Document NullabilityInfoContext thread-safety constraints

[Copilot]

NullabilityInfoContext uses a non-concurrent dictionary for internal caching, causing InvalidOperationException when Create methods are called concurrently. This wasn't documented anywhere. See dotnet/runtime#100254 for the concurrency failure.

Changes:

• Added <threadsafe> section to type documentation specifying non-thread-safe behavior and recommending external synchronization for multi-threaded scenarios
• Added <threadsafe> sections to each of the four Create method overloads (EventInfo, FieldInfo, ParameterInfo, PropertyInfo) stating "This method is not thread safe"
• Uses "thread safe" (without hyphen) consistently with other System.Reflection types

Context:

// This throws InvalidOperationException
var ctx = new NullabilityInfoContext();
Parallel.ForEach(properties, prop => ctx.Create(prop));

// Use external synchronization for multi-threaded scenarios
var ctx = new NullabilityInfoContext();
var lockObj = new object();
Parallel.ForEach(properties, prop => {
    lock (lockObj) {
        var info = ctx.Create(prop);
    }
});

Original prompt

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This section details on the original issue you should resolve

<issue_title>Not thread-safety should be explicitly documented.</issue_title>
<issue_description>### Type of issue

Missing information

Description

I believe this issue contains some valuable details which deserve presence in the documentation or even in xmldoc comments of the Create method.

Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.reflection.nullabilityinfocontext.create?view=net-10.0

Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Reflection/NullabilityInfoContext.xml

Document Version Independent Id

a6845bae-0825-8996-cbfe-71285933a25a

Platform Id

847cd8f7-3db2-2288-932d-b1aeea925814

Article author

@dotnet-bot</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Not thread-safety should be explicitly documented. #12261

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[Copilot]

Pull request overview

Documents the thread-safety limitations of System.Reflection.NullabilityInfoContext, clarifying that concurrent calls to Create can fail due to internal non-concurrent caching.

Changes:

• Added a <threadsafe> section to the NullabilityInfoContext type docs describing non-thread-safe behavior and recommended mitigations.
• Added non-thread-safe warnings to the <remarks> of the four Create overloads (EventInfo, FieldInfo, ParameterInfo, PropertyInfo).

[BillWagner]

This LGTM