C# list where items have a TTL

For sake of a simple example, I'd like to have a list of strings. Each item in the list should "expire" 5 minutes after adding it to the list. Although there may not be an easy, built-in way to do this, I'd like to end up with a data structure who开发者_如何学Cse API feels like it "just works".

You might use it as follows:

var now = DateTime.now();
var list = new ListWithTTL<string>();
list.add("Bob", now);
list.add("Joe", now.AddMinutes(1));
list.add("Tom", now.AddMinutes(2));
list.add("Tim", now.AddMinutes(2));

Inspecting elements immediately would yield

["Bob", "Joe", "Tom", "Tim"]

A few minutes later it should yield

["Tom", "Tim"]

Eventually the list should be empty.

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You could use the MemoryCache class in .NET 4 which allows you to specify a TTL when you add an item.

Simple example:

MemoryCache cache = new MemoryCache("foo");
cache.Add("bar", "baz", DateTime.Now.AddSeconds(5));
var bar = cache["bar"];//returns "baz"
Thread.Sleep(TimeSpan.FromSeconds(6));
var expired = cache["bar"]; //returns null

While not providing you directly with a TTL list you could adapt this for your solution, no need to implement cache expiration yourself.

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You should be able to use SortedDictionary<DateTime, ...> and a custom IComparer<DateTime> that "reverses" the order of the dictionary so the oldest elements come first. Before returning elements from the dictionary, simply remove first N elements that are too old.

Of course, modifying collection "under the covers" when caller is expecting a simple read may lead to problems in multi-threaded environment, but this is a different topic...