Reflection vs. source generation in System.Text.Json #26559

tdykstra · 2021-10-18T22:47:10Z

File Type	File Name	Published Url
Content	docs/standard/serialization/system-text-json-overview.md	https://review.docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-overview?branch=pr-en-us-26559
Content	docs/standard/serialization/system-text-json-source-generation.md	https://review.docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-source-generation?branch=pr-en-us-26559
Content	docs/standard/serialization/system-text-json-source-generation-modes.md	https://review.docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-source-generation-modes?branch=pr-en-us-26559

docs/standard/serialization/system-text-json-source-generation-modes.md

docs/standard/serialization/system-text-json-overview.md

docs/standard/serialization/system-text-json-source-generation-modes.md

gewarren

One small suggestion to consider because it took me a little while to figure out the columns.

docs/standard/serialization/system-text-json-source-generation-modes.md

…-modes.md Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>

tdykstra · 2021-10-21T15:56:57Z

@gewarren Thanks for the review, great suggestions!

layomia

Just a few comments but LGTM

layomia · 2021-11-17T02:26:35Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+
+| Benefit                                              | Reflection | Source generation:<br/>Metadata collection | Source generation:<br/>Serialization optimization |
+|------------------------------------------------------|------------|---------------------|----------------------------|
+| Simpler to code and debug.                           | ✔️        | ❌                  | ❌                        |


In what ways do you find the reflection serializer simpler to code and debug?

layomia · 2021-11-17T02:26:57Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+| Supports non-public accessors.                       | ✔️        | ❌                  | ❌                        |
+| Supports init-only properties.                       | ✔️        | ❌                  | ❌                        |
+| Supports all available serialization customizations. | ✔️        | ❌                  | ❌                        |
+| Reduces start-up time.                               | ❌        | ✔️                  | ❌                        |


Serialization optimization also reduces start-up time.

layomia · 2021-11-17T02:28:24Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+| Simpler to code and debug.                           | ✔️        | ❌                  | ❌                        |
+| Supports non-public accessors.                       | ✔️        | ❌                  | ❌                        |
+| Supports init-only properties.                       | ✔️        | ❌                  | ❌                        |
+| Supports all available serialization customizations. | ✔️        | ❌                  | ❌                        |


I believe metadata collection supports all customizations. Which ones did you find missing?

layomia · 2021-11-17T02:29:22Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+
+By default, `JsonSerializer` collects metadata at run time by using [reflection](../../csharp/programming-guide/concepts/reflection.md). Whenever `JsonSerializer` has to serialize or deserialize a type for the first time, it collects and caches this metadata. The metadata collection process takes time and uses memory.
+
+## Source generation - metadata collection mode


Should this just be "Metadata collection mode"

layomia · 2021-11-17T02:29:52Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+
+The performance improvements provided by source generation can be substantial. For example, [test results](https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/#how-source-generation-provides-benefits) have shown up to 40% or more startup time reduction, private memory reduction, throughput speed increase (in serialization optimization mode), and app size reduction.
+
+## Source generation - known issues


"Serialization optimization mode" should come before this section. Also should it just be "Known issues"?

layomia · 2021-11-17T02:41:29Z

docs/standard/serialization/system-text-json-source-generation-modes.md

+
+You can use source generation to move the metadata collection process from run time to compile time. During compilation, the metadata is collected and source code files are generated. The generated source code files are automatically compiled as an integral part of the application. This compile-time metadata collection eliminates run-time metadata collection, which improves performance of both serialization and deserialization.
+
+The performance improvements provided by source generation can be substantial. For example, [test results](https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/#how-source-generation-provides-benefits) have shown up to 40% or more startup time reduction, private memory reduction, throughput speed increase (in serialization optimization mode), and app size reduction.


I'd avoid quantifying the improvements here and just leave the pointer to the perf section of the blog.

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tdykstra changed the title ~~WIIP: Reflection vs. source generation in System.Text.Json~~ Reflection vs. source generation in System.Text.Json Oct 19, 2021

tdykstra marked this pull request as ready for review October 19, 2021 23:45

tdykstra requested a review from a team as a code owner October 19, 2021 23:45

tdykstra requested review from layomia and adegeo October 19, 2021 23:45

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gewarren reviewed Oct 20, 2021

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tdykstra merged commit 14e8ef2 into dotnet:main Oct 29, 2021

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Reflection vs. source generation in System.Text.Json #26559

Reflection vs. source generation in System.Text.Json #26559

tdykstra commented Oct 18, 2021 •

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		By default, `JsonSerializer` collects metadata at run time by using [reflection](../../csharp/programming-guide/concepts/reflection.md). Whenever `JsonSerializer` has to serialize or deserialize a type for the first time, it collects and caches this metadata. The metadata collection process takes time and uses memory.

		## Source generation - metadata collection mode


		The performance improvements provided by source generation can be substantial. For example, [test results](https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/#how-source-generation-provides-benefits) have shown up to 40% or more startup time reduction, private memory reduction, throughput speed increase (in serialization optimization mode), and app size reduction.

		## Source generation - known issues


		You can use source generation to move the metadata collection process from run time to compile time. During compilation, the metadata is collected and source code files are generated. The generated source code files are automatically compiled as an integral part of the application. This compile-time metadata collection eliminates run-time metadata collection, which improves performance of both serialization and deserialization.

		The performance improvements provided by source generation can be substantial. For example, [test results](https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/#how-source-generation-provides-benefits) have shown up to 40% or more startup time reduction, private memory reduction, throughput speed increase (in serialization optimization mode), and app size reduction.

Reflection vs. source generation in System.Text.Json #26559

Reflection vs. source generation in System.Text.Json #26559

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tdykstra commented Oct 18, 2021 •

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