def poll(self, conn):
        """Poll DB socket and process async tasks."""
        while 1:
            state = conn.poll()
            if state == psycopg2.extensions.POLL_OK:
                while conn.notifies:
                    notify = conn.notifies.pop()
                    self.logger.info(
                        "Got NOTIFY (pid=%d, payload=%r)",
                        notify.pid, notify.payload,
                    )

                    # read the header and check seq/fin.
                    hdr, chunk = notify.payload.split('|', 1)
                    # print('RECEIVE: %s' % hdr)
                    header = ejson.loads(hdr)
                    uuid = header['uuid']
                    size, chunks = self.chunks.setdefault(uuid, [0, {}])
                    if header['fin']:
                        size = self.chunks[uuid][0] = header['seq']

                    # stash the chunk
                    chunks[header['seq']] = chunk

                    if len(chunks) != size:
                        # haven't got all the chunks yet
                        continue  # process next NOTIFY in loop

                    # got the last chunk -> process it.
                    data = ''.join(
                        chunk for _, chunk in sorted(chunks.items())
                    )
                    del self.chunks[uuid]  # don't forget to cleanup!
                    data = ejson.loads(data)
                    sender = data.pop('_sender', None)
                    tx_id = data.pop('_tx_id', None)
                    for connection_id in data.pop('_connection_ids'):
                        try:
                            websocket = self.connections[connection_id]
                        except __HOLE__:
                            continue  # connection not in this process
                        if connection_id == sender:
                            websocket.send(data, tx_id=tx_id)
                        else:
                            websocket.send(data)
                break
            elif state == psycopg2.extensions.POLL_WRITE:
                gevent.select.select([], [conn.fileno()], [])
            elif state == psycopg2.extensions.POLL_READ:
                gevent.select.select([conn.fileno()], [], [])
            else:
                self.logger.warn('POLL_ERR: %s', state)
dataset/ETHPy150Open django-ddp/django-ddp/dddp/postgres.py/PostgresGreenlet.poll