Prevent FIELD redraw flicker

engine/Age.Engine.Tests/ScriptPresentationBarrierTests.cs

@@ -0,0 +1,74 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Age.Engine.Hosting;
+using Xunit;
+
+public class ScriptPresentationBarrierTests
+{
+    [Fact]
+    public void ScriptBurstWithholdsPresentationUntilExit()
+    {
+        var barrier = new ScriptPresentationBarrier();
+
+        barrier.EnterScript();
+        Assert.False(barrier.TryEnterPresentation());
+
+        barrier.ExitScript();
+        Assert.True(barrier.TryEnterPresentation());
+        barrier.ExitPresentation();
+    }
+
+    [Fact]
+    public void NestedScriptsRemainOneAtomicBurst()
+    {
+        var barrier = new ScriptPresentationBarrier();
+
+        barrier.EnterScript();
+        barrier.EnterScript();
+        barrier.ExitScript();
+        Assert.False(barrier.TryEnterPresentation());
+
+        barrier.ExitScript();
+        Assert.True(barrier.TryEnterPresentation());
+        barrier.ExitPresentation();
+    }
+
+    [Fact]
+    public void ServiceBoundaryTemporarilyAllowsPresentation()
+    {
+        var barrier = new ScriptPresentationBarrier();
+
+        barrier.EnterScript();
+        bool suspended = barrier.SuspendScript();
+        Assert.True(suspended);
+        Assert.True(barrier.TryEnterPresentation());
+        barrier.ExitPresentation();
+
+        barrier.ResumeScript(suspended);
+        Assert.False(barrier.TryEnterPresentation());
+        barrier.ExitScript();
+    }
+
+    [Fact]
+    public async Task RenderThreadCannotEnterWhileVmThreadIsRebuilding()
+    {
+        var barrier = new ScriptPresentationBarrier();
+        using var entered = new ManualResetEventSlim();
+        using var release = new ManualResetEventSlim();
+        Task vmBurst = Task.Run(() =>
+        {
+            barrier.EnterScript();
+            entered.Set();
+            release.Wait();
+            barrier.ExitScript();
+        });
+
+        await Task.Run(entered.Wait);
+        Assert.False(barrier.TryEnterPresentation());
+
+        release.Set();
+        await vmBurst;
+        Assert.True(barrier.TryEnterPresentation());
+        barrier.ExitPresentation();
+    }
+}