> > the difference, and my main point is that the loop in ainc means > > that it is not a wait-free algorithm. this is not only sub optimal, > > but also could lead to incorrect behavior. > > I think a more likely possibility for the change is to have a > *copy* of what was incremented. lock incl 0(ax) won't tell you > what the value was when it was incremented.
you can read the code. that value is not used by the thread library. > But I don't see how the change will lead to an incorrect behavior. could. imagine you have two threads entering ainc. the loser will loop. imagine that before the loser completes his loop a third thread enters aintr and becomes a two-time loser. by induction it's possible that the loser never completes in n loops for any given n. this of course is basically the definition of a waiting algorithm. if your program depends on time-bounded behavior from the thread library, you could have trouble with a non-wait-free algorithm like this. perhaps my concern is unfounded. i'd like to hear the argument. - erik
