Bugfix: LPOP does not support multiple queue arguments.

Redis' BLPOP command takes multiple queue arguments, but LPOP can only
take a single queue.  Therefore, we need to loop over all queues
manually, in order, and raise an exception is no more work is available.

rq/worker.py

@@ -12,6 +12,7 @@ from .queue import Queue
 from .proxy import conn
 
 class NoQueueError(Exception): pass
+class NoMoreWorkError(Exception): pass
 
 class Worker(object):
     def __init__(self, queue_names, rv_ttl=500):
@@ -45,16 +46,36 @@ class Worker(object):
         self.log.debug(message)
         procname.setprocname('rq: %s' % (message,))
 
+    def multi_lpop(self, queues):
+        # Redis' BLPOP command takes multiple queue arguments, but LPOP can
+        # only take a single queue.  Therefore, we need to loop over all
+        # queues manually, in order, and raise an exception is no more work
+        # is available
+        for queue in queues:
+            value = conn.lpop(queue)
+            if value is not None:
+                return value
+        return None
+
+    def pop_next_job(self, blocking):
+        queues = self.queue_keys()
+        if blocking:
+            queue, msg = conn.blpop(queues)
+        else:
+            value = self.multi_lpop(queues)
+            if value is None:
+                raise NoMoreWorkError('No more work.')
+            queue, msg = queue, value
+        return (queue, msg)
+
     def work(self, quit_when_done=False):
         while True:
             self.procline('Waiting on %s' % (', '.join(self.queue_names()),))
-            if quit_when_done:
-                value = conn.lpop(self.queue_keys())
-                if value is None:
-                    break  # No more work, so quitting
-                queue, msg = value
-            else:
-                queue, msg = conn.blpop(self.queue_keys())
+            try:
+                wait_for_job = not quit_when_done
+                queue, msg = self.pop_next_job(wait_for_job)
+            except NoMoreWorkError:
+                break
             self.fork_and_perform_job(queue, msg)
 
     def fork_and_perform_job(self, queue, msg):