exception safe alternatives to QSem, QSemN, and SampleVar - GHC libraries

 This is an alternative to the deprecated QSem, QSemN, and SampleVar in
 GHC base. Those base modules are not exception safe and can be broken
 by killThread.
 .
 This package provides a library for the Haskell programming language.
 See http://www.haskell.org/ for more information on Haskell.