Add a polling component model

osu.Game/Online/PollingComponent.cs

@@ -0,0 +1,108 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Threading.Tasks;
+using osu.Framework.Graphics;
+using osu.Framework.Threading;
+
+namespace osu.Game.Online
+{
+    /// <summary>
+    /// A component which requires a constant polling process.
+    /// </summary>
+    public abstract class PollingComponent : Component
+    {
+        private double? lastTimePolled;
+
+        private ScheduledDelegate scheduledPoll;
+
+        private bool pollingActive;
+
+        private double timeBetweenPolls;
+
+        /// <summary>
+        /// The time that should be waited between polls.
+        /// </summary>
+        public double TimeBetweenPolls
+        {
+            get => timeBetweenPolls;
+            set
+            {
+                timeBetweenPolls = value;
+                scheduledPoll?.Cancel();
+                pollIfNecessary();
+            }
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+            pollIfNecessary();
+        }
+
+        private bool pollIfNecessary()
+        {
+            // we must be loaded so we have access to clock.
+            if (!IsLoaded) return false;
+
+            // there's already a poll process running.
+            if (pollingActive) return false;
+
+            // don't try polling if the time between polls hasn't been set.
+            if (timeBetweenPolls == 0) return false;
+
+            if (!lastTimePolled.HasValue)
+            {
+                doPoll();
+                return true;
+            }
+
+            if (Time.Current - lastTimePolled.Value > timeBetweenPolls)
+            {
+                doPoll();
+                return true;
+            }
+
+            // not ennough time has passed since the last poll. we do want to schedule a poll to happen, though.
+            scheduleNextPoll();
+            return false;
+        }
+
+        private void doPoll()
+        {
+            scheduledPoll = null;
+            pollingActive = true;
+            Poll().ContinueWith(_ => pollComplete());
+        }
+
+        /// <summary>
+        /// Perform the polling in this method. Call <see cref="pollComplete"/> when done.
+        /// </summary>
+        protected virtual Task Poll()
+        {
+            return Task.CompletedTask;
+        }
+
+        /// <summary>
+        /// Call when a poll operation has completed.
+        /// </summary>
+        private void pollComplete()
+        {
+            lastTimePolled = Time.Current;
+            pollingActive = false;
+
+            if (scheduledPoll == null)
+                scheduleNextPoll();
+        }
+
+        private void scheduleNextPoll()
+        {
+            scheduledPoll?.Cancel();
+
+            double lastPollDuration = lastTimePolled.HasValue ? Time.Current - lastTimePolled.Value : 0;
+
+            scheduledPoll = Scheduler.AddDelayed(doPoll, Math.Max(0, timeBetweenPolls - lastPollDuration));
+        }
+    }
+}