Moved the checkForTimeAdjustment() method in the generic time source behind the WaitOne() call because that's the most likely point for a date/time adjustment will have occurred at; WindowsTimeSource now exists on the XBox 360 as well, but will throw in its constructor and report Available as false (this simplifies things in other places); Scheduler class is fully working and 100% testable with simulated time (instead of waiting for scheduled notifications to be delivered in real time, which would make testing slow); added unit tests for Scheduler class and reached 100% coverage

git-svn-id: file:///srv/devel/repo-conversion/nusu@145 d2e56fa2-650e-0410-a79f-9358c0239efd

Source/Scheduling/GenericTimeSource.cs

@@ -87,12 +87,18 @@ namespace Nuclex.Support.Scheduling {
     ///   True if the WaitHandle was signalled, false if the timeout was reached
     /// </returns>
     public virtual bool WaitOne(AutoResetEvent waitHandle, long ticks) {
-      checkForTimeAdjustment();
 
       // Force a timeout at least each second so the caller can check the system time
       // since we're not able to provide the DateTimeAdjusted notification
       int milliseconds = (int)(ticks / TicksPerMillisecond);
-      return waitHandle.WaitOne(Math.Min(1000, milliseconds), false);
+      bool signalled = waitHandle.WaitOne(Math.Min(1000, milliseconds), false);
+
+      // See whether the system date/time have been adjusted while we were asleep.
+      checkForTimeAdjustment();
+
+      // Now tell the caller whether his even was signalled
+      return signalled;
+
     }
 
     /// <summary>Current system time in UTC format</summary>

Source/Scheduling/Scheduler.Test.cs

@@ -29,14 +29,175 @@ using Microsoft.Win32;
 
 using NUnit.Framework;
 
-#if false
-
 namespace Nuclex.Support.Scheduling {
 
   /// <summary>Unit Test for the scheduler</summary>
   [TestFixture]
   public class SchedulerTest {
 
+    #region class MockTimeSource
+
+    /// <summary>Mocked time source</summary>
+    private class MockTimeSource : ITimeSource {
+
+      /// <summary>Called when the system date/time are adjusted</summary>
+      public event EventHandler DateTimeAdjusted;
+
+      /// <summary>Initializes a new mocked time source</summary>
+      /// <param name="utcStartTime">Start time in UTC format</param>
+      public MockTimeSource(DateTime utcStartTime) {
+        this.currentTime = utcStartTime;
+      }
+
+      /// <summary>Waits for an AutoResetEvent to become signalled</summary>
+      /// <param name="waitHandle">WaitHandle the method will wait for</param>
+      /// <param name="ticks">Number of ticks to wait</param>
+      /// <returns>
+      ///   True if the WaitHandle was signalled, false if the timeout was reached
+      ///   or the time source thinks its time to recheck the system date/time.
+      /// </returns>
+      public bool WaitOne(AutoResetEvent waitHandle, long ticks) {
+        long currentTicks;
+        long eventDueTicks;
+        lock(this) {
+          this.autoResetEvent = waitHandle;
+          this.eventDueTicks += ticks;
+
+          currentTicks = this.currentTicks;
+          eventDueTicks = this.eventDueTicks;
+        }
+
+        // If we need to wait, use the wait handle. We do not use the wait handle's
+        // return value (or even its timeout) because we might trigger it ourselves
+        // to simulate the passing of time.
+        if(eventDueTicks > 0) {
+          this.autoResetEvent = waitHandle;
+          waitHandle.WaitOne();
+          this.autoResetEvent = null;
+        }
+
+        // Do not use the cached values here -- we might have used the WaitHandle and
+        // the simulation time could have been advanced while we were waiting.
+        lock(this) {
+          return (this.eventDueTicks > 0); // True = signalled, false = timed out
+        }
+      }
+
+      /// <summary>Current system time in UTC format</summary>
+      public DateTime CurrentUtcTime {
+        get { lock(this) { return this.currentTime; } }
+      }
+
+      /// <summary>How long the time source has been running</summary>
+      public long Ticks {
+        get {
+          lock(this) {
+            this.eventDueTicks = 0;
+            return this.currentTicks;
+          }
+        }
+      }
+
+      /// <summary>Advances the time of the time source</summary>
+      /// <param name="timeSpan">
+      ///   Time span by which to advance the time source's time
+      /// </param>
+      public void AdvanceTime(TimeSpan timeSpan) {
+        lock(this) {
+          this.currentTicks += timeSpan.Ticks;
+          this.currentTime += timeSpan;
+
+          // Problem: The Scheduler has just calculated the remaining ticks until
+          //          notification occurs. Next, another thread advances simulation time
+          //          and then the scheduler calls this. It will wait, even though
+          //          the simultion time has progressed.
+          // To compensate this, we track the remaining time until the event is due
+          // and allow for a negative time budget if AdvanceTime() is called after
+          // the scheduler has just queried the current tick count.
+          this.eventDueTicks -= timeSpan.Ticks;
+
+          if(this.eventDueTicks <= 0) {
+            AutoResetEvent copy = this.autoResetEvent;
+            if(copy != null) {
+              copy.Set();
+            }
+          }
+        }
+      }
+
+      /// <summary>Manually triggers the date time adjusted event</summary>
+      /// <param name="newUtcTime">New simulation time to jump to</param>
+      public void AdjustTime(DateTime newUtcTime) {
+        lock(this) {
+          this.currentTime = newUtcTime;
+        }
+        EventHandler copy = DateTimeAdjusted;
+        if(copy != null) {
+          copy(this, EventArgs.Empty);
+        }
+      }
+
+      /// <summary>Auto reset event the time source is currently waiting on</summary>
+      private volatile AutoResetEvent autoResetEvent;
+      /// <summary>Ticks at which the auto reset event will be due</summary>
+      private long eventDueTicks;
+      /// <summary>Current time source tick counter</summary>
+      private long currentTicks;
+      /// <summary>Current system time and date</summary>
+      private DateTime currentTime;
+
+    }
+
+    #endregion // class MockTimeSource
+
+    #region class TestSubscriber
+
+    /// <summary>Subscriber used to test the scheduler notifications</summary>
+    private class TestSubscriber : IDisposable {
+
+      /// <summary>Initializes a new test subscriber</summary>
+      public TestSubscriber() {
+        this.waitHandle = new AutoResetEvent(false);
+      }
+
+      /// <summary>Immediately releases all resources owned by the instance</summary>
+      public void Dispose() {
+        if(this.waitHandle != null) {
+          this.waitHandle.Close();
+          this.waitHandle = null;
+        }
+      }
+
+      /// <summary>Callback method that can be subscribed to the scheduler</summary>
+      /// <param name="state">Not used</param>
+      public void Callback(object state) {
+        Interlocked.Increment(ref this.callbackCount);
+        this.waitHandle.Set();
+      }
+
+      /// <summary>Blocks ther caller until the callback is invoked</summary>
+      /// <param name="milliseconds">
+      ///   Maximum number of milliseconds to wait for the callback
+      /// </param>
+      /// <returns>True if the callback was invoked, false if the call timed out</returns>
+      public bool WaitForCallback(int milliseconds) {
+        return this.waitHandle.WaitOne(milliseconds);
+      }
+
+      /// <summary>Number of times the callback has been invoked</summary>
+      public int CallbackCount {
+        get { return Thread.VolatileRead(ref this.callbackCount); }
+      }
+
+      /// <summary>Callback invocation count</summary>
+      private int callbackCount;
+      /// <summary>WaitHandle used to wait for the callback</summary>
+      private AutoResetEvent waitHandle;
+
+    }
+
+    #endregion // class TestSubscriber
+
     /// <summary>
     ///   Test whether the Scheduler can explicitely create a windows time source
     /// </summary>
@@ -96,10 +257,200 @@ namespace Nuclex.Support.Scheduling {
       using(Scheduler scheduler = new Scheduler()) { }
     }
 
+    /// <summary>
+    ///   Verifies that the default constructor of the scheduler is working
+    /// </summary>
+    [Test]
+    public void TestThrowOnNotifyAtWithUnspecifiedDateTimeKind() {
+      using(TestSubscriber subscriber = new TestSubscriber()) {
+        using(Scheduler scheduler = new Scheduler()) {
+          Assert.Throws<ArgumentException>(
+            delegate() {
+              scheduler.NotifyAt(new DateTime(2000, 1, 1), subscriber.Callback);
+            }
+          );
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Tests whether the NotifyAt() method invokes the callback at the right time
+    /// </summary>
+    [Test]
+    public void TestNotifyAt() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber = new TestSubscriber()) {
+        using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+          scheduler.NotifyAt(makeUtc(new DateTime(2010, 1, 2)), subscriber.Callback);
+
+          mockTimeSource.AdvanceTime(TimeSpan.FromDays(1));
+
+          Assert.IsTrue(subscriber.WaitForCallback(1000));
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Verifies that a notification at an absolute time is processed correctly
+    ///   if a time synchronization occurs during the wait.
+    /// </summary>
+    [Test]
+    public void TestNotifyAtWithDateTimeAdjustment() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber = new TestSubscriber()) {
+        using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+          scheduler.NotifyAt(makeUtc(new DateTime(2010, 1, 2)), subscriber.Callback);
+
+          // Let 12 hours pass, after that, we simulate a time synchronization
+          // that puts the system 12 hours ahead of the original time.
+          mockTimeSource.AdvanceTime(TimeSpan.FromHours(12));
+          mockTimeSource.AdjustTime(new DateTime(2010, 1, 2));
+
+          Assert.IsTrue(subscriber.WaitForCallback(1000));
+        }
+      }
+    }
+
+    /// <summary>Tests whether the scheduler's Cancel() method is working</summary>
+    [Test]
+    public void TestCancelNotification() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber1 = new TestSubscriber()) {
+        using(TestSubscriber subscriber2 = new TestSubscriber()) {
+          using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+            object handle = scheduler.NotifyIn(
+              TimeSpan.FromHours(24), subscriber1.Callback
+            );
+            scheduler.NotifyIn(TimeSpan.FromHours(36), subscriber2.Callback);
+
+            mockTimeSource.AdvanceTime(TimeSpan.FromHours(12));
+            scheduler.Cancel(handle);
+            mockTimeSource.AdvanceTime(TimeSpan.FromHours(24));
+
+            // Wait for the second subscriber to be notified. This is still a race
+            // condition (there's no guarantee the thread pool will run tasks in
+            // the order they were added), but it's the best we can do without
+            // relying on an ugly Thread.Sleep() in this test.
+            Assert.IsTrue(subscriber2.WaitForCallback(1000));
+            Assert.AreEqual(0, subscriber1.CallbackCount);
+          }
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Tests the scheduler with two notifications that are scheduled in inverse
+    ///   order of their due time.
+    /// </summary>
+    [Test]
+    public void TestInverseOrderNotification() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber1 = new TestSubscriber()) {
+        using(TestSubscriber subscriber2 = new TestSubscriber()) {
+          using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+            scheduler.NotifyIn(TimeSpan.FromHours(24), subscriber1.Callback);
+            scheduler.NotifyIn(TimeSpan.FromHours(12), subscriber2.Callback);
+
+            mockTimeSource.AdvanceTime(TimeSpan.FromHours(18));
+
+            Assert.IsTrue(subscriber2.WaitForCallback(1000));
+            Assert.AreEqual(0, subscriber1.CallbackCount);
+
+            mockTimeSource.AdvanceTime(TimeSpan.FromHours(18));
+
+            Assert.IsTrue(subscriber1.WaitForCallback(1000));
+          }
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Tests the scheduler with two notifications that are scheduled to
+    ///   occur at the exact same time
+    /// </summary>
+    [Test]
+    public void TestTwoNotificationsAtSameTime() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber1 = new TestSubscriber()) {
+        using(TestSubscriber subscriber2 = new TestSubscriber()) {
+          using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+            scheduler.NotifyIn(60000, subscriber1.Callback);
+            scheduler.NotifyIn(60000, subscriber2.Callback);
+
+            mockTimeSource.AdvanceTime(TimeSpan.FromMilliseconds(60000));
+
+            Assert.IsTrue(subscriber1.WaitForCallback(1000));
+            Assert.IsTrue(subscriber2.WaitForCallback(1000));
+          }
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Verifies that the scheduler's NotifyEach() method is working correctly
+    /// </summary>
+    [Test]
+    public void TestNotifyEachWithMilliseconds() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber = new TestSubscriber()) {
+        using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+          scheduler.NotifyEach(1000, 1000, subscriber.Callback);
+
+          mockTimeSource.AdvanceTime(TimeSpan.FromMilliseconds(4000));
+
+          // Wait for 4 invocations of the callback. We might not catch each trigger
+          // of the AutoResetEvent, but we know that it will be 4 at most. 
+          for(int invocation = 0; invocation < 4; ++invocation) {
+            Assert.IsTrue(subscriber.WaitForCallback(1000));
+
+            if(subscriber.CallbackCount == 4) {
+              break;
+            }
+          }
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Verifies that the scheduler's NotifyEach() method is working correctly
+    /// </summary>
+    [Test]
+    public void TestNotifyEachWithTimespan() {
+      MockTimeSource mockTimeSource = new MockTimeSource(new DateTime(2010, 1, 1));
+      using(TestSubscriber subscriber = new TestSubscriber()) {
+        using(Scheduler scheduler = new Scheduler(mockTimeSource)) {
+          scheduler.NotifyEach(
+            TimeSpan.FromHours(12), TimeSpan.FromHours(1), subscriber.Callback
+          );
+
+          mockTimeSource.AdvanceTime(TimeSpan.FromHours(14));
+
+          // Wait for 3 invocations of the callback. We might not catch each trigger
+          // of the AutoResetEvent, but we know that it will be 3 at most. 
+          for(int invocation = 0; invocation < 3; ++invocation) {
+            Assert.IsTrue(subscriber.WaitForCallback(1000));
+
+            if(subscriber.CallbackCount == 3) {
+              break;
+            }
+          }
+        }
+      }
+    }
+
+    /// <summary>Returns the provided date/time value as a utc time value</summary>
+    /// <param name="dateTime">Date/time value that will be returned as UTC</param>
+    /// <returns>The provided date/time value as UTC</returns>
+    /// <remarks>
+    ///   This doesn't convert the time, it just returns the exact same date and time
+    ///   but tags it as UTC by setting the DateTimeKind to UTC.
+    /// </remarks>
+    private static DateTime makeUtc(DateTime dateTime) {
+      return new DateTime(dateTime.Ticks, DateTimeKind.Utc);
+    }
+
   }
 
 } // namespace Nuclex.Support.Scheduling
 
-#endif
-
 #endif // UNITTEST

Source/Scheduling/Scheduler.cs

@@ -25,8 +25,6 @@ using System.Diagnostics;
 
 using Nuclex.Support.Collections;
 
-#if false
-
 namespace Nuclex.Support.Scheduling {
 
   /// <summary>Schedules actions for execution at a future point in time</summary>
@@ -77,7 +75,7 @@ namespace Nuclex.Support.Scheduling {
         long intervalTicks,
         long nextDueTicks,
         DateTime absoluteUtcTime,
-        Delegate callback
+        WaitCallback callback
       ) {
         this.IntervalTicks = intervalTicks;
         this.NextDueTicks = nextDueTicks;
@@ -100,7 +98,7 @@ namespace Nuclex.Support.Scheduling {
       /// </remarks>
       public DateTime AbsoluteUtcTime;
       /// <summary>Callback that will be invoked when the notification is due</summary>
-      public Delegate Callback;
+      public WaitCallback Callback;
       /// <summary>Whether the notification has been cancelled</summary>
       public bool Cancelled;
 
@@ -108,14 +106,44 @@ namespace Nuclex.Support.Scheduling {
 
     #endregion // class Notification
 
+    #region class NotificationComparer
+
+    /// <summary>Compares two notifications to each other</summary>
+    private class NotificationComparer : IComparer<Notification> {
+
+      /// <summary>The default instance of the notification comparer</summary>
+      public static readonly NotificationComparer Default = new NotificationComparer();
+
+      /// <summary>Compares two notifications to each other based on their time</summary>
+      /// <param name="left">Notification that will be compared on the left side</param>
+      /// <param name="right">Notification that will be comapred on the right side</param>
+      /// <returns>The relation of the two notification's times to each other</returns>
+      public int Compare(Notification left, Notification right) {
+        if(left.NextDueTicks > right.NextDueTicks) {
+          return -1;
+        } else if(left.NextDueTicks < right.NextDueTicks) {
+          return 1;
+        } else {
+          return 0;
+        }
+      }
+
+    #endregion // class NotificationComparer
+
+    }
+
     /// <summary>Initializes a new scheduler using the default time source</summary>
     public Scheduler() : this(DefaultTimeSource) { }
 
     /// <summary>Initializes a new scheduler using the specified time source</summary>
     /// <param name="timeSource">Source source the scheduler will use</param>
     public Scheduler(ITimeSource timeSource) {
+      this.dateTimeAdjustedDelegate = new EventHandler(dateTimeAdjusted);
+
       this.timeSource = timeSource;
-      this.notifications = new PriorityQueue<Notification>();
+      this.timeSource.DateTimeAdjusted += this.dateTimeAdjustedDelegate;
+
+      this.notifications = new PriorityQueue<Notification>(NotificationComparer.Default);
       this.notificationWaitEvent = new AutoResetEvent(false);
 
       this.timerThread = new Thread(new ThreadStart(runTimerThread));
@@ -138,6 +166,13 @@ namespace Nuclex.Support.Scheduling {
           this.timerThread.Join(2500), "Scheduler timer thread did not exit in time"
         );
 
+        // Unsubscribe from the time source to avoid surprise events during or
+        // after shutdown
+        if(this.timeSource != null) {
+          this.timeSource.DateTimeAdjusted -= this.dateTimeAdjustedDelegate;
+          this.timeSource = null;
+        }
+
         // Get rid of the notification wait event now that we've made sure that
         // the timer thread is down.
         this.notificationWaitEvent.Close();
@@ -145,7 +180,6 @@ namespace Nuclex.Support.Scheduling {
         // Help the GC a bit
         this.notificationWaitEvent = null;
         this.notifications = null;
-        this.timeSource = null;
 
         // Set to null so we don't attempt to end the thread again if Dispose() is
         // called multiple times.
@@ -168,7 +202,7 @@ namespace Nuclex.Support.Scheduling {
     ///   the notification. So if you need to be notified after a fixed time, use
     ///   the NotifyIn() method instead.
     /// </remarks>
-    public object NotifyAt(DateTime notificationTime, Delegate callback) {
+    public object NotifyAt(DateTime notificationTime, WaitCallback callback) {
       if(notificationTime.Kind == DateTimeKind.Unspecified) {
         throw new ArgumentException(
           "Notification time is neither UTC or local", "notificationTime"
@@ -176,7 +210,9 @@ namespace Nuclex.Support.Scheduling {
       }
 
       DateTime notificationTimeUtc = notificationTime.ToUniversalTime();
-      long remainingTicks = notificationTimeUtc.Ticks - DateTime.UtcNow.Ticks;
+      DateTime now = this.timeSource.CurrentUtcTime;
+
+      long remainingTicks = notificationTimeUtc.Ticks - now.Ticks;
       long nextDueTicks = this.timeSource.Ticks + remainingTicks;
 
       return scheduleNotification(
@@ -195,7 +231,7 @@ namespace Nuclex.Support.Scheduling {
     ///   Callback that will be invoked when the notification is due
     /// </param>
     /// <returns>A handle that can be used to cancel the notification</returns>
-    public object NotifyIn(TimeSpan delay, Delegate callback) {
+    public object NotifyIn(TimeSpan delay, WaitCallback callback) {
       return scheduleNotification(
         new Notification(
           0,
@@ -216,7 +252,7 @@ namespace Nuclex.Support.Scheduling {
     ///   Callback that will be invoked when the notification is due
     /// </param>
     /// <returns>A handle that can be used to cancel the notification</returns>
-    public object NotifyIn(int delayMilliseconds, Delegate callback) {
+    public object NotifyIn(int delayMilliseconds, WaitCallback callback) {
       return scheduleNotification(
         new Notification(
           0,
@@ -236,7 +272,7 @@ namespace Nuclex.Support.Scheduling {
     ///   Callback that will be invoked when the notification is due
     /// </param>
     /// <returns>A handle that can be used to cancel the notification</returns>
-    public object NotifyEach(TimeSpan delay, TimeSpan interval, Delegate callback) {
+    public object NotifyEach(TimeSpan delay, TimeSpan interval, WaitCallback callback) {
       return scheduleNotification(
         new Notification(
           interval.Ticks,
@@ -261,7 +297,7 @@ namespace Nuclex.Support.Scheduling {
     /// </param>
     /// <returns>A handle that can be used to cancel the notification</returns>
     public object NotifyEach(
-      int delayMilliseconds, int intervalMilliseconds, Delegate callback
+      int delayMilliseconds, int intervalMilliseconds, WaitCallback callback
     ) {
       return scheduleNotification(
         new Notification(
@@ -273,6 +309,17 @@ namespace Nuclex.Support.Scheduling {
       );
     }
 
+    /// <summary>Cancels a scheduled notification</summary>
+    /// <param name="notificationHandle">
+    ///   Handle of the notification that will be cancelled
+    /// </param>
+    public void Cancel(object notificationHandle) {
+      Notification notification = notificationHandle as Notification;
+      if(notification != null) {
+        notification.Cancelled = true;
+      }
+    }
+
     /// <summary>Returns the default time source for the scheduler</summary>
     public static ITimeSource DefaultTimeSource {
       get { return TimeSourceSingleton.Instance; }
@@ -297,11 +344,54 @@ namespace Nuclex.Support.Scheduling {
       return CreateTimeSource(WindowsTimeSource.Available);
     }
 
+    /// <summary>Called when the system date/time have been adjusted</summary>
+    /// <param name="sender">Time source which detected the adjustment</param>
+    /// <param name="arguments">Not used</param>
+    private void dateTimeAdjusted(object sender, EventArgs arguments) {
+      lock(this.timerThread) {
+        long currentTicks = this.timeSource.Ticks;
+        DateTime currentTime = this.timeSource.CurrentUtcTime;
+
+        PriorityQueue<Notification> updatedQueue = new PriorityQueue<Notification>(
+          NotificationComparer.Default
+        );
+
+        // Copy all notifications from the original queue to a new one, adjusting
+        // those with an absolute notification time along the way to a new due tick
+        while(this.notifications.Count > 0) {
+          Notification notification = this.notifications.Dequeue();
+          if(!notification.Cancelled) {
+
+            // If this notification has an absolute due time, adjust its due tick
+            if(notification.AbsoluteUtcTime != DateTime.MinValue) {
+
+              // Combining recurrent notifications with absolute time isn't allowed
+              Debug.Assert(notification.IntervalTicks == 0);
+
+              // Make the adjustment
+              long remainingTicks = (notification.AbsoluteUtcTime - currentTime).Ticks;
+              notification.NextDueTicks = currentTicks + remainingTicks;
+
+            }
+
+            // Notification processed, move it over to the next priority queue
+            updatedQueue.Enqueue(notification);
+
+          }
+        }
+
+        // Replace the working queue with the update queue
+        this.notifications = updatedQueue;
+      }
+
+      this.notificationWaitEvent.Set();
+    }
+
     /// <summary>Schedules a notification for processing by the timer thread</summary>
     /// <param name="notification">Notification that will be scheduled</param>
     /// <returns>The scheduled notification</returns>
     private object scheduleNotification(Notification notification) {
-      lock(this.notifications) {
+      lock(this.timerThread) {
         this.notifications.Enqueue(notification);
 
         // If this notification has become that next due notification, wake up
@@ -316,12 +406,15 @@ namespace Nuclex.Support.Scheduling {
 
     /// <summary>Executes the timer thread</summary>
     private void runTimerThread() {
+      Notification nextDueNotification;
+      lock(this.timerThread) {
+        nextDueNotification = getNextDueNotification();
+      }
 
+      // Keep processing notifications until we're told to quit
       for(; ; ) {
 
-        // Get the notification that is due next and wait for it. When no notifications
+        // Wait until the nextmost notification is due or something else wakes us up
-        // are queued, wait indefinitely until we're signalled
-        Notification nextDueNotification = getNextDueNotification();
         if(nextDueNotification == null) {
           this.notificationWaitEvent.WaitOne();
         } else {
@@ -334,17 +427,42 @@ namespace Nuclex.Support.Scheduling {
           break;
         }
 
-
+        // Process all notifications that are due by handing them over to the thread pool.
-        //if(nextDueNotification.AbsoluteUtcTime !=         
+        // The notification queue might have been updated while we were sleeping, so
-
+        // look for the notification that is due next again
+        long ticks = this.timeSource.Ticks;
+        lock(this.timerThread) {
+          for(; ; ) {
+            nextDueNotification = getNextDueNotification();
+            if(nextDueNotification == null) {
+              break;
             }
 
+            // If the next notification is more than a millisecond away, we've reached
+            // the end of the notifications we need to process.
+            long remainingTicks = (nextDueNotification.NextDueTicks - ticks);
+            if(remainingTicks >= TicksPerMillisecond) {
+              break;
+            }
+
+            if(!nextDueNotification.Cancelled) {
+              ThreadPool.QueueUserWorkItem(nextDueNotification.Callback);
+            }
+
+            this.notifications.Dequeue();
+            if(nextDueNotification.IntervalTicks != 0) {
+              nextDueNotification.NextDueTicks += nextDueNotification.IntervalTicks;
+              this.notifications.Enqueue(nextDueNotification);
+            }
+          } // for
+        } // lock
+
+      } // for
     }
 
     /// <summary>Retrieves the notification that is due next</summary>
     /// <returns>The notification that is due next</returns>
     private Notification getNextDueNotification() {
-      lock(this.notifications) {
       if(this.notifications.Count == 0) {
         return null;
       } else {
@@ -353,10 +471,10 @@ namespace Nuclex.Support.Scheduling {
           this.notifications.Dequeue();
           nextDueNotification = this.notifications.Peek();
         }
+
         return nextDueNotification;
       }
     }
-    }
 
     /// <summary>Time source used by the scheduler</summary>
     private ITimeSource timeSource;
@@ -370,8 +488,9 @@ namespace Nuclex.Support.Scheduling {
     /// <summary>Whether the timer thread should end</summary>
     private volatile bool endRequested;
 
+    /// <summary>Delegate for the dateTimeAdjusted() method</summary>
+    private EventHandler dateTimeAdjustedDelegate;
+
   }
 
 } // namespace Nuclex.Support.Scheduling
-
-#endif

Source/Scheduling/WindowsTimeSource.cs

@@ -18,13 +18,13 @@ License along with this library
 */
 #endregion
 
-#if !XBOX360
-
 using System;
 using System.Collections.Generic;
 using System.Threading;
 
+#if !XBOX360
 using Microsoft.Win32;
+#endif
 
 namespace Nuclex.Support.Scheduling {
 
@@ -38,16 +38,24 @@ namespace Nuclex.Support.Scheduling {
 
     /// <summary>Initializes a new Windows time source</summary>
     public WindowsTimeSource() {
+#if XBOX360
+      throw new InvalidOperationException(
+        "Windows time source is not available on the XBox 360"
+      );
+#else
       this.onDateTimeAdjustedDelegate = new EventHandler(OnDateTimeAdjusted);
       SystemEvents.TimeChanged += this.onDateTimeAdjustedDelegate;
+#endif
     }
 
     /// <summary>Immediately releases all resources owned by the instance</summary>
     public void Dispose() {
+#if !XBOX360
       if(this.onDateTimeAdjustedDelegate != null) {
         SystemEvents.TimeChanged -= this.onDateTimeAdjustedDelegate;
         this.onDateTimeAdjustedDelegate = null;
       }
+#endif
     }
 
     /// <summary>Waits for an AutoResetEvent to become signalled</summary>
@@ -57,7 +65,7 @@ namespace Nuclex.Support.Scheduling {
     ///   True if the WaitHandle was signalled, false if the timeout was reached
     /// </returns>
     public override bool WaitOne(AutoResetEvent waitHandle, long ticks) {
-      return waitHandle.WaitOne((int)(ticks / TicksPerMillisecond));
+      return waitHandle.WaitOne((int)(ticks / TicksPerMillisecond), false);
     }
 
     /// <summary>
@@ -73,5 +81,3 @@ namespace Nuclex.Support.Scheduling {
   }
 
 } // namespace Nuclex.Support.Scheduling
-
-#endif // !XBOX360