Merge pull request #441 from jeremyevans/avoid-unnecessary-thread-pool

Avoid creating an unnecessary thread pool

Author: hsbt

lib/rake/application.rb

@@ -124,7 +124,7 @@ def run_with_threads
 
       yield
 
-      thread_pool.join
+      thread_pool.join if defined?(@thread_pool)
       if options.job_stats
         stats = thread_pool.statistics
         puts "Maximum active threads: #{stats[:max_active_threads]} + main"