Martin Tzvetanov Grigorov created WICKET-6800:
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Summary: Use LinkedHashSet instead of LinkedList for
AjaxRequestHandler#listeners
Key: WICKET-6800
URL: https://issues.apache.org/jira/browse/WICKET-6800
Project: Wicket
Issue Type: Improvement
Components: wicket
Affects Versions: 8.8.0, 9.0.0-M6
Reporter: Martin Tzvetanov Grigorov
Assignee: Martin Tzvetanov Grigorov
https://github.com/apache/wicket/pull/438
Urs Joss:
While migrating my project (see PR there) from the mocking library mockito to
mock, I ran into weird performance issues. The build time jumped from roughly
20 minutes to eventually more than 4 hours. I took some effort improving
various things in my own code (less mocking, more memory etc.) but did not
bring it down considerably until I addressed a bottleneck I found in wicket.
AjaxRequestHandler maintains a collection of listeners in a LinkedList. When
client code adds a new listener calling method addListener, it uses the
collection's method contains to assert we don't add a listener to the
collection twice. This doesn't scale well. For some reason, my setup with mockk
seems to add many more listeners than what my code did with mockito, so I ran
into this issue with continuously slower test executions.
I managed to temporarily resolve the problem in my project by plugging in my
own copy of AjaxRequestHandler where I swapped the collection type from
LinkedList to LinkedHashSet (calling setAjaxRequestTargetProvider in my
TestApplication). With this approach the total build time went down again to
20-30 minutes.
This PR serves the purpose of starting a discussion about whether this change
would be feasible to implement in wicket directly. To me, it is not apparent
why a LinkedList had been chosen initially. The LinkedHashSet performs much
better with contains and still preserves insertion order. If that latter should
turn out to be not relevant, we could even consider using a HashSet instead of
a linked HashSet, but I presume insertion order is important.
A separate topic on my side will be to figure out why my setup with mockito
seemed to work well while migrating to mockk surfaced this issue.
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