[GSoC Project Proposal] ISO C11 threads.h implementation in GNU C Library

[Torvald Riegel]

On Fri, 2014-04-11 at 19:51 -0400, Rich Felker wrote:
> On Fri, Apr 11, 2014 at 11:57:06PM +0200, Torvald Riegel wrote:
> > > I may be mistaken, but I thought C11 mutex unlock had release
> > > semantics and lock had acquire semantics, rather than both being full
> > > barriers like they are in POSIX threads.
> > 
> > I agree.  However, in my not so humble opinion, this is a
> > (specification) defect in POSIX.  We currently don't implement mutexes
> > as full barriers (depends on the arch), and we shouldn't.
> 
> Then you should file a defect report with the Austin Group rather than
> silently implementing the interface in a nonconforming manner.

Sure, as soon as I get to this, this would be good.

What are you doing in your implementations BTW?

> > > Oh, completely. It would be unimaginably stupid to have separate
> > > implementations of threads. What I'm talking about is having separate
> > > implementations of synchronization primitives, which have absolutely
> > > no interdependency with the implementation of threads aside from
> > > accessing the thread id for recording mutex ownership and similar.
> > 
> > I agree that given how threads are currently implemented, mutex
> > implementations should be pretty isolated from each other and from the
> > specifics of the threads implementation.  However, should we ever want
> > to change how threads look internally, mutexes -- due to being blocking
> > constructs -- could have an effect on the threads implementations.
> 
> I think that's a vacuous "should we ever". The ridiculous thread
> implementation strategies that would require this were already tried
> and discredited. This is 2014 not 1998.

I suggest to have a look at recent ISO C++ proposals.  But given that
you seem to have a pretty strong opinion, I don't see the need to
discuss the details with you further.  If anyone else is interested, let
me know.