Fix SIGINT when running on multiprocessing

^C was making the script hang (few scenarios possible).
This patch makes sure that the queue operations won't block forever.

Potentially related to #167

flake8/reporter.py

@@ -36,22 +36,37 @@ class BaseQReport(pep8.BaseReport):
         # spawn processes
         for i in range(self.n_jobs):
             p = multiprocessing.Process(target=self.process_main)
+            p.daemon = True
             p.start()
 
     def stop(self):
+        try:
             # collect queues
             for i in range(self.n_jobs):
                 self.task_queue.put('DONE')
                 self.update_state(self.result_queue.get())
+        except KeyboardInterrupt:
+            print('... stopped')
+        finally:
+            # cleanup queues to unlock threads
+            while not self.result_queue.empty():
+                self.result_queue.get_nowait()
+            while not self.task_queue.empty():
+                self.task_queue.get_nowait()
+
             super(BaseQReport, self).stop()
 
     def process_main(self):
+        try:
             if not self._loaded:
                 # Windows needs to parse again the configuration
                 from flake8.main import get_style_guide, DEFAULT_CONFIG
                 get_style_guide(parse_argv=True, config_file=DEFAULT_CONFIG)
             for filename in iter(self.task_queue.get, 'DONE'):
                 self.input_file(filename)
+        except KeyboardInterrupt:
+            pass
+        finally:
             self.result_queue.put(self.get_state())
 
     def get_state(self):