Utf-8?B?R2Vvcmdl?= <George@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 30 Mar 2008 03:35:00 -0700

Message-ID:

<9A77B10C-7A1C-4633-87E6-713AB0EB3953@microsoft.com>

Thanks Igor,

Print the thread ID (as returned by GetCurrentThreadId) at the beginning
of CallMeManyTimesFromDifferentThreads to convince yourself that all
calls indeed execute on the same thread. What you observe is reentrancy
in action (which was the point of exercise): while the method is waiting
for pDummy->SomeMethod() call to return, it can be called again
(reentered) on the same thread.

I have verified you are correct. I posted my code and revised code for
printing thread ID below for your to review and double-check.

The thread 1 and 2 from other apartment will call
CallMeManyTimesFromDifferentThreads of component CSTAReentrancy. One method
call to CallMeManyTimesFromDifferentThreads in my understanding is one
message into message queue of STA owning component CSTAReentrancy, and since
the message queue retrieval is synchronized, no method will be able to invoke
on component CSTAReentrancy until last one returns (in other words, no
message to the message queue will be retrieved until the current message will
be processed and returned by STA owning thread).

From the test, you are correct. But I do not know why?

while the method is waiting
for pDummy->SomeMethod() call to return, it can be called again
(reentered) on the same thread.

called again means retrieving another message from message queue, and in my
current limited knowledge, owning STA thread will not retrieve until the
whole method CallMeManyTimesFromDifferentThreads returns.

Another confusing point is, the dummy object instance is created by client
thread, which is not in the same STA which owns component CSTAReentrancy. I
am not sure whether this character impacts the result and re-entrance issue?

Any comments? Anything wrong with my above statements?

Attached execution result and revised code,

[Code]
STDMETHODIMP
CSTAReentrancy::CallMeManyTimesFromDifferentThreads(ISomeDummyObj *pDummy)
{
    DWORD dwWritten;
    char buf [128] = {0};
    DWORD threadID = ::GetCurrentThreadId();
    sprintf(buf, "Thread ID is, %d \n", threadID);
    WriteFile(m_hFile, buf, sizeof(buf), &dwWritten, NULL);
    pDummy->SomeMethod();
    WriteFile(m_hFile, "1\r\n", 3, &dwWritten, NULL);
    pDummy->SomeMethod();
    WriteFile(m_hFile, "2\r\n", 3, &dwWritten, NULL);
    return S_OK;
}

Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               Thread ID is, 3392

                               1
2
1
Thread ID is, 3392

                               1
2
2
Thread ID is, 3392

                               1
2
Thread ID is, 3392

                               1
2
Thread ID is, 3392

                               1
2

[/Code]

regards and have a good weekend,
George