Re: [GHC] #14503: Killing a thread will block if there is another process reading from a handle

27 Nov 2017

      #14503: Killing a thread will block if there is another process reading from a
handle
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        Reporter:  dnadales          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Here is an complete all-Haskell repro,
 {{{#!hs
 -- Server.hs
 import System.IO
 import Network
 import Control.Monad
 import Control.Concurrent

 main = withSocketsDo $ do
     sock <- listenOn $ PortNumber 9090
     (h, _, _) <- accept sock
     forever $ do
         threadDelay 100000
         putStrLn "Trying to read something"
         s <- hGetLine h
         putStrLn $ "Got "++s
 }}}
 {{{#!hs
 -- Client.hs
 import Network
 import System.IO
 import Control.Concurrent

 main = readWithinNSecs

 readWithinNSecs :: IO ()
 readWithinNSecs = withSocketsDo $ do
   h <- connectTo "localhost" (PortNumber 9090)
   hSetBuffering h NoBuffering
   readerTid <- forkIO $ reader h
   threadDelay $ 2 * 10^6
   putStrLn "Killing the reader"
   killThread readerTid
   putStrLn "Reader thread killed"
   where
     reader h = do
       line <- hGetLine h
       putStrLn $ "Got " ++ line
 }}}

 Expected output (as seen on Debian 9 with GHC 8.2.2),
 {{{
 $ ghc Server.hs
 $ ghc Client.hs
 $ ./Server & ./Client
 Trying to read something
 Killing the reader
 Reader thread killed
 Server: <socket: 4>: hGetLine: end of file
 }}}

 Observed output (on Windows 10 with 64-bit GHC 8.2.1),
 {{{
 $ ghc Server.hs
 $ ghc -threaded Client.hs
 $ ./Server & ./Client
 Killing the reader
 Reader thread killed
 Trying to read something
 server.exe: <socket: 372>: hGetLine: failed (Unknown error)
 }}}

 Seems like things are working as expected.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14503#comment:3>
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