[GHC] #9923: Offer copy-on-GC sliced arrays

[GHC]

#9923: Offer copy-on-GC sliced arrays
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       Reporter:  dfeuer             |                   Owner:  simonmar
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Runtime System     |                 Version:  7.11
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 It's sometimes useful to split an array and send each part on to a
 different computation. Slicing works very well for this sort of thing, as
 long as both computations run to completion or become garbage at about the
 same time. It can work badly, however, if one computation is completed or
 abandoned and the other is retained—it may only hold a tiny slice, but
 that's enough to keep the entire array alive.

 The alternative, currently, is to copy the array to form two new arrays.
 This gets rid of the retention problem, but introduces a performance
 problem.

 One way to solve these problems might be to offer sliced arrays supported
 by the RTS. On collection, the garbage collector would copy each slice
 separately, turning it into an independent (and independently collectible)
 array.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9923>
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