Rewrite TripleBuffer as a true lockless, flipping, triple buffer

osu.Framework.Tests/Graphics/TripleBufferTest.cs

@@ -40,196 +40,49 @@ public void TestSameBufferIsNotWrittenTwiceInRowNoContestation()
         {
             var tripleBuffer = createWithIDsMatchingIndices();
 
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(0));
+            int? lastWrite = null;
 
-            // buffer 0: waiting for read
-            // buffer 1: old
-            // buffer 2: old
-
-            using (var buffer = tripleBuffer.GetForRead())
-                Assert.That(buffer?.Object?.ID, Is.EqualTo(0));
-
-            // buffer 0: last read
-            // buffer 1: old
-            // buffer 2: old
-
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-            // buffer 0: last read
-            // buffer 1: waiting for read
-            // buffer 2: old
-
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(2));
-
-            // buffer 0: last read
-            // buffer 1: old
-            // buffer 2: waiting for read
-
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-            // buffer 0: last read
-            // buffer 1: waiting for read
-            // buffer 2: old
-
-            using (var buffer = tripleBuffer.GetForRead())
-                Assert.That(buffer?.Object?.ID, Is.EqualTo(1));
-
-            // buffer 0: old
-            // buffer 1: last read
-            // buffer 2: old
-        }
-
-        [Test]
-        public void TestSameBufferIsNotWrittenTwiceInRowContestation()
-        {
-            var tripleBuffer = createWithIDsMatchingIndices();
-
-            // Test with first write in use during second.
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(0));
-
-            // buffer 0: waiting for read
-            // buffer 1: old
-            // buffer 2: old
-
-            using (var read = tripleBuffer.GetForRead())
-            {
-                Assert.That(read?.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: reading
-                // buffer 1: old
-                // buffer 2: old
-
-                using (var write = tripleBuffer.GetForWrite())
-                    Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-                // buffer 0: reading
-                // buffer 1: waiting for read
-                // buffer 2: old
-
-                using (var write = tripleBuffer.GetForWrite())
-                    Assert.That(write.Object?.ID, Is.EqualTo(2));
-
-                // buffer 0: reading
-                // buffer 1: old
-                // buffer 2: waiting for read
-            }
-
-            using (var read = tripleBuffer.GetForRead())
+            for (int i = 0; i < 3; i++)
             {
-                Assert.That(read?.Object?.ID, Is.EqualTo(2));
-
-                // buffer 0: old
-                // buffer 1: old
-                // buffer 2: reading
-
-                using (var write = tripleBuffer.GetForWrite())
-                    Assert.That(write.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: waiting for read
-                // buffer 1: old
-                // buffer 2: reading
-
                 using (var write = tripleBuffer.GetForWrite())
-                    Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-                // buffer 0: old
-                // buffer 1: waiting for read
-                // buffer 2: reading
-
-                using (var write = tripleBuffer.GetForWrite())
-                    Assert.That(write.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: waiting for read
-                // buffer 1: old
-                // buffer 2: reading
-            }
+                {
+                    Assert.That(write.Object!.ID, Is.Not.EqualTo(lastWrite));
+                    lastWrite = write.Object!.ID;
+                }
 
-            using (var read = tripleBuffer.GetForRead())
-            {
-                Assert.That(read?.Object?.ID, Is.EqualTo(0));
-                // buffer 0: reading
-                // buffer 1: old
-                // buffer 2: old
+                using (var buffer = tripleBuffer.GetForRead())
+                    Assert.That(buffer!.Object!.ID, Is.EqualTo(lastWrite));
             }
         }
 
         [Test]
-        public void TestSameBufferIsNotWrittenTwiceInRowContestation2()
+        public void TestSameBufferIsNotWrittenTwiceInRowContestation()
         {
             var tripleBuffer = createWithIDsMatchingIndices();
 
-            using (var write = tripleBuffer.GetForWrite())
-                Assert.That(write.Object?.ID, Is.EqualTo(0));
-
-            // buffer 0: waiting for read
-            // buffer 1: old
-            // buffer 2: old
-
-            using (var read = tripleBuffer.GetForRead())
-            {
-                Assert.That(read?.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: reading
-                // buffer 1: old
-                // buffer 2: old
-
-                using (var write = tripleBuffer.GetForWrite())
-                {
-                    Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-                    // buffer 0: reading
-                    // buffer 1: writing
-                    // buffer 2: old
-                }
-            }
-
-            using (var read = tripleBuffer.GetForRead())
+            // Test with first write in use during second.
+            using (tripleBuffer.GetForWrite())
             {
-                Assert.That(read?.Object?.ID, Is.EqualTo(1));
-
-                // buffer 0: old
-                // buffer 1: reading
-                // buffer 2: old
             }
 
-            using (var write = tripleBuffer.GetForWrite())
-            {
-                Assert.That(write.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: writing
-                // buffer 1: last read
-                // buffer 2: old
-            }
+            int? lastRead = null;
+            int? lastWrite = null;
 
-            using (var read = tripleBuffer.GetForRead())
+            for (int i = 0; i < 3; i++)
             {
-                Assert.That(read?.Object?.ID, Is.EqualTo(0));
-
-                // buffer 0: reading
-                // buffer 1: old
-                // buffer 2: old
-
-                using (var write = tripleBuffer.GetForWrite())
+                using (var read = tripleBuffer.GetForRead())
                 {
-                    Assert.That(write.Object?.ID, Is.EqualTo(1));
-
-                    // buffer 0: reading
-                    // buffer 1: writing
-                    // buffer 2: old
-                }
-
-                using (var write = tripleBuffer.GetForWrite())
-                {
-                    Assert.That(write.Object?.ID, Is.EqualTo(2));
-
-                    // buffer 0: reading
-                    // buffer 1: waiting for read
-                    // buffer 2: writing
+                    Assert.That(read!.Object!.ID, Is.Not.EqualTo(lastRead));
+
+                    for (int j = 0; j < 3; j++)
+                    {
+                        using (var write = tripleBuffer.GetForWrite())
+                        {
+                            Assert.That(write.Object!.ID, Is.Not.EqualTo(lastWrite));
+                            Assert.That(write.Object!.ID, Is.Not.EqualTo(read.Object?.ID));
+                            lastWrite = write.Object!.ID;
+                        }
+                    }
                 }
             }
         }

osu.Framework.Tests/Visual/Graphics/TestSceneTripleBufferOccupancy.cs

@@ -0,0 +1,124 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+
+namespace osu.Framework.Tests.Visual.Graphics
+{
+    public partial class TestSceneTripleBufferOccupancy : FrameworkTestScene
+    {
+        private readonly CancellationTokenSource cts = new CancellationTokenSource();
+
+        private readonly TextFlowContainer text;
+
+        private long[] writes = new long[3];
+        private long[] reads = new long[3];
+        private Stopwatch stopwatch = Stopwatch.StartNew();
+
+        private int writeLag;
+        private int readLag;
+
+        public TestSceneTripleBufferOccupancy()
+        {
+            Add(text = new TextFlowContainer
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                AutoSizeAxes = Axes.Both
+            });
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            TripleBuffer<object> tripleBuffer = new TripleBuffer<object>();
+
+            new Thread(() =>
+            {
+                while (!cts.IsCancellationRequested)
+                {
+                    using (var write = tripleBuffer.GetForWrite())
+                        writes[write.Index]++;
+
+                    if (writeLag != 0)
+                        Thread.Sleep(writeLag);
+                }
+            }).Start();
+
+            new Thread(() =>
+            {
+                while (!cts.IsCancellationRequested)
+                {
+                    using (var read = tripleBuffer.GetForRead())
+                    {
+                        if (read != null)
+                            reads[read.Index]++;
+                    }
+
+                    if (readLag != 0)
+                        Thread.Sleep(readLag);
+                }
+            }).Start();
+
+            AddSliderStep("write lag", 0, 16, 0, v =>
+            {
+                writeLag = v;
+                reset();
+            });
+
+            AddSliderStep("read lag", 0, 16, 0, v =>
+            {
+                readLag = v;
+                reset();
+            });
+
+            reset();
+        }
+
+        private void reset()
+        {
+            writes = new long[3];
+            reads = new long[3];
+            stopwatch = Stopwatch.StartNew();
+        }
+
+        protected override void Update()
+        {
+            base.Update();
+
+            StringBuilder info = new StringBuilder();
+
+            double totalWrites = writes.Sum();
+            double totalReads = reads.Sum();
+
+            info.AppendLine("write occupancy:");
+            for (int i = 0; i < writes.Length; i++)
+                info.AppendLine($"{i}:   {writes[i] / totalWrites,-10:P}({writes[i]} / {totalWrites})");
+
+            info.AppendLine();
+
+            info.AppendLine("read occupancy:");
+            for (int i = 0; i < reads.Length; i++)
+                info.AppendLine($"{i}:   {reads[i] / totalReads,-10:P}({reads[i]} / {totalReads})");
+
+            info.AppendLine();
+
+            info.AppendLine($"Speed: {stopwatch.Elapsed.TotalMicroseconds / totalReads:0.00}us/read");
+
+            text.Text = info.ToString();
+        }
+
+        protected override void Dispose(bool isDisposing)
+        {
+            base.Dispose(isDisposing);
+            cts.Cancel();
+        }
+    }
+}