Async Lazy

AsyncLazy<T> provides support for asynchronous lazy initialization. This is asynchronous alternative to Lazy<T> from .NET library.

This class is useful when some object requires resource-intensive asynchronous initialization. Additionally, it is possible to erase initialized object and force initialization again using Reset method. To do that, AsyncLazy should be created as resettable object through passing appropriate argument into its constructor.

The following example demonstrates how to use asynchrous lazy initialization:

using DotNext.Threading;

class DataRepository
{
	private readonly AsyncLazy<DataCache> cache;
	private readonly IDbConnection connection;
	
	public DataRepository(IDbConnection connection)
	{
		this.connection = connection;
		cache = new AsyncLazy<DataCache>(token => InitCache(connection, token));
	}

	private static async Task<DataCache> InitCache(IDbConnection connection, CancellationToken token)
	{
		//initialize cache asynchronously
	}

	public async Task<User> GetUserByIdAsync(long id, CancellationToken token)
	{
		var cache = await cache.WithCancellation(token);
		if(cache.ContainsUser(id))
			return cache.GetUser(id);
		else
			return GetUserByIdNonCached(connection, id);
	}

	private static User GetUserByIdNonCached(IDbConnection connection, long id)
	{
		//database access
	}
}