run command in child process without

local.py

# -*- coding: utf-8 -*-
import errno
import os
import fcntl

# !! License GPLv2 !!

# only work on Linux, MacOSX, may work on Windows, no tested.
# some syscall/flags not available on other OS(like Solaris), so not supported

def run_in_child(cmd):
    """run shell command in child process,
    non-blocking yields output.

    Args:
        cmd (string): command to run

    Returns:
        string, int: output line and exit value, output would be ``None'',
            exit value should use the last one.

    """
    r, w = os.pipe()
    pid = os.fork()

    exitvalue = None
    if pid == 0:
        # child
        os.dup2(r, 0)
        os.dup2(w, 1)
        os.dup2(w, 2)

        os.close(r)
        os.close(w)

        os.execl('/bin/bash', 'bash', '-c', cmd)
    else:
        f = fcntl.fcntl(r, fcntl.F_GETFL)
        fcntl.fcntl(r, fcntl.F_SETFL, f | os.O_NONBLOCK)

        line = b''
        while True:
            try:
                _ = os.read(r, 1)
                line += _
                if _ == b'\r':
                    _ = os.read(r, 1)
                    line += _
                    yield line.decode('UTF-8').strip(), exitvalue
                    line = b''
                if _ == b'\n':
                    yield line.decode('UTF-8').strip(), exitvalue
                    line = b''
            except OSError as e:
                try:
                    if type(e) == BlockingIOError:
                        pass
                    else:
                        raise
                except NameError:
                    if e.errno == errno.EAGAIN:
                        pass
                    else:
                        raise
            try:
                _pid, exitvalue = os.waitpid(-1, os.WNOHANG)
            except Exception as e:
                try:
                    if type(e) == ChildProcessError:
                        break
                    else:
                        raise
                except NameError:
                    if e.errno == errno.ECHILD:
                        break
                    else:
                        raise

        if line:
            yield line.decode('UTF-8').strip(), exitvalue

        yield None, exitvalue


def local(cmd, quiet=False, _raise=True):
    """run local command, prints output non-blocking

    Args:
        cmd (string): command to run
        quiet (bool): whether to surpress output
        _raise (bool): whether to raise RuntimeError when exit value is not 0
    """
    line = ''
    exitvalue = 0
    for line, exitvalue in run_in_child(cmd):
        if not quiet and line:
            print(line)

    if exitvalue != 0:
        raise RuntimeError('run local command failed: %s' % cmd)



local('python -u sleep.py')