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mutex/criticalsections

Started by Pactuul Jun 15, 2002 at 12:22 AM 1 reply 950+ views

Original Post

Jun 15, 2002 at 12:22 AM

ok i've been redesigning my app from the ground using memory leak detection, exceptions, and threads. Everything works properly except threads. I've been testing the threads. I've got a thread class that begins() and ends() threads. i've tested it by making 3 threads and having it print to a file the mem address (to see which thread is printing what) and a static count variable that's in the function. Like so:

  
DWORD Thread::ThreadProc()
{
	static fstream file;
	static count = 0;
	count++;

	if (count == 1)
		file.open("test.txt",ios::out);

	while (d_bIsRunning)
	{
		this->Lock();
		count++;
		file << &(*this) << "   " << count << endl;
		this->Unlock();
	}

	return 0;
}

the text file shows that the 3 threads are being called almost at the same time, but I notice it misprints the count number or the memory address in correctly. By that it looks like it was in the middle of executing my file << statement and it switched threads. Well I decide to add mutexs (then I also tried criticalsections) so my thread class is derived from mutex (hence the "this->Lock/Unlock()" calls) And this doesn't seem to fix it either. I'd really like it to execute one pass through the while loop completely without messing up. Anybody have thoughts or suggestions? -Pac [edited by - Pactuul on June 15, 2002 1:23:15 AM]

felonius

Jun 15, 2002 at 1:46 AM

I am not sure if I udnerstand you application correctly but it seem odd to me that you let your thread class derive from mutex (CCriticalSection I suppose). That way you will have a seperate mutex for each of your threads and you will not lock anything (since each thread has its own lock).

Instead you should create a single global mutex and then lock that. Instead of deriving from CCriticalSection you could let Thread contain a static CCriticalSection and then call Lock()/Unlock() on that one instead.

  

// Thread definition


static CCriticalSection mutex;

...

// In Threadproc()


while (d_bIsRunning)	
{
  mutex.Lock();		
  count++;
  file << &(*this) << "   " << count << endl;
  mutex.Unlock();
}

Also, you should encapsulate any place in the app that changes count with a mutex lock/unlock or it wont help much.

Pactuul

Author

Pactuul

Jun 15, 2002 at 10:16 AM

thanks! That actually solved my problem.
I decided to not derive thread from mutex and I just created a single global instance.

Because when I removed the lock/unlock, it still gave the same problem in the text file.

So I guess each thread having a mutex and locking/unlocking it''s own was very counterproductive.

Thanks for the ideas!

-Pac

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