AnyIO's process-pool workers have a vulnerability where stderr is connected to a pipe that is never drained. This can cause the pipe to fill and block indefinitely if the worker writes enough data to stderr, leading to a deadlock. The issue affects versions from 0.13.1 up to but not including 0.32. A fix is available in version 0.32. Closing sys.stderr in the target function can serve as a workaround to prevent deadlock.