[StaticWebAssets] Process collection properties with amortized allocation #49682

javiercn · 2025-07-08T09:30:16Z

Introduces methods for populating existing collections of values.
Reuses well-known values during serialization and deserialization.

Performance Results by Component

1. StaticWebAssetEndpointProperty Benchmarks

.NET 10.0 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	651.8 ns	4.64 ns	4.12 ns	0.0372	952 B	Baseline
PopulateFromMetadataValue_New	285.2 ns	1.48 ns	1.31 ns	0.0067	168 B	56% Faster ✅
ToMetadataValue_Current	254.6 ns	1.07 ns	0.95 ns	0.0105	264 B	Baseline
ToMetadataValue_New	211.9 ns	2.78 ns	2.60 ns	0.0105	264 B	17% Faster ✅

.NET Framework 4.8.1 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	2,493.7 ns	25.82 ns	22.89 ns	0.1564	987 B	Baseline
PopulateFromMetadataValue_New	1,486.6 ns	8.64 ns	7.66 ns	0.0267	177 B	40% Faster ✅
ToMetadataValue_Current	1,014.8 ns	5.54 ns	4.91 ns	0.0420	273 B	Baseline
ToMetadataValue_New	947.4 ns	18.20 ns	15.19 ns	0.0429	273 B	7% Faster ✅

2. StaticWebAssetEndpointResponseHeader Benchmarks

.NET 10.0 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	1,929.1 ns	33.32 ns	29.54 ns	0.0725	1896 B	Baseline
PopulateFromMetadataValue_New	851.0 ns	10.57 ns	8.82 ns	0.0057	160 B	56% Faster ✅
ToMetadataValue_Current	745.6 ns	2.71 ns	2.53 ns	0.0296	752 B	Baseline
ToMetadataValue_New	637.3 ns	2.51 ns	2.35 ns	0.0296	752 B	15% Faster ✅

.NET Framework 4.8.1 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	8.204 us	0.0517 us	0.0458 us	0.3052	2014 B	Baseline
PopulateFromMetadataValue_New	4.922 us	0.0817 us	0.0973 us	0.0229	177 B	40% Faster ✅
ToMetadataValue_Current	2.946 us	0.0271 us	0.0253 us	0.1183	762 B	Baseline
ToMetadataValue_New	2.838 us	0.0247 us	0.0231 us	0.1183	762 B	4% Faster ✅

3. StaticWebAssetEndpointSelector Benchmarks

.NET 10.0 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	845.8 ns	11.52 ns	10.22 ns	0.0410	1040 B	Baseline
PopulateFromMetadataValue_New	339.2 ns	1.86 ns	1.65 ns	0.0033	88 B	60% Faster ✅
ToMetadataValue_Current	316.0 ns	2.26 ns	2.00 ns	0.0110	280 B	Baseline
ToMetadataValue_New	283.0 ns	2.45 ns	2.29 ns	0.0110	280 B	10% Faster ✅

.NET Framework 4.8.1 Results

Method	Mean	Error	StdDev	Gen0	Allocated	Performance
FromMetadataValue_Current	3.131 us	0.0616 us	0.0633 us	0.1678	1075 B	Baseline
PopulateFromMetadataValue_New	1.838 us	0.0136 us	0.0114 us	0.0134	88 B	41% Faster ✅
ToMetadataValue_Current	1.192 us	0.0048 us	0.0040 us	0.0458	289 B	Baseline
ToMetadataValue_New	1.131 us	0.0127 us	0.0112 us	0.0458	289 B	5% Faster ✅

dotnet-policy-service · 2025-07-08T09:30:54Z

Thanks for your PR, @@javiercn.
To learn about the PR process and branching schedule of this repo, please take a look at the SDK PR Guide.

src/StaticWebAssetsSdk/Tasks/Utils/PooledArrayBufferWriter.cs

…tions This change significantly improves performance of static web asset endpoint processing by optimizing JSON serialization and deserialization operations: Key optimizations: - Added reusable List<T> collections to eliminate repeated allocations - Implemented JsonWriterContext for efficient JSON serialization with buffer reuse - Added string interning for well-known header names, selector names, and property values - Introduced direct string property setters to bypass expensive array recreations - Used ArrayPool and stack allocation for UTF-8 encoding buffers - Added optimized PopulateFromMetadataValue methods that populate existing lists Performance improvements (typical): - FromMetadataValue operations: 40-60% faster, 80-90% less memory allocation - ToMetadataValue operations: 5-17% faster with same memory usage - StaticWebAssetEndpointProperty: 56% faster deserialization, 17% faster serialization - StaticWebAssetEndpointResponseHeader: 56% faster deserialization, 15% faster serialization - StaticWebAssetEndpointSelector: 60% faster deserialization, 10% faster serialization These optimizations reduce build-time overhead when processing large numbers of static web assets in ASP.NET Core applications.

Copilot

Pull Request Overview

This PR introduces optimized collection processing for StaticWebAssets serialization and deserialization to reduce memory allocations and improve performance. The changes add new methods for populating existing collections and reuse well-known values during serialization/deserialization.

Key Changes:

Introduces PopulateFromMetadataValue methods that reuse existing collections instead of creating new arrays
Adds string interning for well-known header names, values, selector names, and property names
Implements pooled JSON writers and array buffer writers for reduced allocations

Reviewed Changes

Copilot reviewed 39 out of 40 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs	Adds PopulateFromMetadataValue method and optimized serialization with string interning
src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointSelector.cs	Adds PopulateFromMetadataValue method and optimized serialization for selectors
src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointResponseHeader.cs	Adds PopulateFromMetadataValue method and optimized serialization for response headers
src/StaticWebAssetsSdk/Tasks/Data/WellKnown*.cs	New classes containing interned strings for common values to reduce allocations
src/StaticWebAssetsSdk/Tasks/Utils/JsonWriterContext.cs	Reusable JSON writing context with pooled buffers
test/Microsoft.NET.Sdk.StaticWebAssets.Tests/StaticWebAssets/*Test.cs	Comprehensive test coverage for new functionality
src/StaticWebAssetsSdk/benchmarks/*.cs	Benchmark classes to measure performance improvements

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpoint.cs

MackinnonBuck · 2025-08-11T14:22:23Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+        }
+
+        var result = JsonSerializer.Deserialize(value, _jsonTypeInfo);
+        Array.Sort(result);


Why the sort here? Is the sortedness of the endpoint properties utilized anywhere or is it just for the sake of having a predictable and deterministic ordering?

Predictable deterministic ordering for when we write them into files.

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

MackinnonBuck · 2025-08-11T14:31:35Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+        // Expect to be positioned at start of array
+        if (reader.TokenType != JsonTokenType.StartArray)
+        {
+            reader.Read(); // Move to start array if not already there


Should we assert here that the token type is now JsonTokenType.StartArray after reading?

We could do Debug.Assert here, but that won't help customers as it will be stripped out on Release builds. In general, this is trusted data that we read and write, so we can expect that it's in the right shape.

MackinnonBuck · 2025-08-11T14:43:55Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+        }
+    }
+
+    public static void PopulateFromMetadataValue(ref Utf8JsonReader reader, List<StaticWebAssetEndpointProperty> properties)


Are the performance gains from this method primarily due to the fact that we're reusing the properties list to reduce allocations? Or is it that the STJ source generator doesn't generally produce code as optimized/tailored code?

We save in a bunch of places:

Decoding properties: We skip because we map the utf8 bits to the well-known strings.

Allocations: We reuse the strings everywhere, which makes string comparisons O(1) instead of O(N) (Because equal strings share the same memory address).

Perfect hashing: We don't have to check things on a dictionary or write an list of ifs we can just check for well-known stuff way more efficiently.

MackinnonBuck · 2025-08-11T14:49:15Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+        return JsonSerializer.Serialize(properties, _jsonTypeInfo);
+    }
+
+    internal static string ToMetadataValue(


I see that this yields up to a 17% perf improvement on microbenchmarks. Do you have measurements or predictions on what the impact of this optimization would be on a typical build? Just want to have an idea on what the tradeoff is between performance and maintainability here.

This happens on the main loop of a bunch of Tasks, like DefineStaticWebAssetEndpoints, ApplyCompressionNegotiation, GenerateStaticWebAssetsManifest that happen on incremental builds.

It's hard to predict the results here until we have merged it as we can't compare it against a released SDK (It has been PGOd, which gives it an additional boost).

But in general, anything where we can remove allocations and speed up items going through the main loop should be worth it.

As for maintainability, I had the same concern, but with Copilot it is actually much more straightforward to maintain this code. We can if we want to, add explicit instructions to ensure that it updates these paths.

MackinnonBuck · 2025-08-11T14:50:53Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+    internal static JsonWriterContext CreateWriter()
+    {
+        var context = new JsonWriterContext();
+        return context;
+    }


Why is this helper necessary? Can't the caller just new-up their own JsonWriterContext() directly?

new-ing up a JsonWritterContext is expensive, so it's worth caching

MackinnonBuck · 2025-08-11T15:09:20Z

src/StaticWebAssetsSdk/Tasks/Data/WellKnownResponseHeaderValues.cs

+    /// <returns>The interned header value or null if not well-known</returns>
+    public static string TryGetInternedHeaderValue(ReadOnlySpan<byte> headerValueSpan)
+    {
+        return headerValueSpan.Length switch


This seems like it could be a good application for generated code (e.g., using a T4 template). That way this wouldn't all have to be hard-coded. Although I don't see that kind of thing happening already in this repo. This is good as-is, just a passing thought.

I actually used copilot instead to generate this. Essentially asked it:

Write a minimal perfect hash for matching against these values.

This is essentially faster than having a dictionary and hashing over the string.

javiercn · 2025-08-11T16:30:50Z

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs

+                    var internedName = WellKnownEndpointPropertyNames.TryGetInternedPropertyName(reader.ValueSpan);
+                    property.Name = internedName ?? reader.GetString();


This is where the interning happens

Address feedback Co-authored-by: Copilot <[email protected]>

github-actions bot added the Area-AspNetCore RazorSDK, BlazorWebAssemblySDK, dotnet-watch label Jul 8, 2025

javiercn commented Jul 8, 2025

View reviewed changes

src/StaticWebAssetsSdk/Tasks/Utils/PooledArrayBufferWriter.cs Show resolved Hide resolved

javiercn force-pushed the javiercn/improve-json-allocs branch from 3ab44b5 to bc59fb1 Compare July 8, 2025 16:20

javiercn marked this pull request as ready for review July 8, 2025 22:31

javiercn requested a review from a team as a code owner July 8, 2025 22:31

javiercn force-pushed the javiercn/improve-json-allocs branch 2 times, most recently from 38a718b to 0bbc810 Compare July 8, 2025 22:42

javiercn force-pushed the javiercn/improve-json-allocs branch from 0bbc810 to 67f679f Compare July 8, 2025 22:42

javiercn requested a review from MackinnonBuck July 8, 2025 22:44

Merge branch 'main' into javiercn/improve-json-allocs

539ae62

Copilot AI review requested due to automatic review settings August 9, 2025 19:51

Copilot AI reviewed Aug 9, 2025

View reviewed changes

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointProperty.cs Outdated Show resolved Hide resolved

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpoint.cs Show resolved Hide resolved

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MackinnonBuck reviewed Aug 11, 2025

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javiercn commented Aug 11, 2025

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javiercn and others added 2 commits August 11, 2025 18:46

Apply suggestions from code review

6eeb245

Address feedback Co-authored-by: Copilot <[email protected]>

Merge branch 'main' into javiercn/improve-json-allocs

a35efd6

		var internedName = WellKnownEndpointPropertyNames.TryGetInternedPropertyName(reader.ValueSpan);
		property.Name = internedName ?? reader.GetString();

[StaticWebAssets] Process collection properties with amortized allocation #49682

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[StaticWebAssets] Process collection properties with amortized allocation #49682

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Performance Results by Component

1. StaticWebAssetEndpointProperty Benchmarks

.NET 10.0 Results

.NET Framework 4.8.1 Results

2. StaticWebAssetEndpointResponseHeader Benchmarks

.NET 10.0 Results

.NET Framework 4.8.1 Results

3. StaticWebAssetEndpointSelector Benchmarks

.NET 10.0 Results

.NET Framework 4.8.1 Results

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Pull Request Overview

Key Changes:

Reviewed Changes

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javiercn commented Jul 8, 2025 •

edited

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