I haven't tested it yet, but have two questions anyway:
1. I did not see any reference to the use of Clock.currTime(), which on the last round accounted for about 90% of the total time spent in a log call. Reference: https://issues.dlang.org/show_bug.cgi?id=13433 . (This is the difference between logging-and-filtering ~100k logs/sec and ~1M logs/sec for loggers that use criteria other than logLevel for filtering messages.) Same question for this cycle: Does std.logger API need a method for clients or subclasses to change/defer/omit the call to Clock.currTime? Or defer for a change in std.datetime?
2. We have Tid in the API. What about Fiber and Thread? If we can only pick one, I would vote for Thread rather than Tid, as Tid's currently have no way to be uniquely identified in a logging message. Reference: https://issues.dlang.org/show_bug.cgi?id=6989
General comment: very nice to see continued progress!
