Add better connection management.

To start using RQ, push a Redis connection up its stack, like so:

    from rq import push_connection
    push_connection(Redis())

rq/__init__.py

@@ -1,6 +1,7 @@
 import uuid
 from pickle import loads, dumps
-from rdb import conn
+from .conn import current_connection, push_connection, pop_connection
+from .queue import Queue
 
 def to_queue_key(queue_name):
     return 'rq:%s' % (queue_name,)
@@ -13,7 +14,7 @@ class DelayedResult(object):
     @property
     def return_value(self):
         if self._rv is None:
-            rv = conn.get(self.key)
+            rv = current_connection().get(self.key)
             if rv is not None:
                 # cache the result
                 self._rv = loads(rv)
@@ -31,10 +32,8 @@ class job(object):
             if f.__module__ == '__main__':
                 raise ValueError('Functions from the __main__ module cannot be processed by workers.')
             s = dumps((f, key, args, kwargs))
-            conn.rpush(queue_key, s)
+            current_connection().rpush(queue_key, s)
             return DelayedResult(key)
         f.delay = delay
         return f
 
-
-

rq/conn.py

@@ -0,0 +1,18 @@
+from werkzeug.local import LocalStack
+
+class NoRedisConnectionException(Exception):
+    pass
+
+_conn = LocalStack()
+
+def push_connection(redis_conn):
+    _conn.push(redis_conn)
+
+def pop_connection():
+    return _conn.pop()
+
+def current_connection():
+    conn = _conn.top
+    if conn is None:
+        raise NoRedisConnectionException('Connect to Redis first.')
+    return conn

rq/queue.py

@@ -1,3 +1,5 @@
+from . import current_connection
+
 def to_queue_key(queue_name):
     return 'rq:%s' % (queue_name,)
 
@@ -13,5 +15,9 @@ class Queue(object):
     def key(self):
         return self._key
 
+    @property
+    def empty(self):
+        return current_connection().llen(self.key) == 0
+
     def __str__(self):
         return self.name

rq/worker.py

@@ -5,8 +5,8 @@ import time
 import procname
 from logbook import Logger
 from pickle import loads, dumps
-from rdb import conn
 from .queue import Queue
+from .conn import current_connection
 
 class NoQueueError(Exception): pass
 
@@ -45,7 +45,7 @@ class Worker(object):
     def work(self):
         while True:
             self.procline('Waiting on %s' % (', '.join(self.queue_names()),))
-            queue, msg = conn.blpop(self.queue_keys())
+            queue, msg = current_connection().blpop(self.queue_keys())
             self.fork_and_perform_job(queue, msg)
 
     def fork_and_perform_job(self, queue, msg):
@@ -80,7 +80,7 @@ class Worker(object):
             else:
                 self.log.info('Job ended normally without result')
         if rv is not None:
-            p = conn.pipeline()
-            conn.set(key, dumps(rv))
-            conn.expire(key, self.rv_ttl)
+            p = current_connection().pipeline()
+            p.set(key, dumps(rv))
+            p.expire(key, self.rv_ttl)
             p.execute()