Rdunlock happens before wrlock. Sent from my iPhone
On Dec 5, 2012, at 16:51, David Faure <[email protected]> wrote: > On Wednesday 05 December 2012 16:39:47 Leif Walsh wrote: >> The important synchronization point isn't the rdunlock, it's the wrlock. > > Well, you need two locks, for a happens-before relationship to be established. > If you remove the rdlock/rdunlock completely (since it could basically be a > no-op for a write operation anyway, as others pointed out earlier), then this > will be more clear: this write might never become visible to the other thread. > >> I have a hard time believing that you can take a pthread write lock and then >> look at a value some other processor wrote before you took the lock and not >> get that value. > > You say "before", but this assumes a global ordering, which you don't get, > when not using atomics or the proper locks. > Each CPU can have a different notion of "before", without the correct > synchronization primitives. > > I recommend reading "C++ Concurrency in action" by Anthony Williams, it > taught > me a lot on all this all works... definitely not a simple topic. > > -- > David Faure, [email protected], http://www.davidfaure.fr > Working on KDE, in particular KDE Frameworks 5 > ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Valgrind-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/valgrind-users
