Add maxlog example

[ericphanson]

I found it useful, and am using this code in https://github.com/beacon-biosignals/BeaconK8sUtilities.jl/pull/14

[ericphanson]

Ah, the way Base does this is it keeps a dictionary of counts of remaining times to emit the log, instead of count of logs emitted. Then in shouldlog it can just check that, so it only needs the id and not maxlog. Then later in handle_message it populates the dict with maxlog info. (Example: JuliaLang/julia#43641). So they are basically doing it as an EarlyFilteredLogger instead of ActiveFilteredLogger IIUC, in terms of when the filtering happens.

However, I don't really know how to do that in the LoggingExtras framework. It seems we'd need to share state between an EarlyFilteredLogger and a TransformerLogger, or something like that.

edit: ah, but that can probably just be done with a closure!

[ericphanson]

I think

function make_maxlog_logger(logger)
    counts_remaining = Dict{Any,Int}()
    A = ActiveFilteredLogger(logger) do log
        maxlog = get(log.kwargs, :maxlog, nothing)
        if maxlog isa Integer
            remaining = get!(counts_remaining, log.id, Int(maxlog)::Int)
            counts_remaining[log.id] = remaining-1
            return remaining > 0
        else
            return true
        end
    end
   return EarlyFilteredLogger(A) do log
        return get(counts_remaining, log.id, 1) > 0
    end
end

is basically what Base is doing. Should I update the example? I'm not totally sure how much of a difference it makes; we can early exit from maxlogs at the cost of doing an extra layer of loggers to check.

[fredrikekre]

That definitely isn't as clean as the example we merged, which is a shame.

[fredrikekre]

Maybe both options can be added to https://julialogging.github.io/ in a "how to throttle messages" section or something like that, and then the complicated example can be included too.