#4514: System.Timeout cannot properly cancel IO actions with new IO manager
---------------------------------+------------------------------------------
Reporter: adept | Owner:
Type: bug | Status: new
Priority: normal | Component: Runtime System
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
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Consider the following simple "echo server":
{{{
module Main where
import Control.Concurrent
import Network
import System.IO
import System.Timeout
main :: IO ()
main = do
s <- listenOn (Service "7000")
loop s
return ()
loop :: Socket -> IO ThreadId
loop s = do
(hdr,_,_) <- accept s
hSetBuffering hdr LineBuffering
forkIO $ echo hdr
loop s
echo :: Handle -> IO ()
echo hdr = do
mstr <- timeout 5000000 $ hGetLine hdr
case mstr of
Just str -> do
hPutStrLn hdr str
hFlush hdr
echo hdr
Nothing -> do
putStrLn "Time out"
hClose hdr
return ()
}}}
When compiled without -threaded (GHC 7.0.1) it behaves as expected: you
could "telnet localhost 7000", send a couple of lines, see them echoed
back and if you don't type anything for 5 seconds, connection will be
closed. If you connect for the second (third, ...) time, behavior will be
the same.
Now, recompile the code with -threaded. On the first connect, everything
would be as expected. However, after the first time out, when you "telnet"
for the second time, behavior will be different.
1)Your lines would not be echoed back to you
2)Your connection would time out 5 seconds after you connected, no matter
if you type and send something or not
See [http://dl.dropbox.com/u/5748457/io-manager-cancel-fail.ogv this video
(OGV, 1.5mb)] for demonstration of behavior with -threaded.
GHC 6.12.3 behaves correctly with -threaded and without, so I guess that
new IO manager contributes to this situation.
This bug is confirmed to be present on Linux and MacOS X.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4514>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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