Playing with sync context and async

Program.cs

using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace SyncContext
{
    class Program
    {
        static void Main()
        {
            Run();
            SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
            Run();

            Console.Read();
        }

        private static void Run()
        {
            Console.WriteLine("=== Start");
            OutputSyncContext();
            Console.WriteLine("== Wait");
            Start().Wait();
            Console.WriteLine("== Wait long-running task");
            Task.Factory.StartNew(async () => await Start(), TaskCreationOptions.LongRunning).Wait();
        }

        private static async Task Start()
        {
            OutputSyncContext();
            var tasks = Enumerable.Range(1, 10).Select(i => Run(i)).ToArray();
            await Task.WhenAll(tasks);
        }

        private static async Task Run(int i)
        {
            Console.WriteLine("{0}: Before continuation {1}", Thread.CurrentThread.ManagedThreadId, i);
            await Task.Delay(200);
            Console.WriteLine("{0}: After continuation {1}", Thread.CurrentThread.ManagedThreadId, i);
        }

        private static void OutputSyncContext()
        {
            if (SynchronizationContext.Current == null)
                Console.WriteLine("No Sync context");
            else
                Console.WriteLine("Sync context hash code: " + SynchronizationContext.Current.GetHashCode());
        }
    }
}

=== Start
No Sync context
== Wait
No Sync context
9: Before continuation 1
9: Before continuation 2
9: Before continuation 3
9: Before continuation 4
9: Before continuation 5
9: Before continuation 6
9: Before continuation 7
9: Before continuation 8
9: Before continuation 9
9: Before continuation 10
11: After continuation 10
13: After continuation 8
11: After continuation 7
11: After continuation 5
11: After continuation 4
11: After continuation 3
11: After continuation 2
11: After continuation 1
13: After continuation 6
12: After continuation 9
== Wait long-running task
No Sync context
15: Before continuation 1
15: Before continuation 2
15: Before continuation 3
15: Before continuation 4
15: Before continuation 5
15: Before continuation 6
15: Before continuation 7
15: Before continuation 8
15: Before continuation 9
15: Before continuation 10
=== Start
Sync context hash code: 57352375
== Wait
Sync context hash code: 57352375
9: Before continuation 1
9: Before continuation 2
9: Before continuation 3
9: Before continuation 4
9: Before continuation 5
9: Before continuation 6
9: Before continuation 7
9: Before continuation 8
9: Before continuation 9
9: Before continuation 10
12: After continuation 4
13: After continuation 2
12: After continuation 1
11: After continuation 3
14: After continuation 5
13: After continuation 1
13: After continuation 7
13: After continuation 6
14: After continuation 8
11: After continuation 10
12: After continuation 9
13: After continuation 10
11: After continuation 9
11: After continuation 6
11: After continuation 5
11: After continuation 4
13: After continuation 3
12: After continuation 8
11: After continuation 2
14: After continuation 7
== Wait long-running task
No Sync context
17: Before continuation 1
17: Before continuation 2
17: Before continuation 3
17: Before continuation 4
17: Before continuation 5
17: Before continuation 6
17: Before continuation 7
17: Before continuation 8
17: Before continuation 9
17: Before continuation 10
11: After continuation 10
16: After continuation 9
16: After continuation 4
16: After continuation 3
16: After continuation 2
12: After continuation 7
14: After continuation 8
16: After continuation 1
11: After continuation 5
13: After continuation 6