Documentation doesn't clearly state what happens after an abort

By @hamishwillee’s suggestion, I’m opening this because I was trying to figure out what happens after a connection abort (i.e. heartbeat_timeout is exceeded), and the documentation does not make it clear. After looking through dronekit/init.py, I see on lines 1099-1102:

                if self._heartbeat_error and self._heartbeat_error > 0 and time.time(
                ) - self._heartbeat_lastreceived > self._heartbeat_error:
                    raise APIException('No heartbeat in %s seconds, aborting.' %
                                       self._heartbeat_error)

Looking at dronekit/mavlink.py, I can see that the exception will cause the handler thread to exit:

            try:
                while True:
                    # Downtime
                    time.sleep(0.05)

                    # Loop listeners.
                    for fn in self.loop_listeners:
                        fn(self)

…

            except APIException as e:
                errprinter('>>> ' + str(e.message))
                self._alive = False
                self.master.close()
                self._death_error = e
                return

I think the documentation could be improved by stating that the abort will cause the connection to permanently close (while a heartbeat_warning will not), and that if this behavior is not desired, to set the timeout to a large value. If an abort occurs, @hamishwillee suggested that the only recourse would be a reconnect, and the documentation should state this. Also, in the case of an abort, I’m not sure how to detect it from a script (to go about doing a reconnect).

One other issue, is that a reconnect would issue a new vehicle object, but all the decorated message/attribute listeners on the top level (say in a module) would have already been initialized, and would not be updated. Meaning if you expect a reconnect, you would need to re-declare all your decorated handlers with the new vehicle object (probably inside an initialization function).

Edit to illustrate my point:

# Is only called when the module is imported, cannot be updated...
@vehicle.on_attribute('location')
def listener(...)
    ...

def initialize(vehicle):
    # Called each time we call initialize. Sets up listeners on new vehicle
    @vehicle.on_attribute('location') 
    def listener(...)
         ...

It might also be worth considering if it should be possible to disable it completely (say, pass in a timeout of -1).

[Evidlo]

Here’s a working solution, but too much of a hack in my opinion:

from dronekit import connect
from time import sleep

def last_heartbeat_callback(vehicle, attr_name, last_heartbeat):
    if last_heartbeat > 5:
        print('last_heartbeat > 5, reconnecting')
        vehicle._handler.master.close()
        pixhawk_connect()

def pixhawk_connect():
    vehicle = connect("tcp:localhost:14550", heartbeat_timeout=50)
    vehicle.add_attribute_listener('last_heartbeat', last_heartbeat_callback)

pixhawk_connect()

while True:
    sleep(1)

[Evidlo]

Has anything changed here? I haven’t found a decent way to detect an abort so that I can reconnect to the Pixhawk if it loses power. Ideally there would be a vehicle.aborted attribute that I could attach a listener to.

Here’s one failed attempt at a solution:

from dronekit import connect
from time import sleep

def last_heartbeat_callback(vehicle, attr_name, last_heartbeat):
    if last_heartbeat > 5:
        print('last_heartbeat > 5, reconnecting')
        vehicle.close()
        pixhawk_connect()

def pixhawk_connect():
    vehicle = connect("tcp:localhost:14550", heartbeat_timeout=50)
    vehicle.add_attribute_listener('last_heartbeat', last_heartbeat_callback)

pixhawk_connect()

while True:
    sleep(1)

But I get

>>> Exception in attribute handler for last_heartbeat
>>> cannot join current thread

on vehicle.close(), probably because I’m trying to close vehicle from inside its own callback.