[GHC] #15193: QSem makes nonsense claim

[GHC]

#15193: QSem makes nonsense claim
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           Reporter:  dfeuer         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Core           |           Version:  8.2.2
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 It says waiting threads are serviced in FIFO order. This isn't really a
 meaningful statement. What does "first in" mean? Furthermore, the first
 step in `waitQSem` is `takeMVar`, which provides no ordering guarantees
 whatsoever. As far as I can tell, there's no meaningful difference between
 a thread waiting a long time in the queue and I've waiting a long time to
 get into the queue. So I think we probably want to weaken the promise here
 to match the `MVar` fairness guarantee: if a thread waits on a `TSem`, and
 that `TSem` continues to be signaled, then the thread will eventually
 proceed.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15193>
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