First pass at introducing kestrel and refactoring to make the RESTAPI be its own package.

Duplicati.Library.RestAPI/EventPollNotify.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Duplicati.Server
+{
+    /// <summary>
+    /// This class handles synchronized waiting for events
+    /// </summary>
+    public class EventPollNotify
+    {
+        /// <summary>
+        /// The lock that grants exclusive access to control structures
+        /// </summary>
+        private readonly object m_lock = new object();
+        /// <summary>
+        /// The current eventID
+        /// </summary>
+        private long m_eventNo = 0;
+        /// <summary>
+        /// The list of subscribed waiting threads
+        /// </summary>
+        private readonly Queue<System.Threading.ManualResetEvent> m_waitQueue = new Queue<System.Threading.ManualResetEvent>();
+
+        /// <summary>
+        /// An eventhandler for subscribing to event updates without blocking
+        /// </summary>
+        public event EventHandler NewEvent;
+
+        /// <summary>
+        /// Gets the current event ID
+        /// </summary>
+        public long EventNo { get { return m_eventNo; } }
+
+        /// <summary>
+        /// Call to wait for an event that is newer than the current known event
+        /// </summary>
+        /// <param name="eventId">The last known event id</param>
+        /// <param name="milliseconds">The number of milliseconds to block</param>
+        /// <returns>The current event id</returns>
+        public long Wait(long eventId, int milliseconds)
+        {
+            System.Threading.ManualResetEvent mre;
+            lock (m_lock)
+            {
+                //If a newer event has already occured, return immediately
+                if (eventId != m_eventNo)
+                    return m_eventNo;
+
+                //Otherwise register this thread as waiting
+                mre = new System.Threading.ManualResetEvent(false);
+                m_waitQueue.Enqueue(mre);
+            }
+
+            //Wait until we are signalled or the time has elapsed
+            mre.WaitOne(milliseconds, false);
+            return m_eventNo;
+        }
+
+        /// <summary>
+        /// Signals that an event has occurred and notifies all waiting threads
+        /// </summary>
+        public void SignalNewEvent()
+        {
+            lock (m_lock)
+            {
+                m_eventNo++;
+                while (m_waitQueue.Count > 0)
+                    m_waitQueue.Dequeue().Set();
+            }
+
+            if (NewEvent != null)
+                NewEvent(this, null);
+        }
+    }
+}