4.4.2 Lapsed Listener Problem
A notification system introduces a potential for memory leaks known as “Lapsed listener problem”. It occurs when a listener registers to a notifier, then goes out of scope without unsubscribing. The listener is never garbage collected due to the permanence of the notification connection. It is technically still receiving notifications, which may introduce additional problems if these notifications are expensive to honor. In languages without GC, if the listener is deleted, the notifier can now hold a reference to freed memory, potentially resulting in a crash.
There are various options to solve this problem. The first is to make sure the listener is correctly unregistered before going out of scope or released.
The second option is to have a notification system using weak references.
problem can exist also with callbacks that are closures, or when exceptions are stored.