(partially) Fix #91 using a simple Alarm (SIGNAL) when exec-timeout

Introducing a timer (in this case 5 seconds) to ensure that the
execution time of the tokenizer takes less than 5 seconds. This
is a simple and standard POSIX signal handler.

This approach fixes the specific issues we have currently
with some inputs where the tokenization takes too much time. This
fix should be improved and be more generic:

 - Introducing statistics of content which timeouts.
 - Keeping a list/queue to further process those files using a different
   tokenizer approach. Maybe a set of "dirty" processes to handle the edge cases
   and to not impact the overall processing and analysis.
 - Make the timer configurable per module (at least for this one).

bin/Tokenize.py

@@ -28,6 +28,15 @@ from packages import Paste
 from pubsublogger import publisher
 
 from Helper import Process
+import signal
+
+class TimeoutException(Exception):
+    pass
+
+def timeout_handler(signum, frame):
+    raise TimeoutException
+
+signal.signal(signal.SIGALRM, timeout_handler)
 
 if __name__ == "__main__":
     publisher.port = 6380
@@ -44,10 +53,17 @@ if __name__ == "__main__":
         print message
         if message is not None:
             paste = Paste.Paste(message)
+            signal.alarm(5)
+            try:
                 for word, score in paste._get_top_words().items():
                     if len(word) >= 4:
                         msg = '{} {} {}'.format(paste.p_path, word, score)
                         p.populate_set_out(msg)
+            except TimeoutException:
+                 print ("{0} processing timeout".format(paste.p_path))
+                 continue
+            else:
+                signal.alarm(0)
         else:
             publisher.debug("Tokeniser is idling 10s")
             time.sleep(10)