Didier Kryn <kryn@???> writes:
> Le 25/07/2016 01:29, Rainer Weikusat a écrit :
>> Sleeping on a contended mutex is implemented in this way. But that's
>> supposed to be an exceptional case.
>

>     This is why, while advertizing itself as a cool "don't care"
> feature, a mutex is problematic:

I don't know who's advertising that "don't care" use of shared variables
would be "cool" and who's being targetted by this advertising (and I
don't even want to know) but I don't share this opinion. This applies
equally to single-threaded and multi-threaded applications. A mutex is a
synchronisation primitive useful for implementing userspace inter-thread
communication facilities (this is a bit too general).

> the programmer should make sure contention is exceptional and there is
> no risk of dead-lock.

Mutexes (or any other kind of lock) should usually be uncontended if
performance is considered important. It's often not necessary that
threads hold more than one mutex at the same time. In case it is, care
must be taken to ensure that they always try to acquire all members of
the shared set of mutexes in the same order to avoid deadlocks.