Test adding connection to Reactor after shutdown [changelog skip] (#2418)

* Test adding connection to Reactor after shutdown
Modifies `TestPumaServer#shutdown_requests` to pause `Reactor#add` until after
shutdown begins, to ensure requests are handled correctly for this edge case.
Adds unit-test coverage for the fix introduced in #2377 and updated in #2279.

* Fix Queue#close implementation for Ruby 2.2
Allow `ClosedQueueError` to be raised when `Queue#<<` is called.

* Pass `@block` directly instead of `@block.method(:call)`

lib/puma/queue_close.rb

@@ -18,6 +18,7 @@ unless Queue.instance_methods.include?(:close)
         raise ClosedQueueError if @closed
         super
       end
+      alias << push
     end
     Queue.prepend QueueClose
   end

lib/puma/reactor.rb

@@ -84,7 +84,7 @@ module Puma
         retry
       end
       # Wakeup all remaining objects on shutdown.
-      @timeouts.each(&@block.method(:call))
+      @timeouts.each(&@block)
       @selector.close
     end
 

test/test_puma_server.rb

@@ -972,6 +972,22 @@ EOF
       [204, {}, []]
     }
 
+    pool = @server.instance_variable_get(:@thread_pool)
+
+    # Trigger potential race condition by pausing Reactor#add until shutdown begins.
+    if options.fetch(:queue_requests, true)
+      reactor = @server.instance_variable_get(:@reactor)
+      reactor.instance_variable_set(:@pool, pool)
+      reactor.extend(Module.new do
+        def add(client)
+          if client.env['REQUEST_PATH'] == '/s2'
+            Thread.pass until @pool.instance_variable_get(:@shutdown)
+          end
+          super
+        end
+      end)
+    end
+
     s1 = nil
     s2 = send_http post ?
       "POST /s2 HTTP/1.1\r\nHost: test.com\r\nContent-Type: text/plain\r\nContent-Length: 5\r\n\r\nhi!" :
@@ -982,7 +998,7 @@ EOF
       app_finished.signal if s1_complete
     end
     @server.stop
-    Thread.pass until @server.instance_variable_get(:@thread_pool).instance_variable_get(:@shutdown)
+    Thread.pass until pool.instance_variable_get(:@shutdown)
 
     assert_match(s1_response, s1.gets) if s1_response