MemoryCache Thread Safety, Is Locking Necessary?

Question

For starters let me just throw it out there that I know the code below is not thread safe (correction: might be). What I am struggling with is finding an implementation that

Answer 1

While MemoryCache is indeed thread safe as other answers have specified, it does have a common multi threading issue - if 2 threads try to Get from (or check Contains) the cache at the same time, then both will miss the cache and both will end up generating the result and both will then add the result to the cache.

Often this is undesirable - the second thread should wait for the first to complete and use its result rather than generating results twice.

This was one of the reasons I wrote LazyCache - a friendly wrapper on MemoryCache that solves these sorts of issues. It is also available on Nuget.