perf(dotnet/policy): cache YamlDotNet IDeserializer in Policy.FromYaml#2155
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imran-siddique merged 1 commit intoMay 12, 2026
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DeserializerBuilder.Build() walks every public property on the target type (Policy.PolicyDocument and Policy.RuleDocument), resolves naming conventions, and wires up type inspectors and converters. That cost is identical on every call and the resulting IDeserializer is documented as thread-safe once built, so building one per call is pure waste -- loading a few policies at startup, or hot-reloading them from disk, pays the construction cost N times for no benefit. Promote the builder result to a static-readonly field so every FromYaml / FromYamlFile call reuses the same configured deserializer. This mirrors the existing JsonSerializerOptions caching right above it (PolicyDocument's JSON path already does the equivalent). The new regression test parses three different policy documents sequentially and in parallel across multiple iterations, pinning that the cached deserializer's results stay stable across calls -- guarding against future refactors that would (accidentally) introduce per-call state on the shared instance.
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Verdict: ✅ Ready for human review |
MohammadHaroonAbuomar
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microsoft#2155) DeserializerBuilder.Build() walks every public property on the target type (Policy.PolicyDocument and Policy.RuleDocument), resolves naming conventions, and wires up type inspectors and converters. That cost is identical on every call and the resulting IDeserializer is documented as thread-safe once built, so building one per call is pure waste -- loading a few policies at startup, or hot-reloading them from disk, pays the construction cost N times for no benefit. Promote the builder result to a static-readonly field so every FromYaml / FromYamlFile call reuses the same configured deserializer. This mirrors the existing JsonSerializerOptions caching right above it (PolicyDocument's JSON path already does the equivalent). The new regression test parses three different policy documents sequentially and in parallel across multiple iterations, pinning that the cached deserializer's results stay stable across calls -- guarding against future refactors that would (accidentally) introduce per-call state on the shared instance.
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Summary
Policy.FromYamlrebuilds a freshIDeserializeron every call:DeserializerBuilder.Build()walks every public property on the target type (Policy.PolicyDocumentandPolicy.RuleDocument), resolves the naming convention, and wires up type inspectors and converters. That cost is identical on every call, and YamlDotNet documents the resultingIDeserializeras thread-safe once built -- so building it per call is pure waste. Loading a handful of policies at startup, or hot-reloading them from disk, pays the construction cost N times for no benefit.Change
Promote the builder result to a
static readonly IDeserializerfield so everyFromYaml/FromYamlFilecall reuses the same configured deserializer. This mirrors the existingJsonSerializerOptionscaching right above it -- the JSON path already does the equivalent.Tests
Added
FromYaml_CachedDeserializer_ProducesStableResultsAcrossCalls: parses three different policy documents sequentially and in parallel across multiple iterations, and asserts that field-for-field results stay stable across calls. Guards against future refactors that would accidentally introduce per-call state on the shared instance.Test plan
dotnet test-- 658 / 658 passing (previous baseline 657 + 1 new)FromYaml_*tests unchangedSurfaced during independent audit conducted by @finnoybu (Ken Tannenbaum, AEGIS Initiative); [LOW, .NET].