What's the difference between MemoryCache.Add and MemoryCache.Set?

Question

I read the MSDN documentation but didn't really understand it.

I believe that the behavior of Set is "replace existing, or add" (atomically).

Is that correct?

score 197 · Accepted Answer · edited Nov 15 '16 at 07:00

197

Add does nothing (returns false) if there is already a value for that key. Set does an insert or update, as necessary.

Remove + Add would leave a gap in the middle when another thread querying that key would get no clue (Set does not; the swap is typically atomic); as such, while Set has the same end result as Remove + Add, the mechanism difference is important since it could impact other callers.

For example of Add:

Return Value

Type: System.Boolean true if insertion succeeded, or false if there is an already an entry in the cache that has the same key as key.

edited Nov 15 '16 at 07:00

CodeNotFound

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answered Jan 15 '12 at 08:46

Marc Gravell

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Does `set` replaces Policy if item exists? – T.S. Aug 06 '19 at 04:17
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I just saw your almost year old message, I am working on similar issue. All SET overloads require a Policy, so the answer is yes. – user2223142 May 24 '20 at 21:23
if I use Add function on an expired cache? will it be replaced with the updated CacheItem? – aj go Jan 29 '21 at 13:11

What's the difference between MemoryCache.Add and MemoryCache.Set?

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