Backport #4227 to 4.x: Let a reused engine discard the host objects its warmed caches hold

Jint.Tests.PublicInterface/HostInterpreterCacheDiscardTests.cs

@@ -0,0 +1,63 @@
+#nullable enable
+
+using System;
+using System.Runtime.CompilerServices;
+
+namespace Jint.Tests.PublicInterface;
+
+/// <summary>
+/// <c>engine.Advanced.DiscardInterpreterCaches()</c> from the embedder's side: the engine-pool shape — capture
+/// once, evaluate a cached prepared script with per-request host globals, restore — with the discard added on
+/// return, which is the only way a pooled engine stops keeping the last request's services alive through a
+/// warmed call site.
+/// </summary>
+[CollectionDefinition(nameof(HostInterpreterCacheDiscardTests), DisableParallelization = true)]
+[Collection(nameof(HostInterpreterCacheDiscardTests))]
+public class HostInterpreterCacheDiscardTests
+{
+    private sealed class RequestServices
+    {
+        public string Name => "services";
+    }
+
+    [Fact]
+    public void APooledEngineReleasesTheLastRequestsServicesAfterADiscard()
+    {
+        var engine = new Engine();
+        var snapshot = engine.Advanced.CaptureGlobalSnapshot();
+        var script = Engine.PrepareScript("describe(ctx.Name)");
+
+        RunRequest(engine, snapshot, script);
+        var services = RunRequest(engine, snapshot, script);
+
+        engine.Advanced.DiscardInterpreterCaches();
+        GC.Collect(2, GCCollectionMode.Forced, blocking: true);
+        GC.WaitForPendingFinalizers();
+        GC.Collect(2, GCCollectionMode.Forced, blocking: true);
+
+        services.IsAlive.Should().BeFalse("nothing in a restored, discarded engine may reach a finished request's services");
+
+        // the engine stays fully usable and computes the same thing
+        RunRequest(engine, snapshot, script);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static WeakReference RunRequest(Engine engine, GlobalSnapshot snapshot, Prepared<Script> script)
+    {
+        var services = new RequestServices();
+        engine.SetValue("ctx", services);
+        engine.SetValue("describe", new Func<string, string>(value => value + ":" + services.Name));
+        engine.Evaluate(script).AsString().Should().Be("services:services");
+        engine.Advanced.RestoreGlobalSnapshot(snapshot);
+        return new WeakReference(services);
+    }
+
+    [Fact]
+    public void DiscardingWhileAnEvaluationIsInProgressIsRefused()
+    {
+        var engine = new Engine();
+        engine.SetValue("discard", new Action(() => engine.Advanced.DiscardInterpreterCaches()));
+
+        Assert.Throws<InvalidOperationException>(() => engine.Execute("discard()"));
+    }
+}

Jint.Tests.PublicInterface/Verify/PublicApiTest_net10.0.verified.txt

@@ -92,6 +92,7 @@ namespace Jint
             public Jint.GlobalSnapshot CaptureGlobalSnapshot() { }
             public Jint.Native.Object.ObjectInstance CreateProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
             public Jint.Runtime.Interop.RevocableProxy CreateRevocableProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
+            public void DiscardInterpreterCaches() { }
             public Jint.InteropConversionDiagnostics GetInteropConversionDiagnostics() { }
             public Jint.ObjectRepresentation GetObjectRepresentation(Jint.Native.Object.ObjectInstance value) { }
             public Jint.Native.Object.PropertyAccessSemantics GetPropertyAccessSemantics(Jint.Native.Object.ObjectInstance value) { }

Jint.Tests.PublicInterface/Verify/PublicApiTest_net462.verified.txt

@@ -92,6 +92,7 @@ namespace Jint
             public Jint.GlobalSnapshot CaptureGlobalSnapshot() { }
             public Jint.Native.Object.ObjectInstance CreateProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
             public Jint.Runtime.Interop.RevocableProxy CreateRevocableProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
+            public void DiscardInterpreterCaches() { }
             public Jint.InteropConversionDiagnostics GetInteropConversionDiagnostics() { }
             public Jint.ObjectRepresentation GetObjectRepresentation(Jint.Native.Object.ObjectInstance value) { }
             public Jint.Native.Object.PropertyAccessSemantics GetPropertyAccessSemantics(Jint.Native.Object.ObjectInstance value) { }

Jint.Tests.PublicInterface/Verify/PublicApiTest_net8.0.verified.txt

@@ -92,6 +92,7 @@ namespace Jint
             public Jint.GlobalSnapshot CaptureGlobalSnapshot() { }
             public Jint.Native.Object.ObjectInstance CreateProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
             public Jint.Runtime.Interop.RevocableProxy CreateRevocableProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
+            public void DiscardInterpreterCaches() { }
             public Jint.InteropConversionDiagnostics GetInteropConversionDiagnostics() { }
             public Jint.ObjectRepresentation GetObjectRepresentation(Jint.Native.Object.ObjectInstance value) { }
             public Jint.Native.Object.PropertyAccessSemantics GetPropertyAccessSemantics(Jint.Native.Object.ObjectInstance value) { }

Jint.Tests.PublicInterface/Verify/PublicApiTest_netstandard2.0.verified.txt

@@ -92,6 +92,7 @@ namespace Jint
             public Jint.GlobalSnapshot CaptureGlobalSnapshot() { }
             public Jint.Native.Object.ObjectInstance CreateProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
             public Jint.Runtime.Interop.RevocableProxy CreateRevocableProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
+            public void DiscardInterpreterCaches() { }
             public Jint.InteropConversionDiagnostics GetInteropConversionDiagnostics() { }
             public Jint.ObjectRepresentation GetObjectRepresentation(Jint.Native.Object.ObjectInstance value) { }
             public Jint.Native.Object.PropertyAccessSemantics GetPropertyAccessSemantics(Jint.Native.Object.ObjectInstance value) { }

Jint.Tests.PublicInterface/Verify/PublicApiTest_netstandard2.1.verified.txt

@@ -92,6 +92,7 @@ namespace Jint
             public Jint.GlobalSnapshot CaptureGlobalSnapshot() { }
             public Jint.Native.Object.ObjectInstance CreateProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
             public Jint.Runtime.Interop.RevocableProxy CreateRevocableProxy(Jint.Native.Object.ObjectInstance target, Jint.Runtime.Interop.ProxyHandler handler) { }
+            public void DiscardInterpreterCaches() { }
             public Jint.InteropConversionDiagnostics GetInteropConversionDiagnostics() { }
             public Jint.ObjectRepresentation GetObjectRepresentation(Jint.Native.Object.ObjectInstance value) { }
             public Jint.Native.Object.PropertyAccessSemantics GetPropertyAccessSemantics(Jint.Native.Object.ObjectInstance value) { }