Task & Task<T>

Syntax

Task<T> task = SomeAsyncMethod();

Examples

Task<int> CalculateAsync()
{
    return Task.Run(() =>
    {
        Thread.Sleep(500);  // simulate CPU-bound work
        return 6 * 7;
    });
}

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

Task<int> task = Task.Run(() =>
{
    Thread.Sleep(300);
    return 100;
});

Console.WriteLine(task.IsCompleted);  // false, probably still running

int result = await task;
Console.WriteLine(task.IsCompleted);   // true
Console.WriteLine(result);              // 100

Task LogAsync(string message)
{
    Console.WriteLine(message);
    return Task.CompletedTask;  // no real async work needed, but interface requires Task
}

Task<int> GetCachedValueAsync(int cached)
{
    return Task.FromResult(cached);  // wraps an already-known value in a Task
}

await LogAsync("Started");
int value = await GetCachedValueAsync(99);
Console.WriteLine(value);

Best practices

• Use Task.Run() specifically for offloading CPU-bound work to a background thread - it is not needed for naturally async I/O operations like HttpClient calls, which are already non-blocking
• Prefer awaiting a Task directly over checking .IsCompleted in a polling loop - awaiting is more efficient and far simpler to reason about
• Use Task.FromResult() or Task.CompletedTask when implementing an async interface method that has no real asynchronous work to do
• Avoid using .Result or .Wait() to synchronously block on a Task - always prefer await, which does not risk deadlocks or block the calling thread

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