[GHC] #1994: Data.ByteStirng.Lazy.hGetContents doesn't unlock i-node

[GHC]

#1994: Data.ByteStirng.Lazy.hGetContents doesn't unlock i-node
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    Reporter:  guest              |       Owner:       
        Type:  bug                |      Status:  new  
    Priority:  normal             |   Milestone:       
   Component:  libraries (other)  |     Version:  6.8.2
    Severity:  normal             |    Keywords:       
  Difficulty:  Unknown            |    Testcase:       
Architecture:  x86                |          Os:  Linux
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 I found that Data.ByteStirng.Lazy.hGetContents doesn't unlock i-node even
 after retreiving whole contents. Because of this and the fact that file
 locking mechanism of GHC uses i-node, sometimes it causes a problem whose
 cause is hard to find.

 See this example assuming file 'a' already exists:
 {{{
 testB = forM [1..] $ \_ -> do
     r <- B.readFile "a" >>= \r -> return $! B.length r `seq` r
     B.writeFile "b" (B8.pack "abc")
     renameFile "b" "a"
 }}}
 When I run this test on GHCi, it shows this error:

 *Main> testB
 *** Exception: b: openBinaryFile: resource busy (file is locked)

 I presume that this error happened because:

  1. readFile locks the i-node of 'a' and continues to lock after reading
 whole contents
  1. writeFile writes contents to 'b'
  1. Maybe GC runs and closes the handle but doesn't unlock i-node
  1. renaming 'b' to 'a' causes free the i-node of 'a'
  1. readFile locks another i-node of 'a'
  1. writeFile reuses the first i-node of 'a' which is still locked

 It is very difficult to find that readFile causes a problem, because an
 error occures in writeFile.

 I'm not sure this is a problem of ByteString or GC, but this problem
 doesn't occur when I use System.IO.hGetContents because it closes the
 handle and unlocks the i-node after retrieving whole contents.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1994>
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