Re: any fairness in NTPL pthread mutexes?

[James Courtier-Dutton <James@superbug.co.uk>]

Christopher Friesen wrote:
> I'm using NPTL.
>
> If I have a pthread mutex currently owned by a task, and two other tasks 
> try to lock it, when the mutex is unlocked, are there any rules about 
> the order in which the waiting tasks get the mutex (ie priority, FIFO, 
> etc.)?
>
> Thanks,
>
> Chris
> -

There is no fairness at all. It's currently not designed to be fair 
either. The reasons for this I can't remember, but there was talk at the 
KS about it and I just remember the answer. I think it had something to 
do with "If we implement fairness, general locking performance will drop 
and we prefer performance over fairness."

The solution is to modify your program so as not to rely on fairness.

James

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