[GHC] #5556: Support pin-changing on ByteArray#s

[GHC]

#5556: Support pin-changing on ByteArray#s
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              Reporter:  pumpkin     |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.2.1
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by rwbarton):

 Let me make sure I've got this right: pinned ByteArrays currently live on
 a totally different heap than unpinned ones, right? If you pin an unpinned
 ByteArray without copying it, now you have a hole in the middle of your GC
 area to allocate around. I suppose you could split the containing GC block
 into two? a reasonable thing to do if you don't expect many temporarily-
 pinned ByteArrays to exist at any given time.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5556#comment:11>
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