#14621: GHC 8.2 GCed too early -------------------------------------+------------------------------------- Reporter: kazu-yamamoto | Owner: (none) Type: bug | Status: upstream Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => upstream Old description:

The network package uses mkWeakVar so that unreachable Sockets can be GCed. See the master branch of https://github.com/haskell/network

{{{ mkSocket :: CInt -> Family -> SocketType -> ProtocolNumber -> SocketStatus -> IO Socket mkSocket fd fam sType pNum stat = do mStat <- newMVar stat withSocketsDo $ return () let sock = Socket fd fam sType pNum mStat ##if MIN_VERSION_base(4,6,0) _ <- mkWeakMVar mStat $ close sock ##endif return sock }}}

The following code cause "threadWait: invalid argument (Bad file descriptor)" in accept:

{{{ module Main where

import Control.Concurrent (forkIO) import Control.Monad (void, forever) import Network.Socket hiding (recv) import Network.Socket.ByteString (recv, sendAll)

main :: IO () main = do let localhost = "localhost" listenPort = "9876" connectPort = "6789" proxy localhost listenPort connectPort

proxy :: HostName -> ServiceName -> ServiceName -> IO () proxy localhost listenPort connectPort = do fromClient <- serverSocket localhost listenPort toServer <- clientSocket localhost connectPort void $ forkIO $ relay toServer fromClient relay fromClient toServer

relay :: Socket -> Socket -> IO () relay s1 s2 = forever $ do payload <- recv s1 4096 sendAll s2 payload

serverSocket :: HostName -> ServiceName -> IO Socket serverSocket host port = do let hints = defaultHints { addrFlags = [AI_PASSIVE] , addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) bind sock (addrAddress addr) listen sock 1 fst <$> accept sock

clientSocket :: HostName -> ServiceName -> IO Socket clientSocket host port = do let hints = defaultHints { addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) connect sock (addrAddress addr) return sock }}}

GC frees sock while accepting. This occurs with GHC 8.2 or higher.

New description: The network package uses mkWeakVar so that unreachable Sockets can be GCed. See the master branch of https://github.com/haskell/network {{{#!hs mkSocket :: CInt -> Family -> SocketType -> ProtocolNumber -> SocketStatus -> IO Socket mkSocket fd fam sType pNum stat = do mStat <- newMVar stat withSocketsDo $ return () let sock = Socket fd fam sType pNum mStat ##if MIN_VERSION_base(4,6,0) _ <- mkWeakMVar mStat $ close sock ##endif return sock }}} The following code cause "threadWait: invalid argument (Bad file descriptor)" in accept: {{{#!hs module Main where import Control.Concurrent (forkIO) import Control.Monad (void, forever) import Network.Socket hiding (recv) import Network.Socket.ByteString (recv, sendAll) main :: IO () main = do let localhost = "localhost" listenPort = "9876" connectPort = "6789" proxy localhost listenPort connectPort proxy :: HostName -> ServiceName -> ServiceName -> IO () proxy localhost listenPort connectPort = do fromClient <- serverSocket localhost listenPort toServer <- clientSocket localhost connectPort void $ forkIO $ relay toServer fromClient relay fromClient toServer relay :: Socket -> Socket -> IO () relay s1 s2 = forever $ do payload <- recv s1 4096 sendAll s2 payload serverSocket :: HostName -> ServiceName -> IO Socket serverSocket host port = do let hints = defaultHints { addrFlags = [AI_PASSIVE] , addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) bind sock (addrAddress addr) listen sock 1 fst <$> accept sock clientSocket :: HostName -> ServiceName -> IO Socket clientSocket host port = do let hints = defaultHints { addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) connect sock (addrAddress addr) return sock }}} GC frees sock while accepting. This occurs with GHC 8.2 or higher. -- Comment: This actually appears to be a bug in the `network` library which has been exposed by more aggressive optimization by GHC. Specifically, `accept` doesn't ensure that the `Socket`'s `status` field is kept alive while the `accept` system call is underway. Consequently the GC correctly concludes that it can be collected. I have opened [[https://github.com/haskell/network/issues/287|network #287]] to track this. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14621#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14621: GHC 8.2 GCed too early -------------------------------------+------------------------------------- Reporter: kazu-yamamoto | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by kazu-yamamoto): * status: upstream => closed * resolution: => invalid -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14621#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler