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Re: MT and variables simple question [message #43224 is a reply to message #43223]

Tue, 10 June 2014 15:59

ManfredHerr is currently offline

ManfredHerr
Messages: 67
Registered: February 2013
Location: Germany

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My two cents:
Mutex locks are necessary only then when the "variable" is compound. For example the mentioned fifo. It must be guaranteed that the full fifo entry is written before a second thread can interrupt and read it. For simple variables like integers a.s.o. there is no need to protect because they are written and read in an "atomic" action. The writing thread cannot be interrupted during the write-operation.

In the case where only one thread writes the fifo and only one thread reads it this atomicy can be used by tricky programmers to get rid of the lock at all. They write the fifo entry completely before they increment the write index. So the reading thread will only become aware of the new entry when it is fully written. The same is with the reading thread. First the entry is read completely before the read index is incremented to allow for reuse.

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[Message index]

		MT and variables simple question By: koldo on Thu, 05 June 2014 10:29
		Re: MT and variables simple question By: Didier on Thu, 05 June 2014 22:32
		Re: MT and variables simple question By: koldo on Fri, 06 June 2014 14:23
		Re: MT and variables simple question By: Didier on Fri, 06 June 2014 15:48
		Re: MT and variables simple question By: koldo on Sun, 08 June 2014 17:01
		Re: MT and variables simple question By: Didier on Mon, 09 June 2014 20:36
		Re: MT and variables simple question By: koldo on Tue, 10 June 2014 08:46
		Re: MT and variables simple question By: ManfredHerr on Tue, 10 June 2014 15:59
		Re: MT and variables simple question By: mirek on Wed, 11 June 2014 08:16
		Re: MT and variables simple question By: Didier on Thu, 12 June 2014 21:06
		Re: MT and variables simple question By: ManfredHerr on Thu, 12 June 2014 21:44
		Re: MT and variables simple question By: mirek on Mon, 16 June 2014 17:45

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