如何在Haskell中检索进程的输出而不阻塞线程
在不阻塞的情况下，向stdin写入数据并从子进程的stdout读取数据的最佳方式是什么 子流程是通过如何在Haskell中检索进程的输出而不阻塞线程,haskell,Haskell,在不阻塞的情况下，向stdin写入数据并从子进程的stdout读取数据的最佳方式是什么 子流程是通过System.IO.createProcess创建的，它返回用于写入和读取子流程的句柄。书写和阅读是以文本形式完成的 例如，我进行非阻塞读取的最佳尝试是超时1$hGetLine out，如果不存在要读取的行，它将返回仅“某行”或Nothing。然而，这对我来说似乎是一种黑客行为，所以我正在寻找一种更“标准”的方式 谢谢以下是一些示例，说明如何以@jberryman提到的方式与衍生流程交互 程序与脚
System.IO.createProcess超时1$hGetLine out仅“某行”Nothing谢谢以下是一些示例，说明如何以@jberryman提到的方式与衍生流程交互 程序与脚本
/computemainimport System.Environment
import System.Timeout (timeout)
import Control.Concurrent
import Control.Concurrent (forkIO, threadDelay, killThread)
import Control.Concurrent.MVar (newEmptyMVar, putMVar, takeMVar)
import System.Process
import System.IO
-- blocking IO
main1 cmd tmicros = do
r <- createProcess (proc "./compute" []) { std_out = CreatePipe, std_in = CreatePipe }
let (Just inp, Just outp, _, phandle) = r
hSetBuffering inp NoBuffering
hPutStrLn inp cmd -- send a command
-- block until the response is received
contents <- hGetLine outp
putStrLn $ "got: " ++ contents
hClose inp -- and close the pipe
putStrLn "waiting for process to terminate"
waitForProcess phandle
-- non-blocking IO, send one line, wait the timeout period for a response
main2 cmd tmicros = do
r <- createProcess (proc "./compute" []) { std_out = CreatePipe, std_in = CreatePipe }
let (Just inp, Just outp, _, phandle) = r
hSetBuffering inp NoBuffering
hPutStrLn inp cmd -- send a command, will respond after 4 seconds
mvar <- newEmptyMVar
tid <- forkIO $ hGetLine outp >>= putMVar mvar
-- wait the timeout period for the response
result <- timeout tmicros (takeMVar mvar)
killThread tid
case result of
Nothing -> putStrLn "timed out"
Just x -> putStrLn $ "got: " ++ x
hClose inp -- and close the pipe
putStrLn "waiting for process to terminate"
waitForProcess phandle
-- non-block IO, send one line, report progress every timeout period
main3 cmd tmicros = do
r <- createProcess (proc "./compute" []) { std_out = CreatePipe, std_in = CreatePipe }
let (Just inp, Just outp, _, phandle) = r
hSetBuffering inp NoBuffering
hPutStrLn inp cmd -- send command
mvar <- newEmptyMVar
tid <- forkIO $ hGetLine outp >>= putMVar mvar
-- loop until response received; report progress every timeout period
let loop = do result <- timeout tmicros (takeMVar mvar)
case result of
Nothing -> putStrLn "still waiting..." >> loop
Just x -> return x
x <- loop
killThread tid
putStrLn $ "got: " ++ x
hClose inp -- and close the pipe
putStrLn "waiting for process to terminate"
waitForProcess phandle
{-
Usage: ./prog which delay timeout
where
which = main routine to run: 1, 2 or 3
delay = delay in seconds to send to compute script
timeout = timeout in seconds to wait for response
E.g.:
./prog 1 4 3 -- note: timeout is ignored for main1
./prog 2 2 3 -- should timeout
./prog 2 4 3 -- should get response
./prog 3 4 1 -- should see "still waiting..." a couple of times
-}
main = do
(which : vtime : tout : _) <- fmap (map read) getArgs
let cmd = "10 " ++ show vtime
tmicros = 1000000*tout :: Int
case which of
1 -> main1 cmd tmicros
2 -> main2 cmd tmicros
3 -> main3 cmd tmicros
_ -> error "huh?"
导入系统环境
导入系统。超时（超时）
导入控制。并发
导入控制。并发（forkIO、threadDelay、killThread）
import Control.Concurrent.MVar（newEmptyMVar、putMVar、takeMVar）
导入系统。进程
导入系统.IO
--阻塞IO
main1 cmd tmicros=do
r返回x
x main2 cmd tmicros
3->main3命令tmicros
_->错误“嗯？”
outhGetLineOnBlocking只是hGetLinehGetLinehReadytimeout 1$hGetLine…justNothinghGetLinehGetLinehClose outpterminateProcess phandlehClose inp