BloombergLP::ball::LoggerManager::registerObserver

Add the specified observer with the specified observerName to the registry of observers maintained by this logger manager. Return 0 if observer was successfully registered with this logger manager, and a non‐zero value (with no effect) otherwise. Henceforth, all log records published by this logger manager are published to this observer, until observer is deregistered. The behavior is undefined if a cyclic reference is created among registered observers. Note that this method will fail if an observer having observerName is already registered.