Do you know about the ThreadLocal<T> type that allows you to declare data storage that's associated with a specific thread?
If you know that, do you know about a similar concept but for async methods? AsyncLocal<T> is the type that allows you to bind a value to a specific asynchronous method call.
If an async method continues on a different thread, ThreadLocal<T> would not work in such a scenario. That's why AsyncLocal<T> is used.
See the example to get more familiar with how it works!
Docs 📑: https://learn.microsoft.com/en-us/dotnet/api/system.threading.asynclocal-1?view=net-8.0
AsyncLocal<string> asyncLocalContext = new();
asyncLocalContext.Value = "Value1";
var t1 = Method1("First call");
asyncLocalContext.Value = "Value2";
var t2 = Method1("Second call");
await Task.WhenAll(t1, t2);
return;
async Task Method1(string val)
{
Console.WriteLine($"Value before: {val}, {asyncLocalContext.Value}");
await Task.Delay(100);
Console.WriteLine($"Value after: {val}, {asyncLocalContext.Value}");
}
// Will produce the following output:
//
// Value before: First call, Value1
// Value before: Second call, Value2
// Value after: Second call, Value2
// Value after: First call, Value1