To solve the exact structure-allocation limit problem noted in the
Quick Quiz on
page ,
we need a limit counter that can tell exactly when its limits are
exceeded.
One way of implementing such a limit counter is to
cause threads that have reserved counts to give them up.
One way to do this is to use atomic instructions.
Of course, atomic instructions will slow down the fastpath, but on the
other hand, it would be silly not to at least give them a try.