Use an IORef for QSemN
Replace the outer MVar in QSemN with an IORef. This should
probably be lighter, and it removes the need for uninterruptibleMask.
Previously Differential Revision https://phabricator.haskell.org/D4896
Replace the outer MVar in QSemN with an IORef. This should
probably be lighter, and it removes the need for uninterruptibleMask.
Previously Differential Revision https://phabricator.haskell.org/D4896