Michael Eager writes: > Andrew Haley wrote: > > Ian Lance Taylor writes: > > > > > > All objects shared between threads need to protected by a mutex, or by > > > some other type of memory barrier. > > > > It's an interesting contention -- that in GNU/Linux userspace there > > are essentially no legitimate uses for volatile. Hmmmm... > > I think that is an over-generalization. > > There are uses for volatile in user code, but they are limited. > Volatile is needed in the code which implements a mutex. I think that falls into Ian's category of "magic". > Volatile is needed when accessing a machine register, or an OS > variable (e.g., system time, errno) so that the latest value is > fetched or set, rather than being optimized away. > > It can also be used to share data between threads, but it becomes > problematic if accesses are not atomic. It's reasonable to use a > shared volatile sig_atomic_t to communicate between threads, to say > "I'm done" or "Start processing". Is that really safe, though? There's nothing to stop the machine from reordering memory writes, even if the compiler doesn't. Andrew.
