reliably forcing Guava map eviction to take place

Question

EDIT: I\'ve reorganized this question to reflect the new information that since became available.

This question is based on the responses to a quest

Answer 1

Yep, we've gone back and forth a few times on whether these cleanup tasks should be done on a background thread (or pool), or should be done on user threads. If they were done on a background thread, this would eventually happen automatically; as it is, it'll only happen as each segment gets used. We're still trying to come up with the right approach here - I wouldn't be surprised to see this change in some future release, but I also can't promise anything or even make a credible guess as to how it will change. Still, you've presented a reasonable use case for some kind of background or user-triggered cleanup.

Your hack is reasonable, as long as you keep in mind that it's a hack, and liable to break (possibly in subtle ways) in future releases. As you can see in the source, Segment.runCleanup() calls runLockedCleanup and runUnlockedCleanup: runLockedCleanup() will have no effect if it can't lock the segment, but if it can't lock the segment it's because some other thread has the segment locked, and that other thread can be expected to call runLockedCleanup as part of its operation.

Also, in r10, there's CacheBuilder/Cache, analogous to MapMaker/Map. Cache is the preferred approach for many current users of makeComputingMap. It uses a separate CustomConcurrentHashMap, in the common.cache package; depending on your needs, you may want your GuavaEvictionHacker to work with both. (The mechanism is the same, but they're different Classes and therefore different Methods.)