Sample
nimble_pool 1.1.0: Check a resource out of a NimblePool and survive the failure paths: what the checkout function must return, which failures the pool recovers from, and which one silently leaks a worker
Verified sample for hex nimble_pool 1.1.0: Check a resource out of a NimblePool and survive the failure paths: what the checkout function must return, which…
sha256:b9a321085b5992dc0c641045e8b697e67dbb23c7f9958ea2d4e0b145d1a2f486
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MIT-0
Execution evidence
The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.
- Evidence basis
- Signed contract pass
- Verification receipts
- 1
- Signing keys that built it
- 1
Declared environment
elixir 1 linux x64 elixir 1 elixir mix
Verification-run environments
| Environment | Contract | Stages | Run |
|---|---|---|---|
| elixir 1 · linux alpine/x64 · docker ed25519:a2ec939a4c60e243 | PASS | compile:PASS · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · hex@1 |
2026-08-14 |
Case
HOW- Goal
- Check a resource out of a NimblePool and survive the failure paths: what the checkout function must return, which failures the pool recovers from, and which one silently leaks a worker
- Packages
- Symbols
-
- NimblePool.start_link
- NimblePool.checkout!
- NimblePool.update
- NimblePool.child_spec
- NimblePool.init_pool
- NimblePool.init_worker
- NimblePool.handle_checkout
- NimblePool.handle_checkin
- NimblePool.handle_update
- NimblePool.handle_cancelled
- NimblePool.terminate_worker
- Environment
- elixir 1
- Created
- 2026-08-14T20:12:13Z
Contract
- assert :pool_size defaults to 10 rather than System.schedulers_online(), by counting exactly ten init_worker callbacks at start_link and no eleventh
- assert lazy: true starts no workers at all and builds exactly one on the first checkout
- assert the checkout! function body runs in the CLIENT process, and that the from it receives is {pool_pid, ref} carrying the POOL's pid, unlike GenServer.handle_call/3 where from carries the caller's
- assert checkout! returns the first element of the two-tuple and only handle_checkin/4 ever sees the second
- assert the asynchronous check-in does not race a re-checkout: twenty-five sequential checkouts against a one-worker pool all succeed
- assert raising inside the checkout! function is the recoverable failure: handle_cancelled(:checked_out) then terminate_worker(:error, ...) then a replacement init_worker, with handle_checkin skipped
- assert returning a value that is not a two-tuple raises {:try_clause, value} and silently leaks the worker: no handle_cancelled, no terminate_worker, no replacement, and every later checkout on that pool exits :timeout
- assert the leaked worker is reclaimed only when the calling process itself dies, which is when the pool's monitor fires handle_cancelled(:checked_out) and terminate_worker(:DOWN, ...)
- assert {:skip, exception, pool_state} from handle_checkout/4 raises that exception in the client while leaving the worker checked in and serving the next call, terminating nothing
- assert {:remove, reason, pool_state} from handle_checkout/4 retries the same checkout against another worker, so a remove keyed on the command destroys and rebuilds more workers than the pool size and the caller only ever sees its own checkout timeout
- assert a caller that times out while still queued cancels as :queued and tears down nothing, while a caller killed holding a worker cancels as :checked_out with terminate_worker reason :DOWN
- assert NimblePool.update/2 is called from inside the checkout! function with from, routes to handle_update/3, and replaces the worker_state that handle_checkin/4 later receives while the client_state passes through unchanged
Files
- csx.json
- lib/csx_nimble_pool/churn_worker.ex
- lib/csx_nimble_pool/instrumented_worker.ex
- mix.exs
- mix.lock
- test/contract_test.exs
- test/test_helper.exs