'Send a command and return immediately.
This is a lower level method than cmd().
This method will instruct the cmd-runner process
to execute a command, but this method will
immediately return.  You will need to use
``is_cmd_finished()`` to check that the command
is finished.
This method is useful if you want to record attributes
about the process while an operation is occurring.  For
example, if you want to instruct the cmd-runner process
to upload a 1GB file to S3 and you\'d like to record
the memory during the upload process, you can use
send_cmd() instead of cmd().'

def send_cmd(self, *cmd):

    cmd_str = ('    '.join(cmd) + '\n')
    cmd_bytes = cmd_str.encode('utf-8')
    self._popen.stdin.write(cmd_bytes)
    self._popen.stdin.flush()
