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Fix Repeater memoization memory leak
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If the ConditionalWeakTable references itself, it will get leaked by
.NET Core GC: dotnet/runtime#12255

Fortunately, we don't really need the ConditinalWeakTable here:
* Repeater should generally be a short-lived object, so
   strong references will also be collected reasonably soon
* Between Load and PreRender, the viewmodels were pinned
   in the DataContext of all children and the children are in Children
   collection. Only after PreRender could those references be useful,
   but we can as well Clear the dictionary at that point.

Co-authored-by: Adam Štěpánek <[email protected]>
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exyi and cafour committed Dec 1, 2024
1 parent f74c4ea commit d3b55c7
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Showing 4 changed files with 175 additions and 7 deletions.
Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,7 @@ private void AddNodeErrors(DothtmlNode node, int priority)
/// * the locations are processed using MapBindingLocation to make them useful in the context of a dothtml file </summary>
Dictionary<Exception, DotvvmCompilationSourceLocation?> AnnotateBindingExceptionWithLocation(ResolvedBinding binding, DotvvmProperty? relatedProperty, IEnumerable<Exception> errors)
{
var result = new Dictionary<Exception, DotvvmCompilationSourceLocation?>(new ReferenceEqualityComparer<Exception>());
var result = new Dictionary<Exception, DotvvmCompilationSourceLocation?>(ReferenceEqualityComparer<Exception>.Instance);
void recurse(Exception exception, DotvvmCompilationSourceLocation? location)
{
if (result.ContainsKey(exception))
Expand Down
15 changes: 11 additions & 4 deletions src/Framework/Framework/Controls/Repeater.cs
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
using System.Linq;
using System.Runtime.CompilerServices;
using System.Collections.Generic;
using DotVVM.Framework.Utils;

namespace DotVVM.Framework.Controls
{
Expand Down Expand Up @@ -139,6 +140,7 @@ protected internal override void OnLoad(IDotvvmRequestContext context)
protected internal override void OnPreRender(IDotvvmRequestContext context)
{
SetChildren(context, renderClientTemplate: !RenderOnServer, memoizeReferences: false);
childrenCache.Clear(); // not going to need the unreferenced children anymore
base.OnPreRender(context);
}

Expand Down Expand Up @@ -248,7 +250,7 @@ private DotvvmControl CreateEmptyItem(IDotvvmRequestContext context)
return emptyDataContainer;
}

private ConditionalWeakTable<object, DataItemContainer> childrenCache = new ConditionalWeakTable<object, DataItemContainer>();
private readonly Dictionary<object, DataItemContainer> childrenCache = new(ReferenceEqualityComparer<object>.Instance);
private DotvvmControl AddItem(IList<DotvvmControl> c, IDotvvmRequestContext context, object? item = null, int? index = null, bool allowMemoizationRetrieve = false, bool allowMemoizationStore = false)
{
if (allowMemoizationRetrieve && item != null && childrenCache.TryGetValue(item, out var container2) && container2.Parent == null)
Expand Down Expand Up @@ -276,8 +278,12 @@ private DotvvmControl AddItem(IList<DotvvmControl> c, IDotvvmRequestContext cont
// write it to the cache after the content is build. If it would be before that, exception could be suppressed
if (allowMemoizationStore && item != null)
{
// this GetValue call adds the value without raising exception when the value is already added...
childrenCache.GetValue(item, _ => container);
#if DotNetCore
childrenCache.TryAdd(item, container);
#else
if (!childrenCache.ContainsKey(item))
childrenCache.Add(item, container);
#endif
}

return container;
Expand Down Expand Up @@ -306,14 +312,15 @@ private void SetChildren(IDotvvmRequestContext context, bool renderClientTemplat
if (DataSource != null)
{
var index = 0;
var isCommand = context.RequestType == DotvvmRequestType.Command; // on GET request we are not initializing the Repeater twice
foreach (var item in GetIEnumerableFromDataSource()!)
{
if (SeparatorTemplate != null && index > 0)
{
AddSeparator(Children, context);
}
AddItem(Children, context, item, index,
allowMemoizationRetrieve: context.RequestType == DotvvmRequestType.Command && !memoizeReferences, // on GET request we are not initializing the Repeater twice
allowMemoizationRetrieve: isCommand && !memoizeReferences,
allowMemoizationStore: memoizeReferences
);
index++;
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8 changes: 6 additions & 2 deletions src/Framework/Framework/Utils/ReferenceEqualityComparer.cs
Original file line number Diff line number Diff line change
@@ -1,12 +1,16 @@
using System.Collections.Generic;
using System.Runtime.CompilerServices;

namespace DotVVM.Framework.Utils
{
// TODO next version: Replace with System.Collections.Generic.ReferenceEqualityComparer
internal class ReferenceEqualityComparer<T> : IEqualityComparer<T>
where T : class
{
public bool Equals(T? x, T? y) => ReferenceEquals(x, y);
public static ReferenceEqualityComparer<T> Instance { get; } = new ReferenceEqualityComparer<T>();


public int GetHashCode(T obj) => obj?.GetHashCode() ?? 0;
public bool Equals(T? x, T? y) => ReferenceEquals(x, y);
public int GetHashCode(T obj) => obj == null ? 0 : RuntimeHelpers.GetHashCode(obj);
}
}
157 changes: 157 additions & 0 deletions src/Tests/Runtime/RepeaterMemoizationTest.cs
Original file line number Diff line number Diff line change
@@ -0,0 +1,157 @@
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using AngleSharp.Io;
using DotVVM.Framework.Binding.Expressions;
using DotVVM.Framework.Compilation.ControlTree;
using DotVVM.Framework.Controls;
using DotVVM.Framework.Controls.Infrastructure;
using DotVVM.Framework.Hosting;
using DotVVM.Framework.Testing;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace DotVVM.Framework.Tests.Runtime
{
[TestClass]
public class RepeaterMemoizationTest: DotvvmControlTestBase
{
(Repeater, TestDotvvmRequestContext) Init<T>(T viewModel, ITemplate template)
where T: IEnumerable
{
var dataContextStack = DataContextStack.Create(viewModel.GetType());
var repeater = new Repeater() {
DataSource = ValueBindingExpression.CreateBinding(BindingService, h => (T)h[0], dataContextStack),
ItemTemplate = template
};
repeater.SetValue(RenderSettings.ModeProperty, RenderMode.Client);

var context = CreateContext(viewModel);

return (repeater, context);
}

[DataTestMethod]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.Command, RenderMode.Client)]
[DataRow(DotvvmRequestType.Command, RenderMode.Server)]
public void Repeater_TemplateInitializedOnce(DotvvmRequestType requestType, RenderMode renderMode)
{
var templateInits = new List<string>();
var (repeater, context) = Init(new[] { "ROW 1", "ROW 2", "ROW 3" }, new DelegateTemplate((sp, body) => {

body.AppendChildren(new Literal("test"));
templateInits.Add((string)body.DataContext);
}));
repeater.SetValue(RenderSettings.ModeProperty, renderMode);
context.RequestType = requestType;
var html = InvokeLifecycleAndRender(repeater, context);

Console.WriteLine("Template inits: " + string.Join(", ", templateInits.Select(i => i ?? "<null>")));

if (renderMode == RenderMode.Client)
{
XAssert.Equal(["ROW 1", "ROW 2", "ROW 3", null], templateInits);
}
else
{
XAssert.Equal(["ROW 1", "ROW 2", "ROW 3"], templateInits);
}
}

[DataTestMethod]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.Command, RenderMode.Client)]
[DataRow(DotvvmRequestType.Command, RenderMode.Server)]
public void Repeater_ViewModelChange(DotvvmRequestType requestType, RenderMode renderMode)
{
var templateInits = new List<string>();
var viewModel = new[] { "ROW 1", "ROW 2", "ROW 3" };
var (repeater, context) = Init(viewModel, new DelegateTemplate((sp, body) => {

body.AppendChildren(new Literal("test"));
templateInits.Add((string)body.DataContext);
}));
context.RequestType = requestType;
repeater.SetValue(RenderSettings.ModeProperty, renderMode);

var view = new DotvvmView();
view.Children.Add(repeater);
view.SetValue(Internal.RequestContextProperty, context);
view.DataContext = context.ViewModel;

// Run Load event

DotvvmControlCollection.InvokePageLifeCycleEventRecursive(view, LifeCycleEventType.Load, context);
Console.WriteLine("Template inits (Load): " + string.Join(", ", templateInits.Select(i => i ?? "<null>")));

if (requestType == DotvvmRequestType.Command)
XAssert.Equal(["ROW 1", "ROW 2", "ROW 3"], templateInits);
else
XAssert.Equal([], templateInits);

// Continue with PreRender and Render after shuffling the view model

view.DataContext = context.ViewModel = viewModel = [ viewModel[1], viewModel[2], "ROW 4", viewModel[1] ];

var html = InvokeLifecycleAndRender(view, context);

Console.WriteLine("Template inits (Render): " + string.Join(", ", templateInits.Select(i => i ?? "<null>")));

string[] nullIfClient = renderMode == RenderMode.Client ? [ null ] : [];

if (requestType == DotvvmRequestType.Command)
{
XAssert.Equal(["ROW 1", "ROW 2", "ROW 3", /* Load end */ "ROW 4", "ROW 2", ..nullIfClient], templateInits);
}
else
{
XAssert.Equal(["ROW 2", "ROW 3", "ROW 4", "ROW 2", ..nullIfClient], templateInits);
}
}

[DataTestMethod]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.Navigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Client)]
[DataRow(DotvvmRequestType.SpaNavigate, RenderMode.Server)]
[DataRow(DotvvmRequestType.Command, RenderMode.Client)]
[DataRow(DotvvmRequestType.Command, RenderMode.Server)]
public void Repeater_IsCollectible(DotvvmRequestType requestType, RenderMode renderMode)
{
var (repeaterRef, contextRef, viewModelRef) = RunLifecycle(requestType, renderMode);

for (int i = 0; i < 100; i++) // single collection is enough normally, but just to be sure it's not flaky on CI...
{
GC.Collect(2, GCCollectionMode.Forced, blocking: true);

Console.WriteLine($"GC Collect #{i} ({repeaterRef.IsAlive}, {contextRef.IsAlive}, {viewModelRef.IsAlive})");

if (!repeaterRef.IsAlive || !contextRef.IsAlive || !viewModelRef.IsAlive)
{
break;
}
}

XAssert.Equal((false, false, false), (repeaterRef.IsAlive, contextRef.IsAlive, viewModelRef.IsAlive));

(WeakReference, WeakReference, WeakReference) RunLifecycle(DotvvmRequestType requestType, RenderMode renderMode)
{
var (repeater, context) = Init(new[] { "ROW 1", "ROW 2", "ROW 3" }, new DelegateTemplate((sp, body) => {
body.AppendChildren(new Literal("test"));
}));
repeater.SetValue(RenderSettings.ModeProperty, renderMode);
context.RequestType = requestType;
var html = InvokeLifecycleAndRender(repeater, context);

return (new WeakReference(repeater), new WeakReference(context), new WeakReference(context.ViewModel));
}
}
}
}

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