Le 27/07/2016 17:54, Rainer Weikusat a écrit :
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Didier Kryn <k...@in2p3.fr> writes:
Le 26/07/2016 12:59, Rainer Weikusat a écrit :
Didier Kryn <k...@in2p3.fr> 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).
This bias of mine comes from the fact that, in high level
languages, mutexes are embedded inside dedicated objects, and the
application can assign values to these objects exactly as it would do
for any other object (without specific care).
This could refer to Java 'synchronized things'. But these provide some
kind of high-level synchronization object called 'a monitor' and
'mutexes' (mutual exclusion locks) are just a primitive necessary for
implementing one. And the "use just like the global variables you'd
otherwise use" seems to suggest a programming style you seem to consider
more universal than I do.
Assuming I filled in the blanks halfway correctly, that's still a
certain style of programming which is already not a terribly good idea
for a single-threaded application. Using it in a multi-threaded one
'multi-threads' the inherent problems. This would be an example how one
can utilize the potential of more 'modern' technical (shared memory
multi-processors aka 'multicore CPUs') to achieve the same effect
(create a total chaos) much faster :->.
[...]
Never have written a single line of Java. It takes me a strong
motivation to start learning another language.
Mutex-protected objects can be built in C++, and are part of the
Ada language. It is difficult to decide what Ada should do in this case;
I don't know if the issue has been discussed but this kind of object
looks to me like a difficult compromise.
Didier
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