Set more sensible default threads count (#196)

* Set more sensible default threads count

* Don't care about pre 1.6

* Typo

* add Nothing back into the union

Author: Moelf

src/booster.jl

@@ -108,6 +108,7 @@ function Booster(cache::AbstractVector{<:DMatrix};
                  model_file::AbstractString="",
                  tree_method::Union{Nothing,AbstractString}=nothing,
                  validate_parameters::Bool=true,
+                 nthread=Threads.nthreads(),
                  kw...
                 )
     o = Ref{BoosterHandle}()
@@ -124,7 +125,7 @@ function Booster(cache::AbstractVector{<:DMatrix};
     else
         (tree_method=tree_method,)
     end
-    setparams!(b; validate_parameters, tm..., kw...)
+    setparams!(b; validate_parameters, nthread, tm..., kw...)
     b
 end
 Booster(dm::DMatrix; kw...) = Booster([dm]; kw...)

src/dmatrix.jl

@@ -581,13 +581,13 @@ function _unsafe_dataiter_reset(ptr::Ptr)
 end
 
 function _dmatrix_caching_config_json(;cache_prefix::AbstractString,
-                                      nthreads::Union{Integer,Nothing},
+                                      nthreads::Union{Integer, Nothing},
                                       missing_value::Float32=NaN32,
                                      )
     d = Dict("missing"=>"__NAN_STR__",
              "cache_prefix"=>cache_prefix,
             )
-    isnothing(nthreads) || (d["nthreads"] = nthreads)
+    isnothing(nthreads) || (d["nthreads"] = string(nthreads))
     # this is to strip out the special Float32 values to representations it'll accept
     nanstr = if isnan(missing_value)
         "NaN"
@@ -603,7 +603,7 @@ end
 function DMatrix(itr::DataIterator;
                  missing_value::Float32=NaN32,
                  cache_prefix::AbstractString=joinpath(tempdir(),"xgb-cache"),
-                 nthreads::Union{Integer,Nothing}=nothing,
+                 nthreads::Union{Integer, Nothing}=Threads.nthreads(),
                  kw...
                 )
     o = Ref{DMatrixHandle}()