Fix connection race in concurrent GetLastTimeStamp#387
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SimonCropp merged 2 commits intomainfrom Apr 21, 2026
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Commit d9016cc cached ResolveQuery's Task via Interlocked.CompareExchange so concurrent callers would share a single query. But each caller that lost the CompareExchange race still had its own ResolveQuery task running in the background, executing Open/HasViewServerState/Close against the caller's own connection. Meanwhile the caller proceeded to Execute against that same connection, producing "The connection is closed" (production) or "does not support MultipleActiveResultSets" (local) errors. Serialize ResolveQuery with a SemaphoreSlim so at most one caller ever runs it. Strengthen ConcurrencyTests to use closed connections, a synchronous barrier on dedicated threads, and 20 iterations — reliably reproduces the race on the old code.
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Commit d9016cc cached ResolveQuery's Task via Interlocked.CompareExchange
so concurrent callers would share a single query. But each caller that
lost the CompareExchange race still had its own ResolveQuery task running
in the background, executing Open/HasViewServerState/Close against the
caller's own connection. Meanwhile the caller proceeded to Execute against
that same connection, producing "The connection is closed" (production)
or "does not support MultipleActiveResultSets" (local) errors.
Serialize ResolveQuery with a SemaphoreSlim so at most one caller ever
runs it. Strengthen ConcurrencyTests to use closed connections, a
synchronous barrier on dedicated threads, and 20 iterations — reliably
reproduces the race on the old code.