code: def send_ready(self):
          
          self.lock.acquire()
          try:
              if self.closed or self.eof_sent:
                  return True
              return self.out_window_size > 0
          finally:
              self.lock.release()
docs: Returns true if data can be written to this channel without blocking.
          This means the channel is either closed (so any write attempt would
          return immediately) or there is at least one byte of space in the
          outbound buffer. If there is at least one byte of space in the
          outbound buffer, a `send` call will succeed immediately and return
          the number of bytes actually written.
  
          :return:
              ``True`` if a `send` call on this channel would immediately succeed
              or fail