Question

Well, I've tried to use one channel and topic A to control whether to subscribe to another topic B。So when handling B‘s callback，and in A's callback I am trying to shutdown subscriber to B , the program then block in the shutdown ,even B's callback is executed over ， the shutdown method is still in block，Ctrl + C even can't kill it 。 Or in another word, is there a safe method to stop a runtime subscriber ?

Asked by sunjay on 2023-02-09 01:53:10 UTC

Answer 1

is there a safe method to stop a runtime subscriber

Yes: do it from outside the subscribe callback.

One approach is, In your main thread, create a "while loop", and inside the loop check a flag to determine if it should unregister the subscriber. This loop does not need to execute very often - it should spend most of its time sleeping (so you don't waste CPU cycles.) If your ros node shows 100% CPU usage, you did it wrong.

while not rospy.is_shutdown():
    if stop_my_sub:
        my_sub.unregister()
        my_sub = None
        stop_my_sub = False
    rospy.sleep(0.250)

However, it is usually a bad idea for a node to unregister a subscriber. It's easy to lose messages if the node frequently subscribes & unsubscribes a topic. A better design approach is to keep the subscriber active, and have it check a flag inside the callback to determine whether to ignore the new message or to process it.

Asked by Mike Scheutzow on 2023-02-10 08:23:27 UTC

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Thanks for answer and advise, I've tried this method and it did work.

Asked by sunjay on 2023-02-12 01:52:43 UTC

Is it able to shutdown a Subscriber when its callback executing?

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