async and await

Syntax

async Task MethodName() {\n  await SomeAsyncOperation();\n}

Examples

async Task GreetAfterDelayAsync()
{
    Console.WriteLine("Starting...");
    await Task.Delay(1000);  // pauses here without blocking the thread
    Console.WriteLine("One second later!");
}

await GreetAfterDelayAsync();

async Task<int> GetNumberAsync()
{
    await Task.Delay(500);
    return 42;
}

int result = await GetNumberAsync();
Console.WriteLine(result);  // 42

// Synchronous: blocks the calling thread entirely for 2 seconds
void BlockingWait()
{
    Thread.Sleep(2000);
    Console.WriteLine("Done (blocked the thread the whole time)");
}

// Asynchronous: frees the thread to do other work while waiting
async Task NonBlockingWaitAsync()
{
    await Task.Delay(2000);
    Console.WriteLine("Done (thread was free to do other work)");
}

await NonBlockingWaitAsync();

async Task<string> FetchDataAsync()
{
    Console.WriteLine("Step 1: connecting...");
    await Task.Delay(300);

    Console.WriteLine("Step 2: downloading...");
    await Task.Delay(300);

    return "data loaded";
}

string data = await FetchDataAsync();
Console.WriteLine(data);

Best practices

• Name async methods with an "Async" suffix (GetDataAsync, not GetData) - a strong, widely followed C# convention
• Use async Task instead of async void for any method except top-level event handlers - async void methods cannot be awaited and make error handling much harder
• Await asynchronous operations all the way up the call chain rather than blocking on them with .Result or .Wait(), which can cause deadlocks in some contexts (like UI apps)
• Reserve async/await for genuinely I/O-bound work (network, disk, database) - it does not speed up CPU-bound computation on its own

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation