On Mon, 20 Sep 2004 14:25:46 +0300, Peter Dimov <pdimov@mmltd.net> wrote:
Matt Hurd wrote:
Peter Dimov <pdimov@mmltd.net> wrote:
Matt Hurd wrote: I'm interested in getting something like "needs_lock" below into the normal traits, perhaps as part of boost thread. It informs you whether of not an operation on such a contiguous block needs a lock to be atomic.
For example, on ia32 32 bit aligned ops are atomic, on ia64 it is 64 bit. doubles on ia32 need locking to be atomic, on ia64 they don't.
What do you mean by "atomic"? Do you expect the change to the value to be visible to other threads?
Just memory consistent / atomic. That is, if you write to memory or read from memory all the bits will be guaranteed to make it as an indivisible unit. It doesn't say anything about the timing of the visibility or ordering w.r.t. like memory transactions.
How would you use such a thing? :-)
My main current use is in a macro I use than generates getter and setters with and without locking for simplifying the construction concurrent aware classes. So if it boost::needs_lock<T> for the type of the attribute it will lock, otherwise it goes phew if I'm running on a Pentium 4 I probably just saved a couple of hundred cycles and doesn't lock. matt.