def reapProcess(self):
        """
        Try to reap a process (without blocking) via waitpid.

        This is called when sigchild is caught or a Process object loses its
        "connection" (stdout is closed) This ought to result in reaping all
        zombie processes, since it will be called twice as often as it needs
        to be.

        (Unfortunately, this is a slightly experimental approach, since
        UNIX has no way to be really sure that your process is going to
        go away w/o blocking.  I don't want to block.)
        """
        try:
            try:
                pid, status = os.waitpid(self.pid, os.WNOHANG)
            except OSError as e:
                if e.errno == errno.ECHILD:
                    # no child process
                    pid = None
                else:
                    raise
        except:
            log.msg('Failed to reap %d:' % self.pid)
            log.err()
            pid = None
        if pid:
            self.processEnded(status)
            unregisterReapProcessHandler(pid, self)

        Try to reap a process (without blocking) via waitpid.

        This is called when sigchild is caught or a Process object loses its
        "connection" (stdout is closed) This ought to result in reaping all
        zombie processes, since it will be called twice as often as it needs
        to be.

        (Unfortunately, this is a slightly experimental approach, since
        UNIX has no way to be really sure that your process is going to
        go away w/o blocking.  I don't want to block.)
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/process.py