Jamie Lokier wrote:
> That's right. It's possible to use atomic_compare_and_exchange for
> unlock; it's correct. But you get that extra bit of spinning with SMP,
> so atomic_dec is better.
In fact I don't see why Ulrich did the unlock code like this:
if (atomic_dec(val) != 1 ) {
val = 0;
futex_wake(&val, 1);
};
My current implementation is
c = atomic_xchg(val, 0) {
if (c=2) { // we own the lock, so
// val can be either of 1 or 2
futex_wake(&val, 1);
};
It does work fine in my tests on a dual core.
What do you think ?
-Michael
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