Re: [Valgrind-developers] Valgrind and OpenMP

[Julian S. <js...@ac...>]

> My opinion is that the extraction of information about locking
> primitives from binary executables is a really powerful technique and
> would be a very interesting addition to Valgrind. The big question
> here is whether this is possible. This is at least a challenging
> research topic.

Yes.  I agree.

> One issue that puzzles me is the following: it is possible to
> implement a semaphore using one mutex and one condition variable, and
> it is possible to implement a mutex using one semaphore. libpthread
> implements semaphores, mutexes and condition variables via futexes. So
> how is it possible by only analyzing futex calls and control flow
> whether the (library) programmer has implemented a mutex or a
> semaphore ?

Probably irrelevant, but .. would it maybe help to model mutexes,
semaphores, in terms of simple message passing between threads?

eg, an unlock causes a token to be placed in a mailbox associated
with the mutex.  A lock request causes the requesting thread to 
remove the token from the mailbox associated with the mutex.  If 
the mailbox is empty then the thread blocks.

Anyway, I wonder if all such primitives can be modelled like this
and/or whether that is helpful for this problem.  Maybe not.

J