Fix evictable cache invalidation race condition #22302
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losipiuk
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losipiuk
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Before the change the following race was possible between threads A, B, C: - A calls invalidate(K) - A increments: invalidations++ - B changes state to be cached, and therefore calls invalidate(K) too - B increments: invalidations++ - C calls get(K) - C reads invalidations counter - C retrieves current token T for key K - C reads value V for T from cache - A reads and removes token T (same) for key K - B attempts to read and remove token for key K, not found - B exits invalidate(K) - C checks invalidations counter (didn't check) - C revives, i.e. re-inserts token T for key K - B calls get(K) - B retrieves token T (same) for key K - B reads value V for T from cache -- despite B having called invalidate(K) At least in this situation the problem is transient. Thread A will momentarily invalidate dataCache for token T, completing the invalidation. This commit fixes this. The bug was introduced by token reviving (commit 17faae3). This commit reverts that one and provides a different solution to the problem that commit was solving.
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Before the change the following race was possible between threads A, B, C:
At least in this situation the problem is transient. Thread A will momentarily invalidate dataCache for token T, completing the invalidation.
This commit fixes this. The bug was introduced by token reviving (commit 17faae3). This commit reverts that one and provides a different solution to the problem that commit was solving.
Fixes #22285
Release notes
(x) Release notes are required -- this fixes correctness problems in a couple different connectors.