python:没有外部命令的fork，并分别捕获stdout和stderr [英] python: fork without an external command, and capturing stdout and stderr separately

问题描述

我想在不运行外部命令的python中派生一个子进程...它将只运行定义的函数.我想分别捕获stdout和stderr.

I'd like to fork a subprocess in python that does not run an external command ... it would just run a defined function. And I want to capture stdout and stderr separately.

我知道如何使用os.fork()和os.pipe()，但是该机制只给了我两个fd.我正在寻找三个fd:一个用于stdin，一个用于stdout和一个用于stderr.在运行外部命令时，使用subprocess.Popen可以很容易地进行管理，但是该功能似乎不允许分叉本地功能.只是一个单独的可执行文件.

I know how to use os.fork() and os.pipe(), but that mechanism only gives me two fd's to work with. I'm looking for three fd's: one for stdin, one for stdout, and one for stderr. This is easy to manage using subprocess.Popen when running an external command, but that function doesn't seem to allow a local function to be forked; only a separate executable.

在ruby中，popen3命令可以将-"作为其命令参数，在这种情况下，发生分叉而没有调用任何外部命令，并且返回了我提到的3个fd.在python中是否有某种类似于该例程的python类似物?

In ruby, the popen3 command can take "-" as its command argument, and in this case, a fork takes place without any external command being invoked, and the 3 fd's I mentioned are returned. Is there some sort of python analog to this routine in python?

推荐答案

• 如果要从子进程中分别重定向stdout和stderr，则可以简单地为每个子进程创建两个单独的管道，而不是一个.我已经分享了相关代码.

  • If you want to redirect the stdout and stderr separately from the child process, you can simply create two separate pipes for each, instead of one. I have shared the relevant code.

    您还可以阅读此主题以获取有关此主题的更多知识:

    You can also read this thread to gain more knowledge on this subject: Redirect stdout to a file in Python?

    我提到了从子进程(Method1，Method2)写入stdout和stderr的两种方法

    I have mentioned two methods for writing to stdout, and stderr from the child process (Method1, Method2)

    如果还想写入子进程的stdin，则应创建另一个文件描述符.这次r将转到子进程，而w将转到父进程.

    If you want to write to stdin of child process as well, you should create another file descriptor. This time the r would go to child process, and the w would go to the parent process.

    import os
    import sys
    import time
    
    # Create two pipes. One for sys.stdout, and one for sys.stderr
    r_out, w_out = os.pipe()
    r_err, w_err = os.pipe()
    
    pid = os.fork()
    if pid == 0:
        # Child process
        os.close(r_out)
        os.close(r_err)
    
        w1 = os.fdopen(w_out, "w")
        w2 = os.fdopen(w_err, "w")
        sys.stdout = w1
        sys.stderr = w2
    
        # Note that flush=True is necessary only if you want to ensure the order of messages printed
        # across method1, and method2 is maintained
    
        # Method 1: Standard Python print messages
        print("Redirected to stdout #2", flush=True)
        print("Redirected to stderr #2", file=sys.stderr, flush=True)
    
        # Method 2: Using system file descriptors
        stdout_fd = sys.stdout.fileno()
        os.write(stdout_fd, b'Redirected to stdout')
    
        stderr_fd = sys.stderr.fileno()
        os.write(stderr_fd, b'Redirected to stderr')
    
        # Restore original stdout, and stderr
        sys.stdout = sys.__stdout__
        sys.stderr = sys.__stderr__
    
        # Close the file descriptors
        w1.close()
        w2.close()
    
    else:
        # Parent process
        os.close(w_out)
        os.close(w_err)
    
        r1 = os.fdopen(r_out)
        r2 = os.fdopen(r_err)
        for i in range(5):
            # Note that r1.read(), and r2.read() are non-blocking calls
            # You can run this while loop as long as you want.
            print("Read text (sysout):", r1.read())
            print("Read text (syserr):", r2.read())
            time.sleep(0.5)
    
    
    

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