fix: pgxpool deadlock on context cancellation — release semaphore immediately - #5
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Fixes concurrent context cancellation + semaphore contention causing pool to livelock. Two-part fix: 1. puddle/pool.go acquire(): check ctx.Done() after semaphore acquire to prevent goroutine leak when context is canceled between TryAcquire success and resource creation. 2. pgxpool/pool.go Acquire(): check ctx.Err() between retry iterations so a cancelled context terminates the retry loop immediately instead of cycling through all maxConns attempts. Includes regression test TestPoolAcquireStressCancelContention that exercises high-concurrency acquire with rapid context cancellation.
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Fixes deadlock and goroutine leak in pgxpool.Acquire() on context cancellation.
Root cause: When context is cancelled after TryAcquire succeeds but before resource creation completes, the semaphore is held indefinitely — blocking all future acquires.
Fix: Added ctx.Done() check after TryAcquire succeeds. If context is cancelled, immediately release semaphore and return the context error. Also added ctx.Err() checks in retry loop after Destroy() calls for expired connections.
Test: TestPoolAcquireStressCancelContention — 30 goroutines × 10 attempts with 1-5ms timeouts against saturated pool (MaxSize=3). Verifies pool remains functional and stats are consistent after stress.
Closes #1