[efficiency-improver] Make Jsonite JsonWriter's type-dispatch table static (avoid per-call Dictionary+closures)

The change is in src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonWriter.cs, with coverage in test/UnitTests/Microsoft.Testing.Platform.UnitTests/ServerMode/JsoniteTests.cs. Review the existing branch and patch, then run the listed build and server-mode tests; done means the build passes and serialization behavior remains unchanged without per-call dispatch-table allocation.

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The original pull request description is below.

Goal and rationale

Jsonite.JsonWriter — the JSON serializer used on the net462/netstandard2.0 server-mode code path — rebuilt an 18-entry Dictionary<Type, Action<object>>, with 18 closures each capturing the per-call TextWriter, inside its constructor on every single Serialize() call. This code runs on every RPC message and test-node update sent by a server-mode host running on .NET Framework (e.g. classic MSTest test projects talking JSON-RPC to an IDE or dotnet test), so the wasted allocation scales with test count.

Focus area

Code-Level Efficiency — redundant per-call allocation of a dispatch table that has no per-instance state and can be built once.

Approach

Hoisted the dispatch table to a private static readonly Dictionary<Type, Action<JsonWriter, object>>, using delegates that take the owning JsonWriter as an explicit first parameter (instead of capturing writer/this in a closure per instance). The instance-scoped WriteString calls now go through w.WriteString(...). No behavior change: the table is populated once per process and shared across all JsonWriter instances/calls.

Energy efficiency evidence

Proxy metrics used: wall-clock execution time and GC.GetAllocatedBytesForCurrentThread() (CPU time and memory allocation are both direct proxies for energy: fewer CPU cycles and less GC/DRAM churn per call).

Benchmarked using the actual repository source (Jsonite/*.cs copied into a standalone console harness, !NETCOREAPP forced so the changed code path runs), serializing a small mix of representative values (string, int, double, bool, Guid, DateTime) 200,000 times:

I also verified serialization output is byte-for-byte identical before/after for DateTimeOffset, an anonymous object, an int[] array, a string with escapes, a long, and a float, using the same standalone harness.

Green Software Foundation context

• Energy Proportionality: the fix removes work that scaled with call count but had zero per-call variability in its result — the dispatch table is process-invariant, so building it once instead of once-per-call makes resource use proportional to actual demand (unique types encountered), not call volume.
• Hardware Efficiency: fewer heap allocations mean less GC pressure and better cache locality per call, reducing CPU cycles per RPC message.

Trade-offs

None of note. Delegates now take an extra JsonWriter parameter instead of closing over instance fields, which is a standard pattern for static dispatch tables and does not reduce readability — the intent ("static, allocation-free per-type dispatch") is documented in a comment above the field.

Reproducibility

# Build to confirm the netstandard2.0/net462-only code path still compiles:
./build.sh
.dotnet/dotnet build src/Platform/Microsoft.Testing.Platform -c Debug -f netstandard2.0 --no-restore

# Run the .NET-hosted server-mode tests (System.Text.Json path, unaffected but confirms no regression):
.dotnet/dotnet build test/UnitTests/Microsoft.Testing.Platform.UnitTests -c Debug -f net8.0 --no-restore
artifacts/bin/Microsoft.Testing.Platform.UnitTests/Debug/net8.0/Microsoft.Testing.Platform.UnitTests --filter "FullyQualifiedName~ServerMode"

The Jsonite-specific test file (test/UnitTests/Microsoft.Testing.Platform.UnitTests/ServerMode/JsoniteTests.cs) is net462-only and only compiles on Windows CI (net462 is conditional on $(OS) == 'Windows_NT' and this sandbox is Linux), so it could not be run directly here. I validated correctness by copying the actual Jsonite/*.cs sources (old vs. new) into a standalone console harness with !NETCOREAPP forced, compiling and running both versions, and diffing their output for representative values — all outputs matched exactly.

Test Status

• ./build.sh (full repo restore + build, all target frameworks including netstandard2.0/net462): 0 warnings, 0 errors.
• dotnet format whitespace TestFx.slnx --verify-no-changes --include <file>: clean (after restoring the file's UTF-8 BOM per repo convention).
• Microsoft.Testing.Platform.UnitTests (net8.0, full suite): 2564 passed, 0 failed, 21 skipped (pre-existing skips).
• Microsoft.Testing.Platform.ServerMode.Client.Sources.UnitTests (net8.0, full suite): 105 passed, 0 failed, 2 skipped (pre-existing skips).
• JsoniteTests.cs (net462-only, Windows-only in CI): not runnable in this Linux sandbox; behavior equivalence independently verified via the standalone harness described above.

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From f6c7170a408f66a3ed94a21cf97c5ddd36aae9d3 Mon Sep 17 00:00:00 2001
X-GH-AW-Base-Commit: acf0a077f37c1a4c23500f05fb6f90c526694c3f
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Thu, 24 Sep 2026 22:03:58 +0000
Subject: [PATCH] Make Jsonite JsonWriter's type-dispatch table static

Jsonite.JsonWriter (the JSON serializer used on the net462/netstandard2.0
server-mode code path) rebuilt an 18-entry Dictionary<Type, Action<object>>,
with 18 closures each capturing the per-call TextWriter, inside its
constructor on every single Serialize() call. This runs on every RPC message
and test-node update sent by a server-mode host running on .NET Framework.

Hoist the dispatch table to a static readonly field keyed by delegates that
take the owning JsonWriter as an explicit first parameter, so no per-call
allocation or closure capture is needed. Serialization output is unchanged
(verified via a standalone harness compiling the actual repo source with the
!NETCOREAPP path forced, comparing old vs. new output byte-for-byte for
strings, numbers, Guid, DateTime(Offset), arrays, and objects).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../JsonRpc/Json/Jsonite/JsonWriter.cs        | 65 ++++++++++---------
 1 file changed, 36 insertions(+), 29 deletions(-)

diff --git a/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonWriter.cs b/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonWriter.cs
index 6a77ebc..f5bed06 100644
--- a/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonWriter.cs
+++ b/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonWriter.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 // Copyright(c) 2016, Alexa
... (truncated)

[!WARNING]

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To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
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