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Synchornization with Multiple processors

Posted on 1998-11-24
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Last Modified: 2013-11-20
Does anybody know about problems with using synchronization objects like CEvent, CSingleObject?
I am having strange problems on a Korean Win NT 4.0 with 4 processors.

Thanks,
Tommy
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Question by:tommyq
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Author Comment

by:tommyq
ID: 1325244
Edited text of question
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Expert Comment

by:Tommy Hui
ID: 1325245
What problems are you having?
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by:necfm
ID: 1325246
Tell us for which resource you are using the synchronisation object. Is your application is a multithreaded one? Can you give us the exact scenario?
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Author Comment

by:tommyq
ID: 1325247
Well, This is a multi theraded application. It uses synchronization objects like: CCriticalSection and mainly CEvent.
My question is regarding two points:
1. One of my customers is running the program on a 4 processor machine - does this make any change?
2. Is it right that if the second time the same thread locks on a critical section MFC will let him go thorugh (because it is the same thread)?

Thanks for your attention,
Tommy
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Accepted Solution

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necfm earned 400 total points
ID: 1325248
Hi Tommy,

Ans 1:
There will be no difference/problem with the Kernal objects even when they are run on a multi-processor kernal/machine.  But just note that in the Mutiprocessor case two threads can run at the same instance of time, compared to that of a Single processor case where though threads are said to run parallely there will be only one thread run at any instance of time (Because they are time sliced).

Ans 2:
Yes when the same thread is trying to lock on a critical section (WaitonSingleObject) again, the system will let it proceed.


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Author Comment

by:tommyq
ID: 1325249
necfm,

Is it possible that although my program was not written specifically for the a multi-processor machine, Win NT will take two of my threads who belong to the same process and run them in two different processors?

Thanks,
Tommy

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Expert Comment

by:necfm
ID: 1325250
Yes. That's how it works.  This is called asymetric multitasking.

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Author Comment

by:tommyq
ID: 1325251
So, overall, is ther any specail considearation to take when running an application on a multi-processor environment?
Or maybe if my app is thread safe on one processor it will be safe also on multi-processors?

Thanks,
Tommy
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Expert Comment

by:necfm
ID: 1325252
There is no special consideration in running multithreaded application on a multiprocessor environment.  Try to avoid run time libraries instead use win32 API for example instead of malloc use HeapAlloc with serialization.  If your application is thread safe on one processor it should probably work in multiprocessor environment.
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