Resource Leak

Files, sockets, subscriptions, or other finite resources are acquired without a guaranteed release path.

A resource is opened but not closed. Under low load the process recycles or the OS cleans up on exit, so the bug stays hidden. Under real load, file-descriptor exhaustion, memory bloat, or orphaned connections appear and cascade.

Symptoms

• open(...) without a matching close() or with block.
• Database connections or HTTP clients instantiated per-request without pooling or teardown.
• Event listeners / observers / subscriptions registered but never removed.
• Background tasks or timers spawned without cancellation paths.
• Gradual memory growth that correlates with request count.

What to do

• Pair every acquire with a release. Use language constructs that guarantee teardown: with (Python), using / try-with-resources (C#/Java), defer (Go), try/finally (JS/TS).
• For resources that outlive a single function, document ownership: who closes it, when, on which code path — including error paths.
• Prefer pooled clients (HTTP, database) over creating a new one per call.
• When registering event listeners, return the unregister function in the same scope so the caller can clean up.
• Test the teardown path. Kill a process or trigger an error mid-operation and confirm resources are released.