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VSTHRD116 Use ThreadStaticAttribute only with static fields

ThreadStaticAttribute has no effect when applied to an instance field. Each object already has its own instance field, and the runtime does not create a separate value for each thread.

Examples of patterns that are flagged by this analyzer

class Example
{
    [ThreadStatic]
    private object value;
}

Class Example
    <ThreadStatic>
    Private value As Object
End Class

Solution

If the value should be shared by all threads for each object, remove ThreadStaticAttribute. If each thread should have its own value, make the field static after confirming that changing it from per-instance state is appropriate.

class Example
{
    [ThreadStatic]
    private static object value;
}

Class Example
    <ThreadStatic>
    Private Shared value As Object
End Class

No code fix is offered because removing the attribute and making the field static have different semantics.

This rule is equivalent to .NET SDK rule CA2259. When both analyzer packages are enabled, configure or suppress one of the duplicate diagnostics.

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