[GHC] #8209: Race condition in setNumCapabilities

[GHC]

#8209: Race condition in setNumCapabilities
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        Reporter:  akio              |            Owner:  simonmar
            Type:  bug               |           Status:  new
        Priority:  highest           |        Milestone:  7.8.1
       Component:  Runtime System    |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  x86_64 (amd64)
 Type of failure:  Runtime crash     |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Simon Marlow <marlowsd@…>):

 In [changeset:aa779e092c4f4d6a6691f3a4fc4074e6359337f8/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="aa779e092c4f4d6a6691f3a4fc4074e6359337f8"
 Don't move Capabilities in setNumCapabilities (#8209)

 We have various problems with reallocating the array of Capabilities,
 due to threads in waitForReturnCapability that are already holding a
 pointer to a Capability.

 Rather than add more locking to make this safer, I decided it would be
 easier to ensure that we never move the Capabilities at all.  The
 capabilities array is now an array of pointers to Capabaility.  There
 are extra indirections, but it rarely matters - we don't often access
 Capabilities via the array, normally we already have a pointer to
 one.  I ran the parallel benchmarks and didn't see any difference.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8209#comment:9>
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