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Editorial Team
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Asked: 2026-05-22T01:23:46+00:00

I want to implement a HashTable (or mabybe a HashSet or Dictionary ) which

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I want to implement a HashTable (or mabybe a HashSet or Dictionary) which has unique members which expire after a while. For example:

// Items expire automatically after 10 seconds (Expiration period = 10 sec)
bool result = false;
// Starting from second 0
result = MyHashSet.Add("Bob");   // second 0 => true
result = MyHashSet.Add("Alice"); // second 5 => true
result = MyHashSet.Add("Bob");   // second 8 => false (item already exist)
result = MyHashSet.Add("Bob");   // second 12 => true (Bob has expired)

How to do that in a thread-safe manner with lowest costs?

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1 Answer

  1. Editorial Team

    You could create you own Hash Table where each item contains a creation time and a timespan.
    In the indexer where you try to return the value return null if the lifetime of the item has expired. And remove the item. A background thread that removes items from the table will not ensure you that you will never return an expired item without this. Then you can create a thread that does this just to remove expired items altogether to minimize memory consumption if a lot of items are never acessed.

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