AsyncLocal.cs

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using System.Diagnostics.CodeAnalysis;
 
namespace System.Threading;
 
public sealed class AsyncLocal<T> : IAsyncLocal
{
    private readonly Action<AsyncLocalValueChangedArgs<T>> m_valueChangedHandler;
 
    public T Value
    {
        [return: MaybeNull]
        get
        {
            object localValue = ExecutionContext.GetLocalValue(this);
            if (localValue != null)
            {
                return (T)localValue;
            }
            return default(T);
        }
        set
        {
            ExecutionContext.SetLocalValue(this, value, m_valueChangedHandler != null);
        }
    }
 
    public AsyncLocal()
    {
    }
 
    public AsyncLocal(Action<AsyncLocalValueChangedArgs<T>>? valueChangedHandler)
    {
        m_valueChangedHandler = valueChangedHandler;
    }
 
    void IAsyncLocal.OnValueChanged(object previousValueObj, object currentValueObj, bool contextChanged)
    {
        T previousValue = ((previousValueObj == null) ? default(T) : ((T)previousValueObj));
        T currentValue = ((currentValueObj == null) ? default(T) : ((T)currentValueObj));
        m_valueChangedHandler(new AsyncLocalValueChangedArgs<T>(previousValue, currentValue, contextChanged));
    }
}