0003 Understanding ValueTask in Async Programming

When working with async programming in C#, you’re likely familiar with Task. But did you know about ValueTask? It’s a performance optimization for scenarios where the result is often available synchronously.

Why use ValueTask?

• Task allocates an object on the heap, which can lead to unnecessary overhead if the operation completes synchronously.

• ValueTask is a struct, so it avoids heap allocation in such cases.

Example

public async ValueTask<int> CalculateAsync(int input)
{
    if (input < 0)
    {
        // Synchronous path (no heap allocation)
        return 0;
    }

    // Asynchronous path (heap allocation for Task)
    await Task.Delay(100);
    return input * 2;
}

When to use ValueTask:

• When the operation often completes synchronously.

• In high-performance scenarios where allocations matter.

Gotcha:

• Don’t use ValueTask if the operation is almost always asynchronous. The overhead of handling both paths might outweigh the benefits.