From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-09-20 07:25:37
Anthony Williams wrote:
> Yes, there's overhead in a semaphore wait, but it's not pointless ---
> it allows the OS to schedule the threads appropriately. If you have
> contention, both threads have to do the same thing, otherwise you've
> added an implicit bias.
Bias in favor of the currently running thread is good as it improves
performance.
> We could just do a spin-wait if we want
> really-fast locks and unlocks ---
Spin-wait can also be slower; it just burns CPU instead of giving it to a
thread that could have done something with it. The performance of the
individual thread may look like an improvement, but the total time for the
task can still increase.