Does WeakReference make a good cache?

c# .net caching garbage-collection weak-references
Rauhotz picture Rauhotz · May 30, 2009 · Viewed 9.8k times · Source

i have a cache that uses WeakReferences to the cached objects to make them automatically removed from the cache in case of memory pressure. My problem is that the cached objects are collected very soon after they have been stored in the cache. The cache runs in a 64-Bit application and in spite of the case that more than 4gig of memory are still available, all the cached objects are collected (they usually are stored in the G2-heap at that moment). There are no garbage collection induced manually as the process explorer shows.

What methods can i apply to make the objects live a litte longer?

Answer

jrista picture jrista · May 30, 2009

Using WeakReferences as the primary means of referencing cached objects is not really a great idea, because as Josh said, your at the mercy of any future behavioral changes to WeakReference and the GC.

However, if your cache needs any kind of resurrection capability, use of WeakReferences for items that are pending purge is useful. When an item meets eviction criteria, rather than immediately evicting it, you change its reference to a weak reference. If anything requests it before it is GC'ed, you restore its strong reference, and the object can live again. I have found this useful for some caches that have hard to predict hit rate patterns with frequent enough "resurrections" to be beneficial.

If you have predictable hit rate patterns, then I would forgoe the WeakReference option and perform explicit evictions.

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