Seed ThreadLocalRandom from a cryptographic source - #8377
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Aaronontheweb merged 3 commits intoJul 16, 2026
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TickCount-based seeding gives simultaneously-started processes correlated per-thread random streams, affecting gossip target selection, backoff/circuit-breaker jitter, and shuffles. This was observed as identical system UIDs across MNTR node processes.
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Deep review found the original regression test did not exercise the reported cross-process defect: two threads in one process already received distinct Interlocked-incremented seeds before this change, and the array comparison did not provide useful coverage of the seed source. Commit 5d95348 isolates the cryptographic seed draw, tests that repeated draws do not collapse to TickCount-style deterministic behavior, makes the ThreadLocal field readonly, and removes the inaccurate claim that random collisions are impossible. Focused result: 2/2 passed; Akka warnings-as-errors build clean. |
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LGTM, we should probably replace ThreadLocalRandom with Random.Shared in the near future anyway.
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* Seed ThreadLocalRandom from a cryptographic source TickCount-based seeding gives simultaneously-started processes correlated per-thread random streams, affecting gossip target selection, backoff/circuit-breaker jitter, and shuffles. This was observed as identical system UIDs across MNTR node processes. * Harden ThreadLocalRandom seed regression coverage (cherry picked from commit 86fdbb3)
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* Seed ThreadLocalRandom from a cryptographic source TickCount-based seeding gives simultaneously-started processes correlated per-thread random streams, affecting gossip target selection, backoff/circuit-breaker jitter, and shuffles. This was observed as identical system UIDs across MNTR node processes. * Harden ThreadLocalRandom seed regression coverage (cherry picked from commit 86fdbb3)
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Summary
ThreadLocalRandomseeded its per-thread base fromEnvironment.TickCount. Processes started in the same millisecond (orchestrator-launched cluster nodes, MNTR node processes) share that base, so corresponding threads across those processes draw identical random streams. This has already manifested as identical system UIDs across MNTR node processes.Replaces the
TickCountbase with a base drawn fromRandomNumberGenerator.GetInt32. The per-threadInterlocked.Incrementscheme is unchanged; only the shared base is now cryptographically random. Public API is unchanged.Test plan
dotnet build src/core/Akka -warnaserror- cleandotnet test src/core/Akka.Tests --filter FullyQualifiedName~Akka.Tests.Utilx3 - 91/91 passing each rundotnet test src/core/Akka.API.Tests --filter FullyQualifiedName~ApproveCore- zero API churn