In
computer programming
Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...
, the lapsed listener problem is a common source of
memory leaks for
object-oriented programming languages, among the most common ones for
garbage collected languages.
Memory Loiterers in Java
Ethan Henry and Ed Lycklama
It originates in the observer pattern
In software design and software engineering, the observer pattern is a software design pattern in which an object, called the ''subject'' (also known as ''event source'' or ''event stream''), maintains a list of its dependents, called observers (a ...
, where observers (or listeners) register with a subject (or publisher) to receive events. In basic implementation, this requires both explicit registration and explicit deregistration, as in the dispose pattern, because the subject holds strong references
A reference is a relationship between Object (philosophy), objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. ...
to the observers, keeping them alive. The leak happens when an observer fails to unsubscribe from the subject when it no longer needs to listen. Consequently, the subject still holds a reference to the observer which prevents it from being garbage collected — including all other objects it is referring to — for as long as the subject is alive, which could be until the end of the application.
This causes not only a memory leak, but also a performance degradation with an "uninterested" observer receiving and acting on unwanted events. This can be prevented by the subject holding weak references to the observers, allowing them to be garbage collected as normal without needing to be unregistered.
References
{{Memory management navbox
Software bugs
Software anomalies