1 files changed, 117 insertions, 0 deletions
diff --git a/Xamarin.Forms.Core/Ticker.cs b/Xamarin.Forms.Core/Ticker.cs
new file mode 100644
index 00000000..ed828f8a
--- /dev/null
+++ b/Xamarin.Forms.Core/Ticker.cs
@@ -0,0 +1,117 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading;
+
+namespace Xamarin.Forms
+{
+	internal class Ticker
+	{
+		static Ticker s_ticker;
+		readonly Stopwatch _stopwatch;
+		readonly SynchronizationContext _sync;
+		readonly List<Tuple<int, Func<long, bool>>> _timeouts;
+
+		readonly ITimer _timer;
+		int _count;
+		bool _enabled;
+
+		internal Ticker()
+		{
+			_sync = SynchronizationContext.Current;
+			_count = 0;
+			_timer = Device.PlatformServices.CreateTimer(HandleElapsed, null, Timeout.Infinite, Timeout.Infinite);
+			_timeouts = new List<Tuple<int, Func<long, bool>>>();
+
+			_stopwatch = new Stopwatch();
+		}
+
+		public static Ticker Default
+		{
+			internal set { s_ticker = value; }
+			get { return s_ticker ?? (s_ticker = new Ticker()); }
+		}
+
+		public virtual int Insert(Func<long, bool> timeout)
+		{
+			_count++;
+			_timeouts.Add(new Tuple<int, Func<long, bool>>(_count, timeout));
+
+			if (!_enabled)
+			{
+				_enabled = true;
+				Enable();
+			}
+
+			return _count;
+		}
+
+		public virtual void Remove(int handle)
+		{
+			Device.BeginInvokeOnMainThread(() =>
+			{
+				_timeouts.RemoveAll(t => t.Item1 == handle);
+
+				if (!_timeouts.Any())
+				{
+					_enabled = false;
+					Disable();
+				}
+			});
+		}
+
+		protected virtual void DisableTimer()
+		{
+			_timer.Change(Timeout.Infinite, Timeout.Infinite);
+		}
+
+		protected virtual void EnableTimer()
+		{
+			_timer.Change(16, 16);
+		}
+
+		protected void SendSignals(int timestep = -1)
+		{
+			long step = timestep >= 0 ? timestep : _stopwatch.ElapsedMilliseconds;
+			_stopwatch.Reset();
+			_stopwatch.Start();
+
+			var localCopy = new List<Tuple<int, Func<long, bool>>>(_timeouts);
+			foreach (Tuple<int, Func<long, bool>> timeout in localCopy)
+			{
+				bool remove = !timeout.Item2(step);
+				if (remove)
+					_timeouts.RemoveAll(t => t.Item1 == timeout.Item1);
+			}
+
+			if (!_timeouts.Any())
+			{
+				_enabled = false;
+				Disable();
+			}
+		}
+
+		void Disable()
+		{
+			_stopwatch.Reset();
+			DisableTimer();
+		}
+
+		void Enable()
+		{
+			_stopwatch.Start();
+			EnableTimer();
+		}
+
+		void HandleElapsed(object state)
+		{
+			if (_timeouts.Count > 0)
+			{
+				_sync.Post(o => SendSignals(), null);
+				_stopwatch.Reset();
+				_stopwatch.Start();
+			}
+		}
+	}
+}
+\ No newline at end of file