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[Perf] Reduce allocations in inherited BindingContext propagation #34135

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[Perf] Reduce allocations in inherited BindingContext propagation #34135

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9d09d7c
Reduce allocations in inherited BindingContext propagation
simonrozsival Feb 19, 2026
dcd3a94
Simplify ApplyBindings to iterate _properties.Values directly
simonrozsival Feb 19, 2026
d65b88e
Restore ToArray snapshot in ApplyBindings for re-entrancy safety
simonrozsival Mar 11, 2026
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12 changes: 8 additions & 4 deletions src/Controls/src/Core/BindableObject.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -363,7 +363,10 @@ public static void SetInheritedBindingContext(BindableObject bindable, object va
}
else
{
bindable._inheritedContext = new WeakReference(value);
if (bindable._inheritedContext is not null)
bindable._inheritedContext.Target = value;
else
bindable._inheritedContext = new WeakReference(value);
bindable.ApplyBindings(fromBindingContextChanged: true);
bindable.OnBindingContextChanged();
}
Expand Down Expand Up @@ -692,11 +695,12 @@ private protected virtual void OnBindablePropertySet(BindableProperty property,

void ApplyBindings(bool fromBindingContextChanged)
{
var prop = _properties.Values.ToArray();
// Snapshot the property contexts — ApplyBinding can trigger re-entrant
// property changes (via callbacks) that modify _properties mid-iteration.
var contexts = _properties.Values.ToArray();

for (int i = 0, propLength = prop.Length; i < propLength; i++)
foreach (var context in contexts)
{
BindablePropertyContext context = prop[i];
if (ReferenceEquals(context.Property, BindingContextProperty))
{
// BindingContextProperty Binding is handled separately within SetInheritedBindingContext
Expand Down
194 changes: 39 additions & 155 deletions src/Core/tests/Benchmarks/Benchmarks/BindableObjectAllocBenchmarker.cs
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Expand Up @@ -6,52 +6,21 @@ namespace Microsoft.Maui.Handlers.Benchmarks
[MemoryDiagnoser]
public class BindableObjectAllocBenchmarker
{
// --- #34092: Cached PropertyChangedEventArgs / PropertyChangingEventArgs ---

/// <summary>
/// Sets the same property repeatedly to measure PropertyChanged/Changing EventArgs allocations.
/// Before: new PropertyChangedEventArgs + new PropertyChangingEventArgs per call.
/// After: cached per BindableProperty.
/// </summary>
[Benchmark]
public void SetProperty_EventArgsAlloc()
Label _label;
Label _child;
VerticalStackLayout _deepTreeLeaf;
VerticalStackLayout _flatLayout;
object _contextA, _contextB;
bool _toggle;

[GlobalSetup]
public void Setup()
{
var label = new Label();
for (int i = 0; i < 1_000; i++)
{
label.Text = "a";
label.Text = "b";
}
}
_label = new Label();
_contextA = new object();
_contextB = new object();

/// <summary>
/// Sets multiple different properties to show caching benefit across properties.
/// </summary>
[Benchmark]
public void SetMultipleProperties_EventArgsAlloc()
{
var entry = new Entry();
for (int i = 0; i < 500; i++)
{
entry.Text = "a";
entry.Placeholder = "p";
entry.FontSize = 14 + (i % 3);
entry.Text = "b";
entry.Placeholder = "q";
}
}

// --- #34093: Reuse ElementEventArgs in tree propagation ---

/// <summary>
/// Adds children to a deep hierarchy, triggering DescendantAdded propagation.
/// Before: new ElementEventArgs at every tree level.
/// After: single ElementEventArgs reused through recursion.
/// </summary>
[Benchmark]
public void AddChildren_DeepTree_ElementEventArgs()
{
// Build a 10-level deep tree
// 10-level deep tree for DescendantAdded/Removed propagation
var root = new VerticalStackLayout();
var current = root;
for (int depth = 0; depth < 10; depth++)
Expand All @@ -60,133 +29,48 @@ public void AddChildren_DeepTree_ElementEventArgs()
current.Add(child);
current = child;
}
_child = new Label();
_deepTreeLeaf = current;

// Add 100 leaves at the bottom — each fires DescendantAdded 10 levels up
for (int i = 0; i < 100; i++)
{
current.Add(new Label());
}
// Flat layout with 200 children for BindingContext propagation
_flatLayout = new VerticalStackLayout();
for (int i = 0; i < 200; i++)
_flatLayout.Add(new Label());
}

/// <summary>
/// Removes children from a deep hierarchy, triggering DescendantRemoved propagation.
/// </summary>
[Benchmark]
public void RemoveChildren_DeepTree_ElementEventArgs()
{
var root = new VerticalStackLayout();
var current = root;
for (int depth = 0; depth < 10; depth++)
{
var child = new VerticalStackLayout();
current.Add(child);
current = child;
}

var labels = new Label[100];
for (int i = 0; i < 100; i++)
{
labels[i] = new Label();
current.Add(labels[i]);
}
// --- #34092: Cached PropertyChangedEventArgs / PropertyChangingEventArgs ---

for (int i = 0; i < 100; i++)
{
current.Remove(labels[i]);
}
[Benchmark(Description = "SetValue (EventArgs)")]
public void SetProperty_EventArgs()
{
_toggle = !_toggle;
_label.Text = _toggle ? "a" : "b";
}

// --- #34129: BindingContext propagation (WeakReference reuse + .ToArray() elimination) ---
// --- #34093: Reuse ElementEventArgs in tree propagation ---

class SimpleViewModel
[Benchmark(Description = "Add+Remove child (10-deep tree)")]
public void AddRemoveChild_DeepTree()
{
public string Name { get; set; } = "Test";
_deepTreeLeaf.Add(_child);
_deepTreeLeaf.Remove(_child);
}

/// <summary>
/// Sets BindingContext on a flat layout with many children.
/// Before: new WeakReference per child + .ToArray() on each child's _properties.
/// After: reuse WeakReference.Target + foreach on dictionary directly.
/// </summary>
[Benchmark]
// --- #34129: BindingContext propagation (WeakReference reuse + .ToArray() elimination) ---

[Benchmark(Description = "Set BindingContext (200 children)")]
public void SetBindingContext_FlatTree()
{
var layout = new VerticalStackLayout();
for (int i = 0; i < 200; i++)
{
layout.Add(new Label());
}

var vm = new SimpleViewModel();
for (int i = 0; i < 10; i++)
{
layout.BindingContext = vm;
layout.BindingContext = null;
}
}

/// <summary>
/// Sets BindingContext on a deep tree where children have bindings.
/// This is the worst-case hot path: ApplyBindings + WeakReference for every descendant.
/// </summary>
[Benchmark]
public void SetBindingContext_DeepTreeWithBindings()
{
var root = new VerticalStackLayout();
var current = root;

for (int depth = 0; depth < 5; depth++)
{
var child = new VerticalStackLayout();
current.Add(child);
current = child;
}

for (int i = 0; i < 50; i++)
{
var label = new Label();
label.SetBinding(Label.TextProperty, new Binding("Name"));
current.Add(label);
}

var vm = new SimpleViewModel();
for (int i = 0; i < 20; i++)
{
root.BindingContext = vm;
root.BindingContext = null;
}
_toggle = !_toggle;
_flatLayout.BindingContext = _toggle ? _contextA : _contextB;
}

// --- #34131: Lazy _triggerSpecificity dictionary ---

/// <summary>
/// Creates many BindableObjects (Labels) that never use triggers.
/// Before: each allocates Dictionary&lt;TriggerBase, SetterSpecificity&gt;.
/// After: dictionary is null until first trigger attachment.
/// </summary>
[Benchmark]
public Label[] CreateManyLabels_NoTriggers()
{
var labels = new Label[1_000];
for (int i = 0; i < 1_000; i++)
{
labels[i] = new Label();
}
return labels;
}
[Benchmark(Description = "new Label()")]
public Label CreateLabel() => new Label();

/// <summary>
/// Creates many Entries (more complex BindableObject) without triggers.
/// </summary>
[Benchmark]
public Entry[] CreateManyEntries_NoTriggers()
{
var entries = new Entry[500];
for (int i = 0; i < 500; i++)
{
entries[i] = new Entry();
}
return entries;
}
[Benchmark(Description = "new Entry()")]
public Entry CreateEntry() => new Entry();
}
}
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