Thread nerver returns from WaitForSingleObject() !!!

Posted on 2000-03-22
Last Modified: 2013-12-03
I've a Mutex and 3 threads like below

HANDLE HMutex;  
bool   End = false;
void Thread_Running_1()
     WaitForSingleObejct( HMutex, INFINITE );
     // ..... do something important
  while( ! End );
void Thread_Running_2()
     WaitForSingleObejct( HMutex, INFINITE );
     // ..... do something important
  while( ! End );
//////   The main() function is only a case school
void main()
   // I create and lock the mutex

   HMutex = CreateMutex( ..... );
   WaitForSingleObejct( HMutex, INFINITE );

   // I create 2 threads and i start these threads

   CreateThread( ...., Thread_Running_1, ..... );
   CreateThread( ...., Thread_Running_2, ..... );

   // At this time, Thread 1 and 2 are in a wait state.
   // Now, We release and close the Mutex

   End = true;
   ReleaseMutex( HMutex );
   CloseHandle( HMutex );
   // At this time, the HMutex is REALLY DESTROYED

The trouble is when i release and close the Mutex handle,
only one thread will continue running. The other thread is
DEFINITELY lost. You can see the thread in "perfmon.exe".
You must call TerminateThread() api to shutdown the thread,
because the thread never returns from WaitForSingleObject().

When i close the Mutex handle, i do not know how many threads
are awaiting the mutex to be released. We could think that
the CloseHandle() will cease the WaitForSingleObject() execution
by returning WAIT_FAILED to threads but it DOES NOT.

This is same thing for Critical Section, Event, Semaphore.

How to prevent the thread from being lost ?
Question by:mars
  • 2
LVL 22

Accepted Solution

nietod earned 100 total points
ID: 2646034
First of all, you really shoudl be using critical sections for this, not mutexes.

next you need to declare end as volatile, otherwise it may be optimized out of existance, preventing the threads from ending.  (VERY likely.)

Finally  you should not close the mutex handle unil the other threads finish.  To do this you can wait on the thread handles with WaitForSingleObject().  The wait function will return when the thread ends.  So use this to wait until two the additional threads are done, then close the mutex handle

let me know if you have any quesitons.
LVL 22

Expert Comment

ID: 2646046
One more thing the threads that lock the mutex never release it.  You should have them release the mutex before then terminate.

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