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Communication from controller thread to worker thread

Posted on 1998-02-19
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Last Modified: 2010-04-10
I have created a SDI class in my Visual C++ Studio 5.0.  Under the View class, I have begun a worker thread called worker() by using AfxBeginThread().  Also, I have passed the pointer to the View class for the worker thread to pass the messages to controller thread.  However, if I would like to kill the worker thread at any time, I do not know how to pass a message or control to kill worker().  EndThread() can only be executed in worker(), not outside the worker().  Besides, the worker() is only a function, not a class object.  It does not have its own message handle.  Anyway, is there any method for me to kill worker() once user click CANCEL button on CView's menu?  Thanks.
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Question by:cw43
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mnguyen021997 earned 100 total points
ID: 1182548
TerminateThread with the following precautions :

TerminateThread is used to cause a thread to exit. When this occurs, the target thread has no chance to execute any user-mode code and its initial stack is not deallocated. DLLs attached to the thread are not notified that the thread is terminating.

TerminateThread is a dangerous function that should only be used in the most extreme cases. You should call TerminateThread only if you know exactly what the target thread is doing, and you control all of the code that the target thread could possibly be running at the time of the termination. For example, TerminateThread can result in the following problems:

•If the target thread owns a critical section, the critical section will not be released. •If the target thread is executing certain kernel32 calls when it is terminated, the kernel32 state for the thread's process could be inconsistent. •If the target thread is manipulating the global state of a shared DLL, the state of the DLL could be destroyed, affecting other users of the DLL.



A thread cannot protect itself against TerminateThread, other than by controlling access to its handles. The thread handle returned by the CreateThread and CreateProcess functions has THREAD_TERMINATE access, so any caller holding one of these handles can terminate your thread.

If the target thread is the last thread of a process when this function is called, the thread's process is also terminated.

The state of the thread object becomes signaled, releasing any other threads that had been waiting for the thread to terminate. The thread's termination status changes from STILL_ACTIVE to the value of the dwExitCode parameter.

Terminating a thread does not necessarily remove the thread object from the system. A thread object is deleted when the last thread handle is closed.
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by:nietod
ID: 1182549
Most likely, a better method is to use a semaphore of some sort to instruct the thread to terminate.  This allows the thread to terminate in a safe way.
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Author Comment

by:cw43
ID: 1182550
So, there is no way to communicate from controlling thread to worker thread?  In other words, if there are devices that I would like to release before I kill the worker thread, I have no way to control them, right?
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by:mnguyen021997
ID: 1182551
it really depends on how immediate this kill needs to occur, also how your thread function is structured?  if your worker thread is in an infinite loop doing work it may be best just to have it check a flag at some point and time and terminate, so for instance:

threadfunc()
{
   for(;;)
   {
     if ( g_bDone )
       Exit();
     else
       DoSomeFunction();
     Sleep(100);
   }
}

where g_bDone can be set anywhere.  if you need critical section security then you can add it via any of the many blocking objects.  explain what your function does and we can better assist.  without a message loop you can't send/receive messages.
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