Conditionalize thread local cleaning. Possible perf degradation fix

lib/puma/configuration.rb

@@ -212,6 +212,13 @@ module Puma
         @options[:binds] << "tcp://#{Configuration::DefaultTCPHost}:#{port}"
       end
 
+      # Work around leaky apps that leave garbage in Thread locals
+      # across requests
+      #
+      def clean_thread_locals(which=true)
+        @options[:clean_thread_locals] = which
+      end
+
       # Daemonize the server into the background. Highly suggest that
       # this be combined with +pidfile+ and +stdout_redirect+.
       def daemonize(which=true)

lib/puma/server.rb

@@ -259,6 +259,8 @@ module Puma
         end
       end
 
+      @thread_pool.clean_thread_locals = @options[:clean_thread_locals]
+
       @reactor = Reactor.new self, @thread_pool
 
       @reactor.run_in_thread

lib/puma/thread_pool.rb

@@ -36,9 +36,12 @@ module Puma
       @mutex.synchronize do
         @min.times { spawn_thread }
       end
+
+      @clean_thread_locals = false
     end
 
     attr_reader :spawned, :trim_requested
+    attr_accessor :clean_thread_locals
 
     # How many objects have yet to be processed by the pool?
     #
@@ -89,8 +92,10 @@ module Puma
 
           break unless continue
 
-          Thread.current.keys.each do |key|
-            Thread.current[key] = nil unless key == :__recursive_key__
+          if @clean_thread_locals
+            Thread.current.keys.each do |key|
+              Thread.current[key] = nil unless key == :__recursive_key__
+            end
           end
 
           block.call(work, *extra)