devel/rlog 1.4 MidnightBSD

RLog provides a flexible message logging facility for C++ programs and libraries. It is subscription based, meaning you can subscribe to messages of your choice in an number of ways: by hierarchical channel name (e.g. "debug", "debug/ special", "error", etc.), or file name, component name, etc. Log messages are individually enabled. It is meant to be fast enough to leave in production code - even where it may be called many times, as both the GCC and Intel compilers reduce the logging overhead a few clock cycles if they are dormant (with no subscribers). Other add-on components can extend subscriptions to external programs, allowing you to enable and collect debugging messages remotely.

See also: https://github.com/anastmag/rlog