René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Unsubscribe from topic safely","articleBody":"Currently, there is no safe way to unsubscribe from a topic. If the user calls `dispose()` on a `Subscription`, then it will destroy the native subscription (effectively unsubscribing), but the `Node` is not aware of the subscriptions disposal. E.g. [getSubscriptions](https://github.com/ros2-java/ros2_java/blob/1190aeb909e051e79b2b43325f924f42e5c96160/rcljava/src/main/java/org/ros2/rcljava/node/NodeImpl.java#L227-L229) will return disposed subscriptions that may be [accessed by executors](https://github.com/ros2-java/ros2_java/blob/1190aeb909e051e79b2b43325f924f42e5c96160/rcljava/src/main/java/org/ros2/rcljava/executors/BaseExecutor.java#L170) leading an exception:\r\n\r\n    org.ros2.rcljava.exceptions.RCLException: Failed to add subscription to wait set\r\n\r\nI think we need a way to safely remove `Subscription` (and `Publisher`) objects from a node. Whether that is through the existing `Disposable` interface or API added to the node (e.g. `removeSubscription`).\r\n\r\n## Implementation considerations\r\n\r\nI think having the node detect when a subscription has been disposed (perhaps using [WeakReference](https://docs.oracle.com/javase/7/docs/api/java/lang/ref/WeakReference.html)) would be nice as I don't think it would require additional API. ","author":{"url":"https://github.com/jacobperron","@type":"Person","name":"jacobperron"},"datePublished":"2020-05-01T17:46:16.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/105/ros2_java/issues/105"}