y apply when
   nulling out, for the sake of garbage collection, a reference that is
   never accessed again.

   <li><code>weakCompareAndSet</code> atomically reads and conditionally
   writes a variable but does <em>not</em>
   create any happens-before orderings, so provides no guarantees
   with respect to previous or subsequent reads and writes of any
   variables other than the target of the <code>weakCompareAndSet</code>.

   <li> <code>compareAndSet</code>
   and all other read-and-update operations