[GHC] #10736: threadWaitRead/registerFd unusable

[GHC]

#10736: threadWaitRead/registerFd unusable
-------------------------------------+-------------------------------------
              Reporter:  mboes       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.2
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 The following program:
 {{{
 module Main where

 import System.Posix.IO
 import GHC.Event

 main = do
   Just mgr <- getSystemEventManager
   fd <- openFd "/tmp/bleh" ReadOnly Nothing defaultFileFlags { nonBlock =
 True }
   key <- registerFd mgr (\_ _ -> putStrLn "hello") fd evtRead MultiShot
   return ()
 }}}
 fails with:
 {{{
 *** Exception: modifyFdOnce: permission denied (Operation not permitted)
 }}}
 Since `threadWaitRead` and family are implemented in terms of
 `registerFd`, they also fail with the same error.

 Perhaps I am misunderstanding how to use this function, but in this case
 the conditions that must hold true regarding file descriptors should be
 documented somewhere.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10736>
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