I used a system where log messages were assigned arbitrary tags which were themselves strings. The communications subsystem got the "COM" tag, the memory manager got the "MM" tag, etc. Log levels were just tags ("ERROR", "FATAL", etc). The system supported 32 output channels, each channel was associated with some output stream (file, pipe, etc) and each had a Boolean expression which filtered what went to the channel ("FATAL" or "ERROR" or "ALERT" and "MM" or "COM"). A channel could also be assigned a "lifetime" so that output to the channel only lasted for some period of time. Each channel could be setup as the daemon was running so it was easy to start debug messages going to a particular console, memory manager messages to a file, alerts to a pager app., etc. It was great when remote accessing a running system and diagnosing a client's issue. When you are all done you just shutdown the channel or let the channel expire. End of output and no more wasted I/O.