Why Python Worker Processes Should Never Inherit Parent Logging Handlers

Python's multiprocessing module can cause subtle but serious bugs when worker processes inherit logging handlers from the parent process. Under the fork start method, children copy the parent's RLock mid-emit, potentially deadlocking forever if the lock was held at fork time. Under spawn, children start with a fresh interpreter and never run the parent's logging setup, causing worker logs to silently disappear while the parent reports success. The same logging cleanup code can therefore produce two distinct failures — a deadlock on Linux and silent log loss on Windows or macOS — making cross-platform review unreliable. Developers are advised to treat logging handlers like file descriptors or open sockets: each process should configure its own handlers explicitly rather than relying on inherited state.