Basic Events Example

This sample demonstrates how to register a callback to receive Event messages from the DXL fabric. Once the the callback is registered, the sample sends a set number of Event messages to the fabric and waits for them all to be received by the callback.

The code for the sample is broken into two main sections.

Register Callback to Receive Events

The first section is responsible for registering an EventCallback for a specific topic. The add_event_callback() method by default will also subscribe to the topic.

#
# Register callback and subscribe
#

# Create and add event listener
class MyEventCallback(EventCallback):
    def on_event(self, event):
        with event_count_condition:
            # Print the payload for the received event
            print("Received event: " + event.payload.decode())
            # Increment the count
            event_count[0] += 1
            # Notify that the count was increment
            event_count_condition.notify_all()

# Register the callback with the client
client.add_event_callback(EVENT_TOPIC, MyEventCallback())

Send Events

The second section sends a set amount of Event messages via the send_event() method of the DxlClient.

It then waits for all of the events to be received by the EventCallback that was previously registered.

#
# Send events
#

# Record the start time
start = time.time()

# Loop and send the events
for event_id in range(TOTAL_EVENTS):
    # Create the event
    event = Event(EVENT_TOPIC)
    # Set the payload
    event.payload = str(event_id).encode()
    # Send the event
    client.send_event(event)

# Wait until all events have been received
with event_count_condition:
    while event_count[0] < TOTAL_EVENTS:
        event_count_condition.wait()

# Print the elapsed time
print("Elapsed time (ms): " + str((time.time() - start) * 1000))

Output

The output should appear similar to the following:

Received event: 0
Received event: 1
Received event: 2
Received event: 3
Received event: 4
Received event: 5

...

Received event: 994
Received event: 995
Received event: 996
Received event: 997
Received event: 998
Received event: 999
Elapsed time (ms): 441.999912262