[GHC] #12852: threadWaitReadSTM does not provide a way to unregister action.

[GHC]

#12852: threadWaitReadSTM does not provide a way to unregister action.
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        Reporter:  qnikst            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2729
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"f43025340d05d3c6085c41e441d278745f34a317/ghc"
 f4302534/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f43025340d05d3c6085c41e441d278745f34a317"
 Allow to unregister threadWaitReadSTM action.

 Allow to unregister threadWaitReadSTM/threadWaitWriteSTM on
 a non-threaded runtime. Previosly noop action was returned,
 as a result it was not possible to unregister action, unless
 data arrives to Fd or it's closed.

 Fixes #12852.

 Reviewers: simonmar, hvr, austin, bgamari, trofi

 Reviewed By: bgamari, trofi

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2729

 GHC Trac Issues: #12852
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12852#comment:3>
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