Exit gracefully when user hits Ctrl+C in a worker.

The currently running task will be waited for, so it can gracefully
be finished.  Further execution will be stopped.

If, during this waiting phase, Ctrl+C is hit again, the worker and the
horse will be terminated forcefully (this means work could be lost or
partially finished).

rq/worker.py

@@ -1,9 +1,11 @@
 import sys
 import os
+import errno
 import random
 import time
 import procname
 import socket
+import signal
 from pickle import dumps
 try:
     from logbook import Logger
@@ -63,6 +65,7 @@ class Worker(object):
         self.rv_ttl = rv_ttl
         self._state = 'starting'
         self._is_horse = False
+        self._stopped = False
         self.log = Logger('worker')
 
 
@@ -154,14 +157,46 @@ class Worker(object):
 
     state = property(get_state, set_state)
 
+    @property
+    def stopped(self):
+        return self._stopped
+
+    def install_sigint_handler(self):
+        def request_force_stop(signum, frame):
+            """Terminates the application."""
+            self.log.warning('Cold shut down.')
+            raise SystemExit()
+
+        def request_stop(signum, frame):
+            signal.signal(signal.SIGINT, request_force_stop)
+
+            if self.is_horse:
+                self.log.debug('Ignoring SIGINT.')
+                return
+
+            self.log.warning('Warm shut down. Press Ctrl+C again for a cold shutdown.')
+
+            #if self.state == 'idle':
+            #    raise SystemExit()
+            self._stopped = True
+            self.log.debug('Stopping after current horse is finished.')
+
+        signal.signal(signal.SIGINT, request_stop)
+
+
     def _work(self, quit_when_done=False):
         """This method starts the work loop.
         """
+        self.install_sigint_handler()
+
         did_work = False
         self.register_birth()
         self.state = 'starting'
         try:
             while True:
+                if self.stopped:
+                    self.log.info('Stopping on request.')
+                    break
                 self.state = 'idle'
                 qnames = self.queue_names()
                 self.procline('Listening on %s' % (','.join(qnames)))
@@ -171,10 +206,12 @@ class Worker(object):
                 if job is None:
                     break
                 self.state = 'busy'
+
                 self.fork_and_perform_job(job)
+
                 did_work = True
         finally:
-            if not self._is_horse:
+            if not self.is_horse:
                 self.register_death()
         return did_work
 
@@ -201,7 +238,7 @@ class Worker(object):
             self.log = Logger('horse')
             try:
                 self.perform_job(job)
-            except Exception, e:
+            except Exception as e:
                 self.log.exception(e)
                 sys.exit(1)
             sys.exit(0)