可以在Windows上杀死在Network.Socket.accept上等待的Haskell或Haskell OS线程吗？

Question

-- thread A
t <- forkIO $ do
   _ <- accept listener -- blocks

---

-- thread B
killThread t

---

适用于Linux(可能也适用于OS X和FreeBSD),但不适用于Windows(尝试使用+ RTS -N4 -RTS等).

• A在这种情况下终止线程的正确方法是什么？
• 有没有办法A在特殊模式下分叉线程,允许在它阻塞的点终止accept？
• 如果A分叉forkOS而不是forkIO？

只有在通过错误报告提醒时,我才注意到这种不正常的Windows行为.

Answer 1

有趣的问题!

你不能打断阻止外部调用,所以我有点惊讶你能够在Linux上中断线程.此外,forkOS没有帮助 - 只是让外国代码分配线程本地存储,但与阻止行为无关.但请记住,接受可以设置为非阻塞:

如果队列中没有挂起的连接,并且套接字未标记为非阻塞,则accept()会阻止调用方,直到存在连接.如果套接字标记为非阻塞且队列中没有挂起的连接,则accept()将失败,并显示错误EAGAIN或EWOULDBLOCK.

这是在Posix系统的网络库中完成的操作.然后这允许accept被中断.

有关Windows的有趣说明:

-- On Windows, our sockets are not put in non-blocking mode (non-blocking
-- is not supported for regular file descriptors on Windows, and it would
-- be a pain to support it only for sockets).  So there are two cases:
--
--  - the threaded RTS uses safe calls for socket operations to get
--    non-blocking I/O, just like the rest of the I/O library
--
--  - with the non-threaded RTS, only some operations on sockets will be
--    non-blocking.  Reads and writes go through the normal async I/O
--    system.  accept() uses asyncDoProc so is non-blocking.  A handful
--    of others (recvFrom, sendFd, recvFd) will block all threads - if this
--    is a problem, -threaded is the workaround.

现在,使用-threaded运行时在Windows上接受使用accept_safe(允许其他线程进行) - 但它不会将套接字置于非阻塞模式:

accept sock@(MkSocket s family stype protocol status) = do
 currentStatus <- readMVar status
 okay <- sIsAcceptable sock
 if not okay
   then
     ioError (userError ("accept: can't perform accept on socket (" ++ (show (family,stype,protocol)) ++") in status " ++
     show currentStatus))
   else do
     let sz = sizeOfSockAddrByFamily family
     allocaBytes sz $ \ sockaddr -> do

#if defined(mingw32_HOST_OS) && defined(__GLASGOW_HASKELL__)
     new_sock <-
    if threaded
       then with (fromIntegral sz) $ \ ptr_len ->
          throwErrnoIfMinus1Retry "Network.Socket.accept" $
            c_accept_safe s sockaddr ptr_len
       else do
            paramData <- c_newAcceptParams s (fromIntegral sz) sockaddr
            rc        <- asyncDoProc c_acceptDoProc paramData
            new_sock  <- c_acceptNewSock    paramData
            c_free paramData
            when (rc /= 0)
                 (ioError (errnoToIOError "Network.Socket.accept" (Errno (fromIntegral rc)) Nothing Nothing))
        return new_sock

自2005年以来network,在带有-threaded的Windows 上的软件包版本显式使用标记为的accept调用safe,允许其他线程进行,但不将套接字本身设置为非阻塞模式(因此调用线程阻塞).

要解决它,我看到两个选项:

• 找出如何在Windows上进行非阻塞接受调用,并修补网络库 - 看看snap或yesod在这里做什么,看看他们是否已经解决了.
• 使用某种监督线程来伪造epoll,监视阻塞的子线程的进度.