.NET: Simplify ClientHeadersScope to rely on AsyncLocal natural restoration - #5676
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Roger Barreto (rogerbarreto) merged 4 commits intoMay 11, 2026
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Wesley pointed out (with a clean demo) that AsyncLocal<T> mutations made
inside an awaited async method do not leak back to the caller after the
method returns - the runtime restores the caller's view automatically.
ClientHeadersAgent.RunCoreAsync and RunCoreStreamingAsync are the only
callers of the scope, both are async methods awaited by their callers,
so the explicit using/Dispose pattern was doing work the runtime already
does for us.
* ClientHeadersScope collapsed to a single Current { get; set; } property
over an AsyncLocal<IReadOnlyDictionary<string,string>?>. Drops Push,
the Scope struct, and Dispose. XML doc explains the AsyncLocal natural-
restoration semantics so the design intent is self-documenting.
* ClientHeadersAgent uses a direct ClientHeadersScope.Current = snapshot
before delegating. Drops the local RunAsyncCoreAsync helper and the
snapshot-passed-as-parameter dance.
* Test 10 renamed to ClientHeadersScope_IsAsyncLocalIsolatedAndAutoRestoresAsync;
drops the LIFO claim, keeps the parallel-isolation assertion, and adds
a Wesley-style 'set inside async, caller sees null on return' assertion.
* Test 12 switches from using ClientHeadersScope.Push to direct
Current = ... with try/finally for test isolation.
Snapshot deep-copy in TrySnapshot stays - it defends against caller
mutating the source Dictionary mid-run, which is independent of the
AsyncLocal restoration mechanism.
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Peter Ibekwe (peibekwe)
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westey (westey-m)
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Closes #6003
.NET: Simplify ClientHeadersScope to rely on AsyncLocal natural restoration