make _min_enabled_level Threads.Atomic

Author: IanButterworth

base/logging/logging.jl

@@ -128,10 +128,12 @@ end
 
 LogLevel(level::LogLevel) = level
 
+isless(a::Int32, b::LogLevel) = isless(a, b.level)
 isless(a::LogLevel, b::LogLevel) = isless(a.level, b.level)
 +(level::LogLevel, inc::Integer) = LogLevel(level.level+inc)
 -(level::LogLevel, inc::Integer) = LogLevel(level.level-inc)
 convert(::Type{LogLevel}, level::Integer) = LogLevel(level)
+convert(::Type{Int32}, level::LogLevel) = level.level
 
 """
     BelowMinLevel
@@ -171,7 +173,7 @@ Alias for [`LogLevel(1_000_001)`](@ref LogLevel).
 const AboveMaxLevel = LogLevel( 1000001)
 
 # Global log limiting mechanism for super fast but inflexible global log limiting.
-const _min_enabled_level = Ref{LogLevel}(Debug)
+const _min_enabled_level = Threads.Atomic{Int32}(Debug)
 
 function show(io::IO, level::LogLevel)
     if     level == BelowMinLevel  print(io, "BelowMinLevel")