[GHC] #6057: hGetBufNonBlocking blocks the underlying handle on Windows

[GHC]

#6057: hGetBufNonBlocking blocks the underlying handle on Windows
---------------------------------+------------------------------------------
    Reporter:  cetinsert         |       Owner:                             
        Type:  bug               |      Status:  new                        
    Priority:  normal            |   Milestone:                             
   Component:  libraries/base    |     Version:  7.0.4                      
    Keywords:                    |          Os:  Windows                    
Architecture:  Unknown/Multiple  |     Failure:  Incorrect result at runtime
  Difficulty:  Unknown           |    Testcase:                             
   Blockedby:                    |    Blocking:                             
     Related:                    |  
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Comment(by cetinsert):

 Although I do not have code, I have pinned the problem down to following
 steps:

  1. Create sockets
  2. Convert sockets to handles
  3. Set handles to no buffering
  4. Do handshake IO using operations on handles
  5.
 [https://github.com/corsis/splice/commit/5e73712b0c01e1ccad158635433fd04d28149306#commitcomment-1280935
 Set same handles to no buffering again on a different Haskell thread]
  6. Observe the order-dependent behavior mentioned in this report:
     {{{
         a >- b $ j    -- forks and does step 5 on a Haskell thread
         b >- a $ j    -- forks and does step 5 on a Haskell thread
     }}}
     differs from
     {{{
         b >- a $ j    -- forks and does step 5 on a Haskell thread
         a >- b $ j    -- forks and does step 5 on a Haskell thread
     }}}


 Eliminating step 5 makes the problem go away:

 {{{
   a >- b $ j
   b >- a $ j
 }}}

 equals

 {{{
   b >- a $ j
   a >- b $ j
 }}}

 in behaviour.

 How can this be explained? It seems to happen both on Windows and Linux.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6057#comment:3>
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