Clean up object pools and improve PooledHashSet<T> by DustinCampbell · Pull Request #12406 · dotnet/razor

DustinCampbell · 2025-10-28T21:21:06Z

This represents some clean-up and a small performance improvement that I've intended to do for a long while. In fact, it's been sitting on my machine across a handful of branches for months. So, I decided to bring it together and submit a PR.

Key Changes:

The custom pool classes are now instance classes rather than static classes. So, it's not possible to create an instance of an ArrayBuilderPool<T> rather than an ObjectPool<ImmutableArray<T>.Builder>.
Introduce a SpecializedPools static class that pulls together StringHashSetPool, StringDictionaryPool<TValue>, and ReferenceEqualityHashSetPool<T>.
Add MaximumObjectSize as a knob when creating new custom pools to avoid always having to create a new IPooledObjectPolicy<T> implementation.
Introduce an IPoolableObject interface and way to create pools of IPoolableObjects.
Improve PooledHashSet<T> to avoid acquiring a HashSet<T> from a pool until there are at least two items.

CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2826683&view=results
Test Insertion: https://dev.azure.com/devdiv/DevDiv/_git/VS/pullrequest/684259
Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2826684&view=results

Convert the various pool classes, such as ListPool<T>, from static to instance classes.

Introduce a SpecializedPools static class that contains the special pools for ReferenceEqualityComparer<T> and string hash sets, and string dictionaries.

Introduce CustomObjectPool<T> base type for custom pools, such as ListPool<T>. Provides a PooledObjectPolicy abstract class that implements IPooledObjectPolicy<T>.

This is based on Roslyn's Optional<T>, which is similar to Nullable<T> except that it can hold reference types and does not throw when `Value` is accessed and `HasValue` is false. It is particular useful for long lists of optional parameters. Note: This type is public because Razor was currently using Roslyn's Optional<T> in a couple of public places, and those are now using Razor's Optional<T>.

Now that there's a parameter for setting the maximum object size of a ListPool<T>, AbstractRazorSemanticTokensInfoService no longer needs a custom Policy object.

Introduce an IPoolableObject interface that allows a pooled object to be reset before being returned to a pool. Also, add DefaultPool.Create(...) overloads for constructing pools for IPooledObjects.

By making each of the ClassifiedSpanVisitor types implement IPoolableObject their custom Policy objects can be removed.

By making JsonDataReader and JsonDataWriter implement IPoolableObject their custom Policy objects can be removed.

Allow all TagHelperObjectBuilder<T> subtypes to remove their custom policy objects.

Allows the custom Policy type to be removed from DefaultRazorTagHelperContextDiscoveryPhase.

This change reworks PooledHashSet<T> and adds two features: 1. It is now possible to pass an IEqualityComparer<T> or a HashSetPool<T> when constructing a PooledHashSet<T>. A HashSetPool<T> will be chosen based on the IEqualityComparer<T>, or a new HashSet<T> will be created if a default pool doesn't exist. 2. A HashSet<T> won't be acquired from the pool (or created) until the set would contain at least two items.

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src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Legacy/ParserContext.cs

...mpiler/Microsoft.CodeAnalysis.Razor.Compiler/src/CSharp/DefaultTagHelperDescriptorFactory.cs

...deAnalysis.Razor.Workspaces/Serialization/MessagePack/Formatters/SerializerCachingOptions.cs

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/PooledObjects/PooledHashSet`1.cs

ToddGrun

DustinCampbell added 15 commits October 28, 2025 09:18

Convert pools to instance classes

78c00bc

Convert the various pool classes, such as ListPool<T>, from static to instance classes.

Introduce SpecializedPools static class

a045725

Introduce a SpecializedPools static class that contains the special pools for ReferenceEqualityComparer<T> and string hash sets, and string dictionaries.

Introduce CustomObjectPool<T> base type

3f4de6c

Introduce CustomObjectPool<T> base type for custom pools, such as ListPool<T>. Provides a PooledObjectPolicy abstract class that implements IPooledObjectPolicy<T>.

Update custom pools to provide more knobs for controlling policy

eb4da6b

Add helper consts to CustomObjectPool<T>

2a9a770

Replace ObjectPool<List<SemanticRange>> with ListPool<SemanticRange>

4bb64ab

Now that there's a parameter for setting the maximum object size of a ListPool<T>, AbstractRazorSemanticTokensInfoService no longer needs a custom Policy object.

Introduce IPoolableObject and DefaultPool.Create overloads

0bb3a87

Introduce an IPoolableObject interface that allows a pooled object to be reset before being returned to a pool. Also, add DefaultPool.Create(...) overloads for constructing pools for IPooledObjects.

Make ClassifiedSpanVisitors implement IPoolableObject

7df7ba7

By making each of the ClassifiedSpanVisitor types implement IPoolableObject their custom Policy objects can be removed.

Make JsonDataReader and JsonDataWriter implement IPoolableObject

9e1da0a

By making JsonDataReader and JsonDataWriter implement IPoolableObject their custom Policy objects can be removed.

Make TagHelperObjectBuilder<T> implement IPoolable

4a100b4

Allow all TagHelperObjectBuilder<T> subtypes to remove their custom policy objects.

Make DirectiveVisitor implement IPoolableObject

8954678

Allows the custom Policy type to be removed from DefaultRazorTagHelperContextDiscoveryPhase.

Add custom HashingTypePool for Checksum.Builder

525d170

When appropriate, use custom pool types rather than ObjectPool<T>

dd3344f

DustinCampbell requested a review from a team as a code owner October 28, 2025 21:21

Ensure custom pool policies corrently use default values when unspeci…

1c5553e

…fied

davidwengier approved these changes Oct 28, 2025

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