[GHC] #3875: DPH QuickHull example crashes on SPARC with -N > 1

[GHC]

#3875: DPH QuickHull example crashes on SPARC with -N > 1
-------------------------------+--------------------------------------------
    Reporter:  benl            |        Owner:  benl         
        Type:  bug             |       Status:  assigned     
    Priority:  high            |    Milestone:  6.12.2       
   Component:  Runtime System  |      Version:  6.13         
    Keywords:                  |   Difficulty:               
          Os:  Solaris         |     Testcase:               
Architecture:  sparc           |      Failure:  Runtime crash
-------------------------------+--------------------------------------------

Comment(by benl):

 The `concprog002` testsuite program also crashes consistently with `-N16`
 and -`N32`.

 Once when running it when -N16 it said:
 {{{
 benl at greyarea:~/devel/ghc/ghc-head-devel/tmp$ ./Server +RTS -N16 >
 /dev/null
 Server: thread blocked indefinitely in an MVar operation
 Server: thread blocked indefinitely in an MVar operation
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3875#comment:5>
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