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Editorial Team
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Asked: 2026-05-29T17:08:59+00:00

So here I am implementing some caching layer. Particurally I am stuck with ConcurrentDictionary<SomeKey,HashSet<SomeKey2>>

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So here I am implementing some caching layer. Particurally I am stuck with

ConcurrentDictionary<SomeKey,HashSet<SomeKey2>>

I need to ensure that operations on HashSet are threadsafe too (ergo Update is threadsafe). Is it possible in any simple way or do I have to synchronize in the UpdateFactory delegate? If the answer is yes (which I presume) did any one of You encountered this problem before and solved it?

I want to avoid ConcurrentDictionary of ConcurrentDictionaries because they allocate a lot of synchronization objects and I potentially have around a million entries in this thing, so I want to have less pressure in on the GC.
HashSet was chosen because it guarantees amortized constant cost of insertion,deletion and access.

The aforementioned structure will be used as a index on a larger data set with to columns as a key (SomeKey and Somekey2) much like a database index.

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  1. Editorial Team

    Ok so finally I decided to go with Immutable set and lock striping because it is reasonably simple to implement and understand. If I will need more performance on the writes (no copying the whole hash set on insert) I will implement reader/writer locks with striping – which should be fine anyway.
    Thanks for suggestions.

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