# HG changeset patch
# User cin
# Date 1518299391 -10800
# Node ID 7c7e9ad6fe4a136b3565cc702420267b8610c8d4
# Parent  9f63dade3a40ef353cf81f7712e4877424b7ba5b
Prerelease version of RunnableComponent
Added draft messaging interfaces
Added more more helpers to Xml/SerializationHelpers

diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab.Test/UnitTest1.cs
--- a/Implab.Test/UnitTest1.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab.Test/UnitTest1.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics;
 using System.Threading;
 using Xunit;
 
@@ -9,9 +10,20 @@
         [Fact]
         public void Test1()
         {
-            using(var cts = new CancellationTokenSource(1000)) {
-                PromiseHelper.Sleep(10000, cts.Token).Join();
-            }
+            var listener = new TextWriterTraceListener(Console.Out);
+            var source = new TraceSource("Custom",SourceLevels.ActivityTracing);
+
+            source.Listeners.Add(listener);
+
+            Trace.Listeners.Add(listener);
+            Trace.WriteLine("Hello!");
+            Trace.CorrelationManager.StartLogicalOperation();
+            Trace.WriteLine("Inner");
+            foreach(var x in Trace.CorrelationManager.LogicalOperationStack)
+                Trace.WriteLine($"-{x}");
+            source.TraceEvent(TraceEventType.Information, 1, "source event");
+            source.TraceData(TraceEventType.Start, 1, DateTime.Now);
+            Trace.CorrelationManager.StopLogicalOperation();
         }
     }
 }
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Automaton/DFATable.cs
--- a/Implab/Automaton/DFATable.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Automaton/DFATable.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -20,7 +20,7 @@
         #region IDFADefinition implementation
 
         public bool IsFinalState(int s) {
-            Safe.ArgumentInRange(s, 0, m_stateCount, "s");
+            Safe.ArgumentInRange(s >= 0 && s < m_stateCount, nameof(s));
 
             return m_finalStates.Contains(s);
         }
@@ -46,7 +46,7 @@
         #endregion
 
         public void SetInitialState(int s) {
-            Safe.ArgumentAssert(s >= 0, "s");
+            Safe.ArgumentInRange(s >= 0, nameof(s));
             m_stateCount = Math.Max(m_stateCount, s + 1);
             m_initialState = s;
         }
@@ -57,9 +57,9 @@
         }
 
         public void Add(AutomatonTransition item) {
-            Safe.ArgumentAssert(item.s1 >= 0, "item");
-            Safe.ArgumentAssert(item.s2 >= 0, "item");
-            Safe.ArgumentAssert(item.edge >= 0, "item");
+            Safe.ArgumentAssert(item.s1 >= 0, nameof(item));
+            Safe.ArgumentAssert(item.s2 >= 0, nameof(item));
+            Safe.ArgumentAssert(item.edge >= 0, nameof(item));
 
             m_stateCount = Math.Max(m_stateCount, Math.Max(item.s1, item.s2) + 1);
             m_symbolCount = Math.Max(m_symbolCount, item.edge + 1);
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Components/ExecutionState.cs
--- a/Implab/Components/ExecutionState.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Components/ExecutionState.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -15,6 +15,8 @@
 
         Stopping,
 
+        Stopped,
+
         Failed,
 
         Disposed,
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Components/IInitializable.cs
--- a/Implab/Components/IInitializable.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Components/IInitializable.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -11,9 +11,16 @@
         /// Completes initialization.
         /// </summary>
         /// <remarks>
+        /// <para>
         /// Normally virtual methods shouldn't be called from the constructor, due to the incomplete object state, but
         /// they can be called from this method. This method is also usefull when we constructing a complex grpah
         /// of components where cyclic references may take place.
+        /// </para>
+        /// <para>
+        /// In asyncronous patterns <see cref="Initialize()"/> can be called
+        /// to start initialization and the <see cref="IRunnable.Completion"/>
+        /// property can be used to track operation completion.
+        /// </para>
         /// </remarks>
         void Initialize();
     }
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Components/IRunnable.cs
--- a/Implab/Components/IRunnable.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Components/IRunnable.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -6,23 +6,53 @@
     /// <summary>
     /// Interface for the component which performs a long running task.
     /// </summary>
-    public interface IRunnable : IDisposable {
+    /// <remarks>
+    /// The access to the runnable component should be sequential, the
+    /// componet should support asynchronous completion of the initiated
+    /// operation but operations itself must be initiated sequentially.
+    /// </remarks>
+    public interface IRunnable {
         /// <summary>
         /// Starts this instance
         /// </summary>
+        /// <remarks>
+        /// This operation is cancellable and it's expected to move to
+        /// the failed state or just ignore the cancellation request,
+        /// </remarks>
         void Start(CancellationToken ct);
 
         /// <summary>
-        /// Stops this instance and releases all resources, after the instance is stopped it is moved to Disposed state and can't be reused.
+        /// Stops this instance and releases all resources, after the
+        /// instance is stopped it is moved to Disposed state and
+        /// can't be reused.
         /// </summary>
+        /// <remarks>
+        /// If the componet was in the starting state the pending operation
+        /// will be requested to cancel. The stop operatin will be
+        /// performed only if the component in the running state.
+        /// </remarks>
         void Stop(CancellationToken ct);
 
-        Task<ExecutionState> Completion { get; }
+        /// <summary>
+        /// The result of the last started operation. This property reflects
+        /// only the result of the last started operation and therefore should
+        /// change only if a new operation is initiated.
+        /// </summary>
+        Task Completion { get; }
 
+        /// <summary>
+        /// Current state of the componenet
+        /// </summary>
         ExecutionState State { get; }
 
+        /// <summary>
+        /// Event to monitor the state of the component.
+        /// </summary>
         event EventHandler<StateChangeEventArgs> StateChanged;
 
+        /// <summary>
+        /// The last error
+        /// </summary>
         Exception LastError { get; }
     }
 }
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Components/ObjectPool.cs
--- a/Implab/Components/ObjectPool.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Components/ObjectPool.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -26,7 +26,7 @@
         }
 
         protected ObjectPool(int size) {
-            Safe.ArgumentInRange(size,1,size,"size");
+            Safe.ArgumentInRange(size > 0, nameof(size));
 
             m_size = size;
         }
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Components/RunnableComponent.cs
--- a/Implab/Components/RunnableComponent.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Components/RunnableComponent.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -1,57 +1,273 @@
 using System;
+using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
 
-namespace Implab.Components
-{
-    public class RunnableComponent : IRunnable {
+namespace Implab.Components {
+    /// <summary>
+    /// Base class for implementing components which support start and stop operations,
+    /// such components may represent running services.
+    /// </summary>
+    /// <remarks>
+    /// This class provides a basic lifecycle from the creation to the
+    /// termination of the component.
+    /// </remarks>
+    public class RunnableComponent : IRunnable, IInitializable, IDisposable {
+
+        /// <summary>
+        /// This class bound <see cref="CancellationTokenSource"/> lifetime to the task,
+        /// when the task completes the associated token source will be disposed.
+        /// </summary>
+        class AsyncOperationDescriptor {
+
+            public static AsyncOperationDescriptor None { get; } = new AsyncOperationDescriptor();
+
+            readonly CancellationTokenSource m_cts;
+
+            bool m_done;
+
+            public CancellationToken Token {
+                get { return m_cts == null ? CancellationToken.None : m_cts.Token; }
+            }
+
+            public Task Task { get; private set; }
+
+            private AsyncOperationDescriptor(Task task, CancellationTokenSource cts) {
+                m_cts = cts;
+                Task = Chain(task);
+            }
+
+            private AsyncOperationDescriptor() {
+                Task = Task.CompletedTask;
+            }
 
+            public void Cancel() {
+                if (m_cts != null) {
+                    lock (m_cts) {
+                        if (!m_done)
+                            m_cts.Cancel();
+                    }
+                }
+            }
+
+            void Done() {
+                if (m_cts != null) {
+                    lock (m_cts) {
+                        m_done = true;
+                        m_cts.Dispose();
+                    }
+                } else {
+                    m_done = true;
+                }
+            }
+
+            async Task Chain(Task other) {
+                try {
+                    await other;
+                } finally {
+                    Done();
+                }
+            }
+
+            public static AsyncOperationDescriptor Create(Func<CancellationToken, Task> factory, CancellationToken ct) {
+                var cts = ct.CanBeCanceled ?
+                    CancellationTokenSource.CreateLinkedTokenSource(ct) :
+                    new CancellationTokenSource();
+
+                return new AsyncOperationDescriptor(factory(cts.Token), cts);
+            }
+
+        }
+
+        // this lock is used to synchronize state flow of the component during
+        // completions or the operations.
         readonly object m_lock = new object();
 
-        CancellationTokenSource m_cts;
+        // current operation cookie, used to check wheather a call to
+        // MoveSuccess/MoveFailed method belongs to the current
+        // operation, if cookies didn't match ignore completion result.
+        object m_cookie;
 
-        public Task<ExecutionState> Completion {
-            get;
-            private set;
+        AsyncOperationDescriptor m_current = AsyncOperationDescriptor.None;
+
+        ExecutionState m_state;
+
+
+        protected RunnableComponent(bool initialized) {
+            State = initialized ? ExecutionState.Ready : ExecutionState.Created;
         }
 
-        public ExecutionState State => throw new NotImplementedException();
+        public Task Completion {
+            get { return m_current.Task; }
+        }
 
-        public Exception LastError => throw new NotImplementedException();
+        public ExecutionState State {
+            get { return m_state; }
+            private set {
+                if (m_state != value) {
+                    m_state = value;
+                    StateChanged.DispatchEvent(this, new StateChangeEventArgs {
+                        State = value,
+                        LastError = LastError
+                    });
+                }
+            }
+        }
+
+        public Exception LastError { get; private set; }
 
         public event EventHandler<StateChangeEventArgs> StateChanged;
 
+        /// <summary>
+        /// Releases all resources used by the current component regardless of its
+        /// execution state.
+        /// </summary>
+        /// <remarks>
+        /// Calling to this method may result unexpedted results if the component
+        /// isn't in the stopped state. Call this method after the component is
+        /// stopped if needed or if the component is in the failed state.
+        /// </remarks>
         public void Dispose() {
-            lock(m_lock) {
+            bool dispose = false;
+            if (dispose) {
                 Dispose(true);
                 GC.SuppressFinalize(this);
             }
         }
 
+        ~RunnableComponent() {
+            Dispose(false);
+        }
+
+        /// <summary>
+        /// Releases all resources used by the current component regardless of its
+        /// execution state.
+        /// </summary>
+        /// <param name="disposing">Indicates that the component is disposed
+        /// during a normal disposing or during GC.</param>
         protected virtual void Dispose(bool disposing) {
-            if (disposing) {
-                Safe.Dispose(m_cts);
-            }
+        }
+
+        public void Initialize() {
+            var cookie = new object();
+            if (MoveInitialize(cookie))
+                ScheduleTask(InitializeInternalAsync, CancellationToken.None, cookie);
+        }
+
+        /// <summary>
+        /// This method is used for initialization during a component creation.
+        /// </summary>
+        /// <param name="ct">A cancellation token for this operation</param>
+        /// <remarks>
+        /// This method should be used for short and mostly syncronous operations,
+        /// other operations which require time to run shoud be placed in
+        /// <see cref="StartInternal(CancellationToken)"/> method.
+        /// </remarks>
+        protected virtual Task InitializeInternalAsync(CancellationToken ct) {
+            return Task.CompletedTask;
         }
 
         public void Start(CancellationToken ct) {
-            lock(m_lock) {
-                switch (State)
-                {
-                    
-                    default:
-                        throw new InvalidOperationException();
+            var cookie = new object();
+            if (MoveStart(cookie))
+                ScheduleTask(StartInternal, ct, cookie);
+        }
+
+        protected virtual Task StartInternal(CancellationToken ct) {
+            return Task.CompletedTask;
+        }
+
+        public void Stop(CancellationToken ct) {
+            var cookie = new object();
+            if (MoveStop(cookie))
+                ScheduleTask(StopAsync, ct, cookie);
+        }
+
+        async Task StopAsync(CancellationToken ct) {
+            m_current.Cancel();
+            await Completion;
+
+            ct.ThrowIfCancellationRequested();
+
+            await StopInternalAsync(ct);
+        }
+
+        protected virtual Task StopInternalAsync(CancellationToken ct) {
+            return Task.CompletedTask;
+        }
+
+
+        #region state management
+
+        bool MoveInitialize(object cookie) {
+            lock (m_lock) {
+                if (State != ExecutionState.Created)
+                    return false;
+                State = ExecutionState.Initializing;
+                m_cookie = cookie;
+                return true;
+            }
+        }
+
+        bool MoveStart(object cookie) {
+            lock (m_lock) {
+                if (State != ExecutionState.Ready)
+                    return false;
+                State = ExecutionState.Starting;
+                m_cookie = cookie;
+                return true;
+            }
+        }
+
+        bool MoveStop(object cookie) {
+            lock (m_lock) {
+                if (State != ExecutionState.Starting && State != ExecutionState.Running)
+                    return false;
+                State = ExecutionState.Stopping;
+                m_cookie = cookie;
+                return true;
+            }
+        }
+
+        void MoveSuccess(object cookie) {
+            lock (m_lock) {
+                if (m_cookie != cookie)
+                    return;
+                switch (State) {
+                    case ExecutionState.Initializing:
+                        State = ExecutionState.Ready;
+                        break;
+                    case ExecutionState.Starting:
+                        State = ExecutionState.Running;
+                        break;
+                    case ExecutionState.Stopping:
+                        State = ExecutionState.Stopped;
+                        break;
                 }
             }
         }
 
-        public void Stop(CancellationToken ct) {
-            throw new NotImplementedException();
+        void MoveFailed(Exception err, object cookie) {
+            lock (m_lock) {
+                if (m_cookie != cookie)
+                    return;
+                LastError = err;
+                State = ExecutionState.Failed;
+            }
         }
 
-        protected virtual Task StartImpl(CancellationToken ct) {
+
 
-            return Task.CompletedTask;
+        protected async void ScheduleTask(Func<CancellationToken, Task> next, CancellationToken ct, object cookie) {
+            try {
+                m_current = AsyncOperationDescriptor.Create(next, ct);
+                await m_current.Task;
+                MoveSuccess(cookie);
+            } catch (Exception e) {
+                MoveFailed(e, cookie);
+            }
         }
+
+        #endregion
     }
 }
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Deferred.cs
--- a/Implab/Deferred.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Deferred.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Threading.Tasks;
 
 namespace Implab {
     /// <summary>
@@ -49,5 +50,15 @@
             }
         }
 
+        public virtual void Resolve(Task thenable) {
+            if (thenable == null)
+                Reject(new Exception("The promise or task are expected"));
+            try {
+                thenable.Then(this);
+            } catch(Exception err) {
+                Reject(err);
+            }
+        }
+
     }
 }
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Deferred`1.cs
--- a/Implab/Deferred`1.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Deferred`1.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Threading.Tasks;
 
 namespace Implab {
     public class Deferred<T> : IResolvable<T> {
@@ -45,5 +46,16 @@
                 Reject(err);
             }
         }
+
+        public virtual void Resolve(Task<T> thenable) {
+            if (thenable == null)
+                Reject(new Exception("The promise or task are expected"));
+            
+            try {
+                thenable.Then(this);
+            } catch (Exception err) {
+                Reject(err);
+            }
+        }
     }
 }
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Formats/Json/JsonStringScanner.cs
--- a/Implab/Formats/Json/JsonStringScanner.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Formats/Json/JsonStringScanner.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -43,11 +43,8 @@
 
         public static JsonStringScanner Create(string data, int offset, int length) {
             Safe.ArgumentNotNull(data, nameof(data));
-            Safe.ArgumentGreaterThan(offset, 0, nameof(offset));
-            Safe.ArgumentGreaterThan(length, 0, nameof(length));
-
-            if (offset + length > data.Length)
-                throw new ArgumentOutOfRangeException("Specified offset and length are out of the string bounds");
+            Safe.ArgumentInRange(offset >= 0 && offset < data.Length , nameof(offset));
+            Safe.ArgumentInRange(length >= 0 && offset + length <= data.Length, nameof(length));
 
             if (length <= _defaultBuffer) {
                 var buffer = new char[length];
@@ -63,11 +60,8 @@
 
         public static JsonStringScanner Create(char[] data, int offset, int length) {
             Safe.ArgumentNotNull(data, nameof(data));
-            Safe.ArgumentGreaterThan(offset, 0, nameof(offset));
-            Safe.ArgumentGreaterThan(length, 0, nameof(length));
-
-            if (offset + length > data.Length)
-                throw new ArgumentOutOfRangeException("Specified offset and length are out of the array bounds");
+            Safe.ArgumentInRange(offset >= 0 && offset < data.Length , nameof(offset));
+            Safe.ArgumentInRange(length >= 0 && offset + length <= data.Length, nameof(length));
 
             return new JsonStringScanner(null, data, offset, offset + length, offset + length);
 
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Messaging/IConsumer.cs
--- a/Implab/Messaging/IConsumer.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Messaging/IConsumer.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -3,7 +3,9 @@
 
 namespace Implab.Messaging {
     public interface IConsumer<T> {
-        Task<T> Receive(CancellationToken ct);
+        T Receive(CancellationToken ct);
+
+        Task<T> ReceiveAsync(CancellationToken ct);
 
         bool TryReceive(out T message);
     }
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Messaging/IProducer.cs
--- a/Implab/Messaging/IProducer.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Messaging/IProducer.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -4,8 +4,12 @@
 
 namespace Implab.Messaging {
     public interface IProducer<T> {
+        void PostMessage(T message, CancellationToken ct);
+
         Task PostMessageAsync(T message, CancellationToken ct);
 
+        void PostMessages(IEnumerable<T> messages, CancellationToken ct);
+
         Task PostMessagesAsync(IEnumerable<T> messages, CancellationToken ct);
     }
 }
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Messaging/ISession.cs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/Messaging/ISession.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -0,0 +1,14 @@
+namespace Implab.Messaging {
+    public interface ISession {
+        /// <summary>
+        /// Starts message consumers, call this method after all adapters are ready
+        /// </summary>
+        void Start();
+
+        /// <summary>
+        /// Stops message consumers
+        /// </summary>
+        void Stop();
+
+    }
+}
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Parallels/BlockingQueue.cs
--- a/Implab/Parallels/BlockingQueue.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Parallels/BlockingQueue.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -54,7 +54,7 @@
         }
 
         public T[] GetRange(int max, int timeout) {
-            Safe.ArgumentInRange(max, 1, Int32.MaxValue, "max");
+            Safe.ArgumentInRange(max > 0 , nameof(max));
 
             var buffer = new T[max];
             int actual;
@@ -83,7 +83,7 @@
         }
 
         public T[] GetRange(int max) {
-            Safe.ArgumentInRange(max, 1, Int32.MaxValue, "max");
+            Safe.ArgumentInRange(max > 0, nameof(max));
 
             var buffer = new T[max];
             int actual;
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Safe.cs
--- a/Implab/Safe.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Safe.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.Collections;
 using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
 
 #if NET_4_5
 using System.Threading.Tasks;
@@ -48,14 +49,14 @@
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal static void ArgumentGreaterThan(int value, int min, string paramName) {
+        internal static void ArgumentGreaterEqThan(int value, int min, string paramName) {
             if (value < min)
                 throw new ArgumentOutOfRangeException(paramName);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ArgumentInRange(int value, int min, int max, string paramName) {
-            if (value < min || value > max)
+        public static void ArgumentInRange(bool condition, string paramName) {
+            if (!condition)
                 throw new ArgumentOutOfRangeException(paramName);
         }
 
@@ -144,6 +145,12 @@
         public static void NoWait(IPromise promise) {
         }
 
+        public static void NoWait(Task promise) {
+        }
+
+        public static void NoWait<T>(Task<T> promise) {
+        }
+
         [DebuggerStepThrough]
         public static IPromise<T> Run<T>(Func<IPromise<T>> action) {
             ArgumentNotNull(action, "action");
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/TaskHelpers.cs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/TaskHelpers.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -0,0 +1,70 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Implab {
+    public static class TaskHelpers {
+
+        public static async Task Then(this Task that, Action fulfilled, Action<Exception> rejected) {
+            Safe.ArgumentNotNull(that, nameof(that));
+            if (rejected != null) {
+                try {
+                    await that;
+                } catch (Exception e) {
+                    rejected(e);
+                    return;
+                }
+            } else {
+                await that;
+            }
+
+            if (fulfilled != null)
+                fulfilled();
+        }
+
+        public static async Task Then(this Task that, Action fulfilled) {
+            Safe.ArgumentNotNull(that, nameof(that));
+            await that;
+            if (fulfilled != null)
+                fulfilled();
+        }
+
+        public static async Task Then(this Task that, Func<Task> fulfilled) {
+            Safe.ArgumentNotNull(that, nameof(that));
+            await that;
+            if (fulfilled != null)
+                await fulfilled();
+        }
+
+        public static async Task Finally(this Task that, Action handler) {
+            Safe.ArgumentNotNull(that, nameof(that));
+            try {
+                await that;
+            } finally {
+                if (handler != null)
+                    handler();
+            }
+        }
+
+        public static async void Then(this Task that, IResolvable next) {
+            try {
+                await that;
+            } catch (Exception e) {
+                next.Reject(e);
+                return;
+            }
+            next.Resolve();
+        }
+
+        public static async void Then<T>(this Task<T> that, IResolvable<T> next) {
+            T result;
+            try {
+                result = await that;
+            } catch (Exception e) {
+                next.Reject(e);
+                return;
+            }
+            next.Resolve(result);
+        }
+
+    }
+}
\ No newline at end of file
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Xml/JsonXmlReader.cs
--- a/Implab/Xml/JsonXmlReader.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Xml/JsonXmlReader.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -163,7 +163,7 @@
         }
         
         public override string GetAttribute(int i) {
-            Safe.ArgumentInRange(i, 0, AttributeCount - 1, nameof(i));
+            Safe.ArgumentInRange(i >= 0 && i < AttributeCount, nameof(i));
             return m_attributes[i].Value;
         }
 
diff -r 9f63dade3a40 -r 7c7e9ad6fe4a Implab/Xml/SerializationHelpers.cs
--- a/Implab/Xml/SerializationHelpers.cs	Thu Feb 01 02:43:35 2018 +0300
+++ b/Implab/Xml/SerializationHelpers.cs	Sun Feb 11 00:49:51 2018 +0300
@@ -38,6 +38,20 @@
                 SerializersPool<T>.Instance.Serialize(writer, obj);
         }
 
+        public static void SerializeToElementChild<T>(XmlElement element, T obj) {
+            using(var writer = element.CreateNavigator().AppendChild())
+                SerializersPool<T>.Instance.Serialize(writer, obj);
+        }
+
+        public static T Deserialize<T>(XmlReader reader) {
+            return SerializersPool<T>.Instance.Deserialize(reader);
+        }
+
+        public static T DeserializeFromFile<T>(string file) {
+            using(var reader = XmlReader.Create(File.OpenText(file)))
+                return Deserialize<T>(reader);
+        }
+
         public static T DeserializeFromString<T>(string data) {
             return SerializersPool<T>.Instance.DeserializeFromString(data);
         }