Thread Pool configuration

[siva38]

Can the thread pool configuration be exposed for Expirer and Listener thread pools?

If a single threaded expirer may not be sufficient and an unbounded thread pool an over kill for certain cases, can the caller be asked to optionally supply thread pool executor instance?

[jhalterman]

Sure this could be configurable. I'm curious if you've actually hit a situation where the expiration thread, in particular, is unable to keep up with expirations. Has that happened? Any details?

[siva38]

I am planning to use this in an application where the TPS no's would be huge. I feel the single threaded expirer thread fits the scenario, but i saw a new thread created for clearing expired entries.

I tried to add 50 k entries with expiration of 3000 ms. After 5000 ms, i saw close to 23k entries cleared of cache.So i thought having an option to configure more threads for expiration would speed up the clean up process.

Also a bit hesitant to use the unbounded thread pool for listener. If these could be configured via builder it would be great

[jhalterman]

Thanks for the use case. I don't think it will be quite as straightforward as throwing more threads at it since there will be some lock contention when attempting to remove entries from the internal map.

[siva38]

Thanks. Can the listener thread be made configurable to prevent unbounded thread creation

[jhalterman]

Another option is we could use a fixed thread pool instead of cached. That opens up the potential for new problems... but what do you think?

[CodingFabian]

Here is a related use case: under very restricted resources, I might want to use inline expiration (on access/iteration) instead of having a thread work the expiration.

[CodingFabian]

and another "problem" if you use the ExpiringMap in an environment where the class could get unloaded, there is no "API-way" to stop the expirer and listenerService. thus leaking those services and threads

[lapo-luchini]

Yes, it generates:

org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [test] appears to have started a thread named [ExpiringMap-Expirer] but has failed to stop it. This is very likely to create a memory leak.

Being able to call EXPIRER.awaitTermination(…) would be nice.

[lapo-luchini]

I created PR #62 for that last part.

[jhalterman]

Interesting alternative... I left some comments on the PR. Interested to get feedback.