Tips and Tricks #35: Use ValueTask for Hot Async Paths

Replace Task with ValueTask in frequently-called async methods that often complete synchronously.

Code Snippet

// Before: Always allocates a Task
public async Task GetCachedValueAsync(string key)
{
    if (_cache.TryGetValue(key, out int value))
        return value;
    return await FetchFromDatabaseAsync(key);
}

// After: Zero allocation when cached
public ValueTask GetCachedValueAsync(string key)
{
    if (_cache.TryGetValue(key, out int value))
        return new ValueTask(value);
    return new ValueTask(FetchFromDatabaseAsync(key));
}

Why This Helps

• Avoids Task allocation when result is immediately available
• Significant performance gain in cache-hit scenarios
• Backward compatible with existing async/await patterns

How to Test

• Benchmark with high cache-hit ratios
• Monitor allocation rate with dotMemory

When to Use

Caching layers, memoized computations, any async method with frequent synchronous completion.

Performance/Security Notes

ValueTask should only be awaited once. Don’t store or reuse ValueTask instances.

References

• https://devblogs.microsoft.com/dotnet/understanding-the-whys-whats-and-whens-of-valuetask/

Try this tip in your next project and share your results in the comments!