1 files changed, 113 insertions, 0 deletions
diff --git a/Rx.NET/System.Reactive.Core/Reactive/Internal/SystemClock.Default.cs b/Rx.NET/System.Reactive.Core/Reactive/Internal/SystemClock.Default.cs
new file mode 100644
index 0000000..b9c8167
--- /dev/null
+++ b/Rx.NET/System.Reactive.Core/Reactive/Internal/SystemClock.Default.cs
@@ -0,0 +1,113 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
+
+using System.ComponentModel;
+using System.Reactive.Concurrency;
+using System.Reactive.Disposables;
+
+namespace System.Reactive.PlatformServices
+{
+    /// <summary>
+    /// (Infrastructure) Provides access to the local system clock.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public class DefaultSystemClock : ISystemClock
+    {
+        /// <summary>
+        /// Gets the current time.
+        /// </summary>
+        public DateTimeOffset UtcNow
+        {
+            get { return DateTimeOffset.UtcNow; }
+        }
+    }
+
+    internal class DefaultSystemClockMonitor : PeriodicTimerSystemClockMonitor
+    {
+        private static readonly TimeSpan DEFAULT_PERIOD = TimeSpan.FromSeconds(1);
+
+        public DefaultSystemClockMonitor()
+            : base(DEFAULT_PERIOD)
+        {
+        }
+    }
+
+    /// <summary>
+    /// (Infrastructure) Monitors for system clock changes based on a periodic timer.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public class PeriodicTimerSystemClockMonitor : INotifySystemClockChanged
+    {
+        private readonly TimeSpan _period;
+        private readonly SerialDisposable _timer;
+
+        private DateTimeOffset _lastTime;
+        private EventHandler<SystemClockChangedEventArgs> _systemClockChanged;
+
+        private const int SYNC_MAXRETRIES = 100;
+        private const double SYNC_MAXDELTA = 10;
+        private const int MAXERROR = 100;
+
+        /// <summary>
+        /// Creates a new monitor for system clock changes with the specified polling frequency.
+        /// </summary>
+        /// <param name="period">Polling frequency for system clock changes.</param>
+        public PeriodicTimerSystemClockMonitor(TimeSpan period)
+        {
+            _period = period;
+            _timer = new SerialDisposable();
+        }
+
+        /// <summary>
+        /// Event that gets raised when a system clock change is detected.
+        /// </summary>
+        public event EventHandler<SystemClockChangedEventArgs> SystemClockChanged
+        {
+            add
+            {
+                NewTimer();
+
+                _systemClockChanged += value;
+            }
+
+            remove
+            {
+                _systemClockChanged -= value;
+
+                _timer.Disposable = Disposable.Empty;
+            }
+        }
+
+        private void NewTimer()
+        {
+            _timer.Disposable = Disposable.Empty;
+
+            var n = 0;
+            do
+            {
+                _lastTime = SystemClock.UtcNow;
+                _timer.Disposable = ConcurrencyAbstractionLayer.Current.StartPeriodicTimer(TimeChanged, _period);
+            } while (Math.Abs((SystemClock.UtcNow - _lastTime).TotalMilliseconds) > SYNC_MAXDELTA && ++n < SYNC_MAXRETRIES);
+
+            if (n >= SYNC_MAXRETRIES)
+                throw new InvalidOperationException(Strings_Core.FAILED_CLOCK_MONITORING);
+        }
+
+        private void TimeChanged()
+        {
+            var now = SystemClock.UtcNow;
+            var diff = now - (_lastTime + _period);
+            if (Math.Abs(diff.TotalMilliseconds) >= MAXERROR)
+            {
+                var scc = _systemClockChanged;
+                if (scc != null)
+                    scc(this, new SystemClockChangedEventArgs(_lastTime + _period, now));
+
+                NewTimer();
+            }
+            else
+            {
+                _lastTime = SystemClock.UtcNow;
+            }
+        }
+    }
+}