python pty.fork - 它是如何工作的

Question

http://docs.python.org/library/pty.html说——

pty.fork()¶ Fork. Connect the child’s controlling terminal to a pseudo-terminal. Return value is (pid, fd). Note that the child gets pid 0, and the fd is invalid. The parent’s return value is the pid of the child, and fd is a file descriptor connected to the child’s controlling terminal (and also to the child’s standard input and output).

这是什么意思？每个进程都有 3 个 fd(stdin、stdout、stderr)。现在这会影响这些 fds 吗？子进程不会有任何这些 fds 吗？我很困惑。--完全。

Answer 1

我想我终于在 Python 中得到了 pty.fork 的最小示例 - 因为我发现很难找到类似的示例，所以我将它张贴在这里作为 @joni 的示例回答。它主要基于:

• pty - Python os.forkpty why can't I make it work - Stack Overflow
• Weird platform dependent error: Using pty.fork()
• CodeIdol - Thinking about Programming Python, 3rd Edition - Parallel System Tools - Pipes
• Python code coverage: Lib/test/test_pty.py
• [Patches] [ python-Patches-656590 ] /dev/ptmx support for ptys (cygwin) (“master_open() 和 slave_open 自 2.0 以来已被弃用”)

特别令人讨厌的是发现仍然引用过时的 master_open() 的文档； pty.fork 不会生成子进程的事实，除非文件描述符(由 fork 方法返回)被读取父进程! (请注意，在 os.fork 中没有这样的要求)此外，os.fork 似乎更具可移植性(阅读很少有评论指出 pty.fork 在某些平台上不起作用)。

无论如何，这里首先是一个充当可执行文件的脚本 (pyecho.py)(它只是从标准输入中读取行，然后将它们以大写写回):

#!/usr/bin/env python
# pyecho.py

import sys;

print "pyecho starting..."

while True:
  print sys.stdin.readline().upper()

... 然后，这是实际的脚本(它要求 pyecho.py 在同一目录中):

#!/usr/bin/env python

import sys
import os
import time
import pty

def my_pty_fork():

  # fork this script
  try:
    ( child_pid, fd ) = pty.fork()    # OK
    #~ child_pid, fd = os.forkpty()      # OK
  except OSError as e:
    print str(e)

  #~ print "%d - %d" % (fd, child_pid)
  # NOTE - unlike OS fork; in pty fork we MUST use the fd variable
  #   somewhere (i.e. in parent process; it does not exist for child)
  # ... actually, we must READ from fd in parent process...
  #   if we don't - child process will never be spawned!

  if child_pid == 0:
    print "In Child Process: PID# %s" % os.getpid()
    # note: fd for child is invalid (-1) for pty fork!
    #~ print "%d - %d" % (fd, child_pid)

    # the os.exec replaces the child process
    sys.stdout.flush()
    try:
      #Note: "the first of these arguments is passed to the new program as its own name"
      # so:: "python": actual executable; "ThePythonProgram": name of executable in process list (`ps axf`); "pyecho.py": first argument to executable..
      os.execlp("python","ThePythonProgram","pyecho.py")
    except:
      print "Cannot spawn execlp..."
  else:
    print "In Parent Process: PID# %s" % os.getpid()
    # MUST read from fd; else no spawn of child!
    print os.read(fd, 100) # in fact, this line prints out the "In Child Process..." sentence above!

    os.write(fd,"message one\n")
    print os.read(fd, 100)        # message one
    time.sleep(2)
    os.write(fd,"message two\n")
    print os.read(fd, 10000)      # pyecho starting...\n MESSAGE ONE
    time.sleep(2)
    print os.read(fd, 10000)      # message two \n MESSAGE TWO
    # uncomment to lock (can exit with Ctrl-C)
    #~ while True:
      #~ print os.read(fd, 10000)


if __name__ == "__main__":
    my_pty_fork()

好吧，希望这对某人有帮助，
干杯!