Provides the caller with means to remove and restore the current SynchronizationContext in an async method.

SynchronizationContextRemover.cs

using System;
using System.Runtime.CompilerServices;
using System.Threading;

/// <summary>
/// Provides the caller with means to remove and restore the current <see cref="SynchronizationContext"/> in an async method.
/// </summary>
public class SynchronizationContextRemover : INotifyCompletion
{
    private SynchronizationContextRemover()
    {

    }

    /// <summary>
    /// An awaitable <see cref="SynchronizationContext"/> remover.
    /// The current <see cref="SynchronizationContext"/> will be restored at the end of the caller's execution.
    /// </summary>
    public static SynchronizationContextRemover AwaitableRemover => new SynchronizationContextRemover();

    /// <summary>
    /// A disposable <see cref="SynchronizationContext"/> remover, meant to be used with the <see langword="using"/> statement.
    /// The current <see cref="SynchronizationContext"/> will be restored upon disposal of this instance.
    /// </summary>
    public static IDisposable DisposableRemover => new DisposableContextRemover();

    public bool IsCompleted => SynchronizationContext.Current == null;

    public void OnCompleted(Action continuation)
    {
        var previousContext = SynchronizationContext.Current;
        try
        {
            SynchronizationContext.SetSynchronizationContext(null);
            continuation();
        }
        finally
        {
            SynchronizationContext.SetSynchronizationContext(previousContext);
        }
    }

    public SynchronizationContextRemover GetAwaiter()
    {
        return this;
    }

    public void GetResult()
    {
            
    }
        
    private class DisposableContextRemover : IDisposable
    {
        private readonly SynchronizationContext _previousContext;

        internal DisposableContextRemover()
        {
            _previousContext = SynchronizationContext.Current;
            SynchronizationContext.SetSynchronizationContext(null);
        }

        public void Dispose()
        {
            SynchronizationContext.SetSynchronizationContext(_previousContext);
        }
    }
}