Madsim v0.8.2#4
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Cherry-pick of transact-rs#4289 onto the madsim v0.8.2 branch. PoolInner::release() published a returned connection (push to the idle queue + release its semaphore permit, which wakes waiters) before incrementing num_idle. A concurrent pop_idle could pop that connection and decrement num_idle while it was still 0, wrapping the usize to usize::MAX. The maintenance task's `for _ in 0..num_idle()` sweep then spins ~forever inside a single non-yielding poll, pegging a worker; on a single-connection pool one of its add_permits handoffs strands the permit on a waiter parked in the spinning worker's LIFO slot, permanently wedging the pool (RisingWave meta silent hang, risingwavelabs/risingwave#24991; upstream report transact-rs#3645). Three-layer fix, each independently sufficient: 1. release(): increment num_idle before publishing the connection, so the counter provably never goes below 0 (subs <= pops <= pushes <= adds) and never exceeds max_connections. 2. pop_idle(): saturating decrement, so even a future ordering bug can only over-count, never wrap. 3. maintenance sweep: cap iterations at max_connections. Includes a 12-thread stress test over the real try_acquire/release paths (fails in <1s with observed=usize::MAX before the fix). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
fix(pool): prevent num_idle underflow that wedges the maintenance task
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Does your PR solve an issue?
DO NOT MERGE.
This PR just displays the patch diffs required for madsim.
We provide a patch of sqlx, v0.8.2
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