issue-491: Fix lost wakeups in spinlock
In uncontended cases, SpinLock::{Lock,Unlock} have an overhead of 13ns.
In cases where the lock is contended, SpinLock::Unlock has a bug where
it can fail to wakeup waiters, causing the overhead of
SpinLock::{Lock,Unlock} to blow up from 13ns to as high as 256ms. In
cases of heavy lock contention, this can cause applications to sleep
for minutes at a time without doing anything, appearing to hang.
The following fix slows down SpinLock::Unlock by 2ns in the uncontended
case, but speeds up SpinLock::Lock by up to almost 256ms in the
contended case where a wakeup ix mixed.
1 file changed
