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Hand a dropping meter's block back under the registry lock - #13
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PR #11's CI run refused work that fitted once in two hundred rounds of many_meters_racing_for_the_last_of_a_budget_that_exactly_fits, on code that passed the same test twice before on CI and 360 times locally. release_meter emptied the balance and refunded it before taking the registry, so for the moment between those two steps a dropping meter's unspent block was in no balance and still in the counter, outside any lock. A meter refused in that moment could not reclaim it. The hand-back now happens under the exclusive hold, with the deregistration. A new contract test makes fifteen threads create, charge and drop meters continuously while one spends the budget down: 9 of 30 release runs failed before this change, 0 of 120 after, and 0 of 150 for the three racing tests with every core of the host saturated by other work. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Documentation only. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Fixes a spurious
BudgetExceededthat PR #11's CI run hit once in two hundred rounds ofmany_meters_racing_for_the_last_of_a_budget_that_exactly_fits. The defect is onmain, from my own exclusion fix in #10 (cec897f), which covered admission and refusal and missed the drop.Cause.
release_meteremptied the meter's balance and refunded it, and only then took the registry lock to deregister. Between the two steps the dropping meter's unspent block was in no balance and still in the shared counter, under no lock. A refusal is exact only if every admitted, unspent unit can be found, and in that moment one could not.Fix. Take the registry exclusively first; empty, refund and deregister under it. I re-audited every transition that moves units between the counter and a balance; this was the only one outside the lock.
Test.
a_meter_dropping_its_block_does_not_hide_it_from_a_refusal: fifteen threads create, charge and drop meters continuously while one spends down a budget equal to all the work. Onmain: 9 of 30 release runs fail. With the fix: 0 of 120, and 0 of 150 for the three existing racing tests with all cores saturated by other processes, which is the condition a CI runner is in and this laptop normally is not.🤖 Generated with Claude Code