Strange CSingleLock crash in Multi-threaded OCX
Sam Gentile -- sgentile@gensym.com
Friday, December 20, 1996
Environment: MSVC 4.2b Windows NT 4.0
I am getting a strange crash in my OCX if I use in VB Design Mode or in a
Visual C++ program. I have an 32-bit OCX that has two threads. Basically,
there is one thread that runs every 100 milliseconds to do some work and
the other regular OCX thread. The code that crashes seems to run OK
hundreds of times I make the VB user program an EXE or run VC++ in
non-debug mode. But if I run VC++ in Debug or I put the control in any OLE
container in design mode, it crashes.
A stack dump shows:
The line where the problem starts:
CSingleLock csl(&m_critGsiInterface);
Where: CCriticalSection m_critGsiInterface is a member of the class.
The line in the constructor:
ASSERT(pObject->IsKindOf(RUNTIME_CLASS(CSyncObject)));
The debugger shows me that pObject is "CSyncObject". I don't get it.
CCriticalSection is certainly dervived from CSyncObject.
Then the line of the actual crash:
CRuntimeClass* pClassThis = GetRuntimeClass();
in CObject::IsKindOf()
What is going on here? Also, how do I stop a thread when someone exits the
program?
Thanks,
Sam Gentile
Mike Blaszczak -- mikeblas@nwlink.com
Saturday, December 21, 1996
At 11:58 12/20/96 -0500, Sam Gentile wrote:
>Environment: MSVC 4.2b Windows NT 4.0
>I am getting a strange crash in my OCX if I use in VB Design Mode or in a
>Visual C++ program. I have an 32-bit OCX that has two threads. Basically,
>there is one thread that runs every 100 milliseconds to do some work and
>the other regular OCX thread. The code that crashes seems to run OK
>hundreds of times I make the VB user program an EXE or run VC++ in
>non-debug mode. But if I run VC++ in Debug or I put the control in any OLE
>container in design mode, it crashes.
>A stack dump shows:
>The line where the problem starts:
> CSingleLock csl(&m_critGsiInterface);
>Where: CCriticalSection m_critGsiInterface is a member of the class.
>The line in the constructor:
> ASSERT(pObject->IsKindOf(RUNTIME_CLASS(CSyncObject)));
>The debugger shows me that pObject is "CSyncObject". I don't get it.
>CCriticalSection is certainly dervived from CSyncObject.
This is a symptom of not having your moudle state set correctly. What
you've described suggests that you have missed a AFX_MANAGE_STATE()
call somewhere that you need it.
>Also, how do I stop a thread when someone exits the program?
You might be tempted to post a message to it during your control's
ExitInstance(), but this is dangerous. In an OLE Control, ExitInstance()
is called from the control's DllMain() handler. If you terminate the
thread during this time, the thread's death will cause Windows to reenter
your DllMain() function and that means that you'll end up in a deadlock:
Windows won't let you enter the DllMain(), but your thread can't
terminate until it has successfully notified DllMain() of its death.
You'll probably be better off terminating your suboordinate thread in
an override of COleControl::OnClose(), which happens before the control's
OCX is unloaded but after the control is done being used.
You should post a message to your thread and wait on the thread handle
to make sure it really is dead. Don't, ever, under any circumstances ever,
call the TerminateThread() API.
.B ekiM
http://www.nwlink.com/~mikeblas/
I'm afraid I've become some sort of speed freak.
These words are my own. I do not speak on behalf of Microsoft.
TA -- siemens@inet.uni-c.dk
Monday, December 23, 1996
Sam Gentile wrote:
----------
> From: Sam Gentile
> To: mfc-l@netcom.com
> Subject: Strange CSingleLock crash in Multi-threaded OCX
> Date: 20. december 1996 17:58
>
> Environment: MSVC 4.2b Windows NT 4.0
>
> I am getting a strange crash in my OCX if I use in VB Design Mode or in a
> Visual C++ program. I have an 32-bit OCX that has two threads. Basically,
> there is one thread that runs every 100 milliseconds to do some work and
> the other regular OCX thread. The code that crashes seems to run OK
> hundreds of times I make the VB user program an EXE or run VC++ in
> non-debug mode. But if I run VC++ in Debug or I put the control in any
OLE
> container in design mode, it crashes.
>
> A stack dump shows:
>
> The line where the problem starts:
> CSingleLock csl(&m_critGsiInterface);
> Where: CCriticalSection m_critGsiInterface is a member of the class.
>
> The line in the constructor:
> ASSERT(pObject->IsKindOf(RUNTIME_CLASS(CSyncObject)));
> The debugger shows me that pObject is "CSyncObject". I don't get it.
> CCriticalSection is certainly dervived from CSyncObject.
>
> Then the line of the actual crash:
> CRuntimeClass* pClassThis = GetRuntimeClass();
>
> in CObject::IsKindOf()
>
> What is going on here? Also, how do I stop a thread when someone exits
the
> program?
>
> Thanks,
> Sam Gentile
>
>
In Mike Blaszczak's book 'MFC programming with Visual C++' on p. 479 he
states that:
"Even though CSingleLock can accept a pointer to a CCriticalSectionObject,
don't try it; it won't work. CCriticalSection uses a different access
pattern than the rest of the objects do. You will get an ASSERT message if
you try."
I've tried this and he's actually right, which means that the online books
contain an error as they tell you that it's possible to do so! This goes
for the CMultiLock as well.
If you need to access a CCriticalSection, just use the Lock() and Unlock()
members of it. If you need to use CMultiLock, for example, use a CMutex
instead of a CCriticalSection even though it's a lot heavier and slower.
Mike Thomas Jakobsen
Siemens@inet.uni-c.dk
Siemens A/S
Borupvang 3
DK-2750 Ballerup
+45 4477 4477
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