Re: [GHC] #13615: Nondeterminism in ‘pure’ function w/ parallel evaluation & memo combinators

[GHC]

#13615: Nondeterminism in ‘pure’ function w/ parallel evaluation & memo combinators
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        Reporter:  pacak             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 I have confirmed that eliminating the use of `parMap` in `solve`
 eliminates the issue as does replacing `rdeepseq` with `rseq`. I don't
 know whether the use of the `memo` combinator contributes as runtime blows
 up when it is removed

 Both uses of `A.unsafeUpdateM` in `unsafeInsertWith` (one in the
 `BitmapIndexed` branch and one in the `Full` branch) are problematic.
 Replacing either one with `A.update` decreases the failure rate, but the
 rate is still non-zero.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13615#comment:11>
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