AsyncCache

Async cache uses an "async lock" (a semaphore) to prevent competing/simultaneous calls to the data source.

Usage

AsyncCache is not a singleton. If you want your cached key/values to be scoped as a singleton (also just generally speaking), I recommend using a dependency injector to instantiate AsyncCache.

The reason the cached key/values are scoped to the instance of AsyncCache is this way you can control both the TimeSpan and the scope of your key/values.

Usage Example Note: Don't use .Result from a task. Async functions should be called by async functions. This is just an example app to illustrate usage of AsyncCache. This example app is synchronous..so maybe a bad example but it should still illistrate the usage.

using Cache;
using System;
using System.Threading.Tasks;
        
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var random = new Random();
            var cache = new AsyncCache();
        
            Console.WriteLine("Not Cached:");
            for (var i = 0; i < 5; i++)
                Console.WriteLine(random.Next(0, 5));
        
            Console.WriteLine("\nCached:");
            for (var i = 0; i < 5; i++)
                Console.WriteLine(cache.Get(
                    key: "random integer",
                    dataSource: () => Task.FromResult(random.Next(0, 5))).Result);
        
            Console.ReadKey();
        }
    }
}

Example App Output:

    Not Cached:
    4
    2
    2
    4
    0
    
    Cached:
    2
    2
    2
    2
    2

Here is example usage from unit tests (below). Did I mention how simple it is?

[TestInitialize]
public void Setup()
{
    _cache = new AsyncCache();
}

[TestMethod]
public async Task ShouldReturnResultFromDataSourceTask()
{
    //Arrange
    //Act
    int result = await _cache.Get("some key", () => Task.FromResult(2));

    //Assert
    result.Should().Be(2);
}
        
[TestMethod]
public async Task ShouldLockToPreventRaceCondition()
{
    var tcs1 = new TaskCompletionSource<int>();
    var tcs2 = new TaskCompletionSource<int>();

    int? result1 = null;
    int? result2 = null;
    var get1 = _cache.Get(key: "key1", dataSource: () => tcs1.Task).ContinueWith(t => result1 = t.Result);
    var get2 = _cache.Get(key: "key1", dataSource: () => tcs2.Task).ContinueWith(t => result2 = t.Result);

    tcs1.SetResult(1);
    tcs2.SetResult(2);

    await Task.WhenAll(get1, get2);

    result1.Should().Be(1, "because this is the initial value inserted into the cache.");
    result2.Should().Be(1, "because the previous/parallel request should've already inserted 1");
}