I've got a Guava
(or rather, I am migrating from
) and the values represent long-running jobs. I'd like to add
behavior to the cache, as it's the best way to clean it up; however, the job may still be running even though it hasn't been accessed via the cache in some time, and in that case I need to prevent it from being removed from the cache. I have three questions:
- Is it safe to reinsert the cache entry that's being removed during the
- If so, is it threadsafe, such that there's no possible way the
could produce a second value for that key while the
callback is still happening in another thread?
- Is there a better way to achieve what I want? This isn't strictly/only a "cache" - it's critical that one and only one value is used for each key - but I also want to cache the entry for some time after the job it represents is complete. I was using
before and the behaviors I need are now deprecated in that class. Regularly pinging the map while the jobs are running is inelegant, and in my case, infeasible. Perhaps the right solution is to have two maps, one without eviction, and one with, and migrate them across as they complete.
I'll make a feature request too - this would solve the problem: allow individual entries to be locked to prevent eviction (and then subsequently unlocked).
[Edit to add some details]:
The keys in this map refer to data files. The values are either a running write job, a completed write job, or - if no job is running - a read-only, produced-on-lookup object with information read from the file. It's important that there is exactly zero or one entry for each file. I could use separate maps for the two things, but there would have to be coordination on a per-key basis to make sure only one or the other is in existence at one time. Using a single map makes it simpler, in terms of getting the concurrency correct.