fix race condition for FirstLimiter #1101
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| @@ -193,7 +193,7 @@ private void add(String s) { | |||
| // Lock to keep hashmap consistent with counter for remaining | |||
| lock.lock(); | |||
| try { | |||
| if (remaining.get() > 0) { | |||
| if (remaining.get() > 0 && !values.containsKey(s)) { | |||
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This can just check if values.put(s, s) == null. That way it avoids a second operation on the map in the case it is successful.
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ah good point, will update.
Updates the logic to only decrement the remaining counter if an entry was successfully added.
brharrington
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brharrington
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Jan 2, 2024
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Description
Under contention the
CardinalityLimiters.FirstLimiterwill stop accepting values before its limit has been reached.This behavior happens when more than one thread add the same value to the limiter value registry and the
remainingproperty is decremented even though no new entry has been added.Steps to reproduce
I added a test in
CardinalityLimitersConcurrencyTestthat reproduces the issue fairly consistently. It simulates threads submitting the same series of numbers and expect all numbers to be registered. A failing test example output is below, note the--others--entries that should not be present.Fix proposal
After acquiring the lock, we can check if the limiter value registry contains the key before inserting the entry and decrementing
remaining.