Times out after 10s

[jason-cso]

Seems like RTDE expects you to poll it continuously after you connect if you want fresh data. It'd be good if that was clearly called out in the docs.

If I do this:

rtde.connect()
time.sleep(11)
rtde.receive()

I get errors like received 0 bytes from Controller, probable cause: Controller has stopped or received 0 bytes from Controller. Also, I'll often get two stale messages before it notices the disconnect.

[gsim-inbolt]

Got the same issue here, ended up calling rtde.receive() at 500 Hz in a thread.
I wonder if this is by design of the RTDE protocol or caused by a mistake in this implementation though

[michal-milkowski]

You're both right, after starting connection controller will send rt data, and python client is expected to read it. I'll add a line in documentation (as minimum).

[michal-milkowski]

I'm thinking about either adding an example with thread specifically for reading socket, or adding a method to library that clears receive buffer. Method would need to be called periodically.
What would be easier to use?

[jason-cso]

They both sound pretty useful. Could we have both? BTW this is how I solved it. Not very elegant, but I'm not latency sensitive.

    def receive(self):
        for i in range(10):
            now = time.monotonic()
            try:
                # RTDE seems to time out after 10s, so we'll use 8s for a little margin
                if now - self.last_receive > 8.0:
                    log.info("Calling RTDE receive() 2 extra times to notice likely disconnect")
                    results = self.rtde.receive(binary=False)
                    results = self.rtde.receive(binary=False)

                results = self.rtde.receive(binary=False)
                self.last_receive = time.monotonic()
                return results
            except rtde.RTDEException as e:
                log.error("RTDE error on attempt %d: %s", i, e)
                self.rtde.disconnect()
                self._setup()

        raise Exception("Couldn't receive")

[michal-milkowski]

That makes a lot of sense. What would be the use case for ignoring incoming data?

[jason-cso]

Some things are only accessible by rtde (like the registers and joints), so I have to use it even though I don't need its realtime nature. I did consider using a thread to keep it drained, but python's global interpreter lock and making sure I got setup/teardown right dissuaded me.

[gsim-inbolt]

A method clearing the whole buffer would be quite interesting, but the thread fulfills a different purpose imo so as @jason-cso mentioned having both would not feel redundant. Doing it cleanly with a thread certainly takes more effort though.

[sri331]

Got the same issue here, ended up calling rtde.receive() at 500 Hz in a thread. I wonder if this is by design of the RTDE protocol or caused by a mistake in this implementation though

I am trying to add a thread to handle connection lost issue but not successful ... Could you share sample code for the thread you implemented?

[gsim-inbolt]

Something similar to what we had would be:

def get_state():
    while not stop_event.is_set():
        state = rtde.receive()
        if state is None:
            logger.error("No data received, shutting down connection...")
            rtde.send_pause()
            rtde.disconnect()
            raise RTDEException
        if state_queue.full():
            state_queue.get_nowait()
        state_queue.put(state)
    return

robot_thread = th.Thread(target=get_state)
robot_thread.start()

[tomek2311]

I am running into smiliar (but different) 10 sec timeout issue. Here is the scenario:
I contenatized RTDE solution (based example provided in this repo) so that I can get access to UR states. When I run it from command line line (say: docker run --rm -dit -e ROBOT_IP="192.168.254.171" --name rtdeplugin rtdeplugin:latest) everything is fine - programs stays up.
On the other hand, when I try to run it as a service (using systemd), executng same command, it runs for 10 seconds and exists, systemd starts it again (since I specified to run forever), and the process continues forrever.

Did anyone tried to run rtde controller solution as a service, and was sucessful ?
Thanks, Tomasz

[sri331]

Thanks gsim-inbolt . The thread is useful. I am not sure if rtde class is thread safe not resulting in race condition. I am using a thread to make the connection active but some times it is giving below issue and going to infinite loop.
“Unknown package command: 0”