从createProcess外部获得的句柄中读取 [英] Reading from a handle obtained outside createProcess

问题描述

我试图创建一个进程，并通过我在 createProcess 函数之外提供的句柄与它进行通信：

  stdOutH < -  openFile（logDir stdout.log）ReadWriteMode 
 hSetBuffering stdOutH LineBuffering 
（_，_，_ ，ph）<  -  createProcess 
（procsomeproc[]）{std_out = UseHandle stdOutH 
，std_err = UseHandle stdErrH 
} 
 line<  -  hGetLine stdOutH 
 putStrLn $Got++行
  

someproc 进程向标准输出吐出一行，我想从产生它的进程读取它。然而，如果我尝试这样做，我会得到以下错误：
$ b hGetLine：非法操作（句柄已关闭）

我不明白为什么在创建的进程正在运行时关闭句柄。如果我使用 CreatePipe 而不是 UseHandle ，这是有效的，问题是我只想读第一行。但是这样做需要继续读取管道，否则在someproc。

那么，有没有一种方法可以使用 system.process 来通过 stdOutH 在上面描述的方式？

解决方案

createProcess 的这种行为是记录在案：

请注意，通过
UseHandle构造函数为std_in，std_out或std_err提供的句柄将通过调用此函数来关闭。

文档建议使用 createProcess _ 函数。

I'm trying to create a process, and communicate with it via a handle that I provide outside the createProcess function:

stdOutH <- openFile (logDir </> "stdout.log") ReadWriteMode
hSetBuffering stdOutH LineBuffering
(_, _, _, ph) <- createProcess $
    (proc "someproc" []) { std_out = UseHandle stdOutH
                         , std_err = UseHandle stdErrH
                         }
line <- hGetLine stdOutH
putStrLn $ "Got " ++ line

The "someproc" process spits a line out to the standard output, and I want to read it from the process that spawned it. However if I try to do this I get the following error:

hGetLine: illegal operation (handle is closed)

What I don't understand is why the handle is closed while the created process is running. This works if I use CreatePipe instead of UseHandle, the problem is that I only want to read the first line. But doing this requires to keep on reading from the pipe, otherwise it gets full after a certain amount of output by "someproc".

So, is there a way to use system.process to communicate two processes via stdOutH in the way described above?

解决方案

This behavior of createProcess is documented:

Note that Handles provided for std_in, std_out, or std_err via the UseHandle constructor will be closed by calling this function.

Documentation suggests to use createProcess_ function instead.

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