[GHC] #4167: Add numSparks# to return the number of elements in the current capability's spark queue

[GHC]

#4167: Add numSparks# to return the number of elements in the current capability's
spark queue
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    Reporter:  ekmett            |        Owner:              
        Type:  feature request   |       Status:  new         
    Priority:  normal            |    Milestone:              
   Component:  Compiler          |      Version:  6.12.3      
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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Comment(by simonpj):

 This `numSparks#` idea would allow us to implement the "split when hungry"
 idea of Rainey et al; see "Lazy tree splitting", ICFP 2010.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4167#comment:2>
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