Re: Problem killing a thread

From:
"Doug Harrison [MVP]" <dsh@mvps.org>
Newsgroups:
microsoft.public.vc.mfc
Date:
Fri, 21 Jul 2006 23:30:54 -0500
Message-ID:
<mk73c21q0ij8q7etcdg6h0dlvpf9k4cdib@4ax.com>
On 21 Jul 2006 14:06:32 -0700, "Jon" <TheFakeJon@gmail.com> wrote:

Hello,

I am creating a DLL that creates another thread and does its work.
When I load the library, it calls CreateThread which spawns another
thread. I am having a hard time terminating the thread. For some
reason, when it runs DLL_PROCESS_DETACH, and executes TerminateThread,
the thread does not terminate.


Well, TerminateThread should be avoided for the reasons given here:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/terminatethread.asp

On the plus side, it doesn't call DllMains with DLL_THREAD_DETACH, so it
shouldn't deadlock due to DllMain serialization, which would otherwise
occur if you were waiting on the thread to exit normally during
DLL_PROCESS_DETACH.

Would anyone know what I could be doing wrong?

It seems fairly simple. Thanks

I have the following code:

////////////////////////////////////////////////////////////////
long WINAPI Temp(long lParam) {
    int result;
    for(;;) {
           // my new thread
    }

    return 0;
}
BOOL APIENTRY DllMain( HANDLE hModule, DWORD ul_reason_for_call,
LPVOID lpReserved ) {

    HANDLE hThread = new HANDLE();

That's genuinely twisted. :) It works only because HANDLE is a typedef for
void*, and new of course returns a pointer. What you want is simply:

   HANDLE hThread = 0;

Then get rid of the delete below. For reference, here's a corrected version
of what you have above:

   HANDLE* p = new HANDLE();

This creates a new HANDLE and zero-initializes it because you wrote
HANDLE() with parens.

     DWORD dwID;

    switch( ul_reason_for_call )
    {
        case DLL_PROCESS_ATTACH:
            hThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)Temp, NULL,
0, &dwID);


This overwrites the pointer stored in hThread.

             break;

        case DLL_PROCESS_DETACH:
            TerminateThread(hThread, 0);
            CloseHandle(hThread);
            delete(hThread);

This delete is undefined if thread creation succeeded in
DLL_PROCESS_ATTACH, because you would then be deleting a non-null pointer
you didn't allocate. The solution to all this was given earlier.

             MessageBox(NULL, "Detaching Process", "Note", MB_OK);
            break;

        default:
            break;
    }

   return TRUE;
}


Doing those things inside DllMain is risky at best. For more on the DllMain
restrictions, see:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/dllmain.asp
http://www.microsoft.com/whdc/driver/kernel/DLL_bestprac.mspx

For an MFC problem in this area, see:

http://support.microsoft.com/?kbid=142243

I'm afraid the best approach is for your DLL to expose functions that let
the EXE coordinate thread creation and termination.

--
Doug Harrison
Visual C++ MVP

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