use max Etc.nprocessors processes at a time

lib/jekyll/polyglot/patches/jekyll/site.rb

@@ -1,3 +1,5 @@
+require 'etc'
+
 include Process
 module Jekyll
   class Site
@@ -31,22 +33,27 @@ def process
       prepare
       all_langs = (@languages + [@default_lang]).uniq
       if @parallel_localization
+        nproc = Etc.nprocessors
         pids = {}
-        all_langs.each do |lang|
-          pids[lang] = fork do
-            process_language lang
+        begin
+          all_langs.each do |lang|
+            pids[lang] = fork do
+              process_language lang
+            end
+            while pids.length >= (lang == all_langs[-1] ? 1 : nproc)
+              sleep 0.1
+              pids.map do |lang, pid|
+                pids.delete lang if waitpid pid, Process::WNOHANG
+              end
+            end
           end
-        end
-        Signal.trap('INT') do
+        rescue Interrupt
           all_langs.each do |lang|
+            next unless pids.key? lang
             puts "Killing #{pids[lang]} : #{lang}"
             kill('INT', pids[lang])
           end
         end
-        all_langs.each do |lang|
-          waitpid pids[lang]
-          detach pids[lang]
-        end
       else
         all_langs.each do |lang|
           process_language lang

spec/jekyll/polyglot/patches/jekyll/site_spec.rb

@@ -232,6 +232,18 @@
     end
   end
 
+  describe @site do
+    it 'should spawn no more than Etc.nprocessors processes' do
+      forks = 0
+      allow(Etc).to receive(:nprocessors).and_return(2)
+      allow(@site).to receive(:fork) { forks += 1; fork { sleep 2 } }
+      thr = Thread.new { sleep 1; forks }
+      @site.process
+      expect(thr.value).to eq(Etc.nprocessors)
+      expect(forks).to eq((@langs + [@default_lang]).uniq.length)
+    end
+  end
+
   # describe @relativize_urls do
   #   it 'does not raise' do
   #     expect(@relativize_urls(@site.Document.new(), @relative_url_regex)).not_to raise_error