delete target object from event handler collections when it has no more event handlers

lostmsu · lostmsu · commit 9ace8dcc35c7 · 2022-10-13T12:12:06.000-07:00
fixes #1972
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -13,6 +13,8 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 
 ### Fixed
 
+-   Fixed objects leaking when Python attached event handlers to them even if they were later removed
+
 
 ## [3.0.0](https://github.com/pythonnet/pythonnet/releases/tag/v3.0.0) - 2022-09-29
 
diff --git a/src/embed_tests/Events.cs b/src/embed_tests/Events.cs
@@ -0,0 +1,74 @@
+using System;
+using System.Diagnostics;
+using System.Threading;
+
+using NUnit.Framework;
+
+using Python.Runtime;
+
+namespace Python.EmbeddingTest;
+
+public class Events
+{
+    [OneTimeSetUp]
+    public void SetUp()
+    {
+        PythonEngine.Initialize();
+    }
+
+    [OneTimeTearDown]
+    public void Dispose()
+    {
+        PythonEngine.Shutdown();
+    }
+
+    [Test]
+    public void UsingDoesNotLeak()
+    {
+        using var scope = Py.CreateScope();
+        scope.Exec(@"
+import gc
+
+from Python.EmbeddingTest import ClassWithEventHandler
+
+def event_handler():
+    pass
+
+for _ in range(2000):
+    example = ClassWithEventHandler()
+    example.LeakEvent += event_handler
+    example.LeakEvent -= event_handler
+    example.Dispose()
+    del example
+
+gc.collect()
+");
+        Runtime.Runtime.TryCollectingGarbage(10);
+        Assert.AreEqual(0, ClassWithEventHandler.alive);
+    }
+}
+
+public class ClassWithEventHandler : IDisposable
+{
+    internal static int alive;
+
+    public event EventHandler LeakEvent;
+    private Array arr;  // dummy array to exacerbate memory leak
+
+    public ClassWithEventHandler()
+    {
+        Interlocked.Increment(ref alive);
+        this.arr = new int[800];
+    }
+
+    public void Dispose()
+    {
+        this.LeakEvent = null;
+        Debug.WriteLine(GC.GetTotalMemory(true));
+    }
+
+    ~ClassWithEventHandler()
+    {
+        Interlocked.Decrement(ref alive);
+    }
+}
diff --git a/src/runtime/Util/EventHandlerCollection.cs b/src/runtime/Util/EventHandlerCollection.cs
@@ -99,6 +99,10 @@ internal bool RemoveEventHandler(BorrowedReference target, BorrowedReference han
                 continue;
             }
             list.RemoveAt(i);
+            if (list.Count == 0)
+            {
+                Remove(key);
+            }
             return true;
         }
 
