default.mspec: limit cores

* spec/default.mspec (MSpecScript::JobServer#cores): limit max
  number of processors, not to acquire tokens more than necessary.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59103 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/default.mspec

@@ -24,15 +24,16 @@ class MSpecScript
 end
 
 module MSpecScript::JobServer
-  def cores
-    if /(?:\A|\s)--jobserver-(?:auth|fds)=(\d+),(\d+)/ =~ ENV["MAKEFLAGS"]
-      cores = 0
+  def cores(max = 1)
+    if max > 1 and /(?:\A|\s)--jobserver-(?:auth|fds)=(\d+),(\d+)/ =~ ENV["MAKEFLAGS"]
+      cores = 1
       begin
         r = IO.for_fd($1.to_i(10), "rb", autoclose: false)
         w = IO.for_fd($2.to_i(10), "wb", autoclose: false)
-        jobtokens = r.read_nonblock(1024)
+        jobtokens = r.read_nonblock(max - 1)
         cores = jobtokens.size
         if cores > 0
+          cores += 1
           jobserver = w
           w = nil
           at_exit {

spec/mspec/lib/mspec/commands/mspec.rb

@@ -98,7 +98,7 @@ class MSpecMain < MSpecScript
     end
 
     output_files = []
-    processes = [cores, @files.size].min
+    processes = cores(@files.size)
     children = processes.times.map { |i|
       name = tmp "mspec-multi-#{i}"
       output_files << name

spec/mspec/lib/mspec/utils/script.rb

@@ -234,9 +234,9 @@ class MSpecScript
     files patterns
   end
 
-  def cores
+  def cores(max = 1)
     require 'etc'
-    Etc.nprocessors
+    [Etc.nprocessors, max].min
   end
 
   def setup_env