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CSharp · Console

/Program.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading.Tasks;

public class Program
{
	private static ConcurrentDictionary<string, Lazy<Task<DateTime>>> _cache = new();
	
	public static async Task Main()
	{
		Console.WriteLine("Hello World");

		await DoWork();

		Console.WriteLine("----------------------------------------");
		
		// Now wait 2 seconds.
		await Task.Delay(2000);
		
		// Lets run this all again .. and see if we get a different result? we should get the same cached value.
		await DoWork();
	}
	
	public static async Task DoWork()
	{
		List<Task<DateTime>> tasks = new();
		
		// Just so we can compare this time to the results times.
		var start = DateTime.UtcNow;
		Console.WriteLine("The Start: " + start + " / " + start.Ticks);
		
		// Setup all the tasks (which are not ran/executed yet).
		for(var i = 0; i < 10; i++)
		{
			tasks.Add(GetDateFromCache());
		}
		
		// Await for all the tasks to run and complete.
		await Task.WhenAll(tasks);
		
		// Display all the results from the tasks.
		foreach(var task in tasks)
		{
			Console.WriteLine(task.Result + " / " + task.Result.Ticks);
		}
		
		var end = DateTime.UtcNow;
		Console.WriteLine("The End: " + end + " / " + end.Ticks);
	}
	
	public static async Task<DateTime> GetDateFromCache()
	{
		var result = await _cache.GetOrAdd("someDateTime", new Lazy<Task<DateTime>>(async () => 
		{
			var someData = await GetDataFromSomeExternalDependency();
			
			return DateTime.UtcNow;
			
		})).Value;
		
		return result;
	}
								   
	public static async Task<int> GetDataFromSomeExternalDependency()
	{
		await Task.Delay(2000);
		
		return 1;
	}
}