How to Ensure Single Execution of Asynchronous Initialization in C#?

Guaranteeing Single Execution of Asynchronous Initialization in C#

This article addresses the challenge of ensuring a class's asynchronous initialization, via its InitializeAsync() method, executes only once, even with concurrent calls from multiple threads.

One approach uses SemaphoreSlim:

<code class="language-csharp">public class MyService : IMyService
{
    private readonly SemaphoreSlim mSemaphore = new SemaphoreSlim(1, 1);
    private bool mIsInitialized;

    public async Task InitializeAsync()
    {
        if (!mIsInitialized)
        {
            await mSemaphore.WaitAsync();

            if (!mIsInitialized)
            {
                await DoStuffOnlyOnceAsync();
                mIsInitialized = true;
            }

            mSemaphore.Release();
        }
    }

    private Task DoStuffOnlyOnceAsync()
    {
        return Task.Run(() =>
        {
            Thread.Sleep(10000);
        });
    }
}</code>

A more elegant solution leverages AsyncLazy<T>:

<code class="language-csharp">public class AsyncLazy<T> : Lazy<Task<T>>
{
    public AsyncLazy(Func<T> valueFactory) :
        base(() => Task.Run(valueFactory)) { }

    public AsyncLazy(Func<Task<T>> taskFactory) :
        base(() => Task.Run(() => taskFactory())) { }

    public TaskAwaiter<T> GetAwaiter() { return Value.GetAwaiter(); }
}</code>

Usage example:

<code class="language-csharp">private AsyncLazy<bool> asyncLazy = new AsyncLazy<bool>(async () =>
{
    await DoStuffOnlyOnceAsync();
    return true;
});</code>

Note: A boolean placeholder is used because DoStuffOnlyOnceAsync() lacks a return type.

For a refined AsyncLazy<T> implementation, refer to Stephan Cleary's blog post: https://www.php.cn/link/366c0196895c9eeaa75992bacac60426

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