Make MemoryCache thread-safety tests deterministic#129897
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The three concurrency tests in MemoryCacheSetAndRemoveTests relied on fixed multi-second delays plus task cancellation to bound their run, which made them slow and racy, so they were disabled. Rewrite them to run a fixed number of iterations per thread, started together with a Barrier, removing all wall-clock timing. OvercapacityPurge_AreThreadSafe also created its tasks with a cancellation token, so cancellation left them Canceled and Task.WaitAll threw TaskCanceledException. AddAndReplaceEntries_AreThreadSafe shared a single Random across threads, which is not thread-safe; each thread now owns its own instance. Re-enable both. GetAndSet_AreThreadSafe_AndUpdatesNeverLeavesNullValues is de-raced too but stays disabled under dotnet#72879, an unrelated cache bug it exercises. Fix dotnet#72890
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The three concurrency tests in
MemoryCacheSetAndRemoveTestswere disabled because they were timing-sensitive and racy. They relied on fixed multi-second delays to bound their run, so every run took ~7s and the outcome depended on thread scheduling. Two of them also had bugs in the test code itself:OvercapacityPurge_AreThreadSafecreated its worker tasks with a cancellation token (Task.Run(..., cts.Token)). When the token fired, the tasks ended up Canceled, soTask.WaitAllthrewTaskCanceledException, the failure tracked in the issue.AddAndReplaceEntries_AreThreadSafeshared a single Random instance across three threads. Random is not thread-safe, so concurrent use corrupted its state.Fix #72890