Implement Customizable Serializer Support (#1219)

* Implement Customizable Serializer Support

* Refractor serializer instance methods

* Update tests with other serializers

* Edit function description

* Edit function description

* Raise appropriate exception

* Update tests for better code coverage

* Remove un-used imports and un-necessary code

* Refractor resolve_serializer

* Remove un-necessary alias from imports

* Add documentation

* Refractor tests, improve documentation

13 files changed, 190 insertions, 87 deletions

diff --git a/.travis.yml b/.travis.yml
index 168e736..1c4fe39 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,13 +3,12 @@ services:
   - redis
 matrix:
   include:
-  - python: "2.7"
   - python: "3.4"
   - python: "3.5"
   - python: "3.6"
   - python: "3.7"
   - python: "3.8"
-  - python: "pypy"
+  - python: "pypy3"
 install:
   - pip install -e .
   - pip install pytest-cov sentry-sdk codecov
diff --git a/docs/docs/jobs.md b/docs/docs/jobs.md
index 16c9860..b91ab21 100644
--- a/docs/docs/jobs.md
+++ b/docs/docs/jobs.md
@@ -82,6 +82,20 @@ job = Job.create(count_words_at_url,
           })
 ```
 
+## Job / Queue Creation with Custom Serializer
+
+When creating a job or queue, you can pass in a custom serializer that will be used for serializing / de-serializing job arguments.
+Serializers used should have at least `loads` and `dumps` method.
+The default serializer used is `pickle`
+
+```python
+import json
+from rq import Job, Queue
+
+job = Job(connection=connection, serializer=json)
+queue = Queue(connection=connection, serializer=json)
+```
+
 ## Retrieving a Job from Redis
 
 All job information is stored in Redis. You can inspect a job and its attributes
diff --git a/docs/docs/workers.md b/docs/docs/workers.md
index dc4fb6e..25d0095 100644
--- a/docs/docs/workers.md
+++ b/docs/docs/workers.md
@@ -202,6 +202,30 @@ queue = Queue('queue_name', connection=redis)
 workers = Worker.all(queue=queue)
 ```
 
+## Worker with Custom Serializer
+
+When creating a worker, you can pass in a custom serializer that will be implicitly passed to the queue.
+Serializers used should have at least `loads` and `dumps` method.
+The default serializer used is `pickle`
+
+```python
+import json
+from rq import Worker
+
+job = Worker('foo', serializer=json)
+```
+
+or when creating from a queue
+
+```python
+import json
+from rq import Queue, Worker
+
+w = Worker(Queue('foo'), serializer=json)
+```
+
+Queues will now use custom serializer
+
 
 ### Worker Statistics
 
diff --git a/rq/exceptions.py b/rq/exceptions.py
index 684bfb0..ba97f7c 100644
--- a/rq/exceptions.py
+++ b/rq/exceptions.py
@@ -19,12 +19,6 @@ class InvalidJobOperation(Exception):
     pass
 
 
-class UnpickleError(Exception):
-    def __init__(self, message, raw_data, inner_exception=None):
-        super(UnpickleError, self).__init__(message, inner_exception)
-        self.raw_data = raw_data
-
-
 class DequeueTimeout(Exception):
     pass
 
diff --git a/rq/job.py b/rq/job.py
index 69c18e1..15e706b 100644
--- a/rq/job.py
+++ b/rq/job.py
@@ -5,27 +5,17 @@ from __future__ import (absolute_import, division, print_function,
 import inspect
 import warnings
 import zlib
-from functools import partial
 from uuid import uuid4
 
 from rq.compat import as_text, decode_redis_hash, string_types, text_type
 
 from .connections import resolve_connection
-from .exceptions import InvalidJobDependency, NoSuchJobError, UnpickleError
+from .exceptions import NoSuchJobError
 from .local import LocalStack
 from .utils import (enum, import_attribute, parse_timeout, str_to_date,
                     utcformat, utcnow)
+from .serializers import resolve_serializer
 
-try:
-    import cPickle as pickle
-except ImportError:  # noqa  # pragma: no cover
-    import pickle
-
-
-# Serialize pickle dumps using the highest pickle protocol (binary, default
-# uses ascii)
-dumps = partial(pickle.dumps, protocol=pickle.HIGHEST_PROTOCOL)
-loads = pickle.loads
 
 JobStatus = enum(
     'JobStatus',
@@ -42,21 +32,6 @@ JobStatus = enum(
 UNEVALUATED = object()
 
 
-def unpickle(pickled_string):
-    """Unpickles a string, but raises a unified UnpickleError in case anything
-    fails.
-
-    This is a helper method to not have to deal with the fact that `loads()`
-    potentially raises many types of exceptions (e.g. AttributeError,
-    IndexError, TypeError, KeyError, etc.)
-    """
-    try:
-        obj = loads(pickled_string)
-    except Exception as e:
-        raise UnpickleError('Could not unpickle', pickled_string, e)
-    return obj
-
-
 def cancel_job(job_id, connection=None):
     """Cancels the job with the given job ID, preventing execution.  Discards
     any job info (i.e. it can't be requeued later).
@@ -89,7 +64,7 @@ class Job(object):
     def create(cls, func, args=None, kwargs=None, connection=None,
                result_ttl=None, ttl=None, status=None, description=None,
                depends_on=None, timeout=None, id=None, origin=None, meta=None,
-               failure_ttl=None):
+               failure_ttl=None, serializer=None):
         """Creates a new Job instance for the given function, arguments, and
         keyword arguments.
         """
@@ -103,7 +78,7 @@ class Job(object):
         if not isinstance(kwargs, dict):
             raise TypeError('{0!r} is not a valid kwargs dict'.format(kwargs))
 
-        job = cls(connection=connection)
+        job = cls(connection=connection, serializer=serializer)
         if id is not None:
             job.set_id(id)
 
@@ -214,8 +189,8 @@ class Job(object):
 
         return import_attribute(self.func_name)
 
-    def _unpickle_data(self):
-        self._func_name, self._instance, self._args, self._kwargs = unpickle(self.data)
+    def _deserialize_data(self):
+        self._func_name, self._instance, self._args, self._kwargs = self.serializer.loads(self.data)
 
     @property
     def data(self):
@@ -233,7 +208,7 @@ class Job(object):
                 self._kwargs = {}
 
             job_tuple = self._func_name, self._instance, self._args, self._kwargs
-            self._data = dumps(job_tuple)
+            self._data = self.serializer.dumps(job_tuple)
         return self._data
 
     @data.setter
@@ -247,7 +222,7 @@ class Job(object):
     @property
     def func_name(self):
         if self._func_name is UNEVALUATED:
-            self._unpickle_data()
+            self._deserialize_data()
         return self._func_name
 
     @func_name.setter
@@ -258,7 +233,7 @@ class Job(object):
     @property
     def instance(self):
         if self._instance is UNEVALUATED:
-            self._unpickle_data()
+            self._deserialize_data()
         return self._instance
 
     @instance.setter
@@ -269,7 +244,7 @@ class Job(object):
     @property
     def args(self):
         if self._args is UNEVALUATED:
-            self._unpickle_data()
+            self._deserialize_data()
         return self._args
 
     @args.setter
@@ -280,7 +255,7 @@ class Job(object):
     @property
     def kwargs(self):
         if self._kwargs is UNEVALUATED:
-            self._unpickle_data()
+            self._deserialize_data()
         return self._kwargs
 
     @kwargs.setter
@@ -295,11 +270,11 @@ class Job(object):
         return conn.exists(cls.key_for(job_id))
 
     @classmethod
-    def fetch(cls, id, connection=None):
+    def fetch(cls, id, connection=None, serializer=None):
         """Fetches a persisted job from its corresponding Redis key and
         instantiates it.
         """
-        job = cls(id, connection=connection)
+        job = cls(id, connection=connection, serializer=serializer)
         job.refresh()
         return job
 
@@ -327,7 +302,7 @@ class Job(object):
 
         return jobs
 
-    def __init__(self, id=None, connection=None):
+    def __init__(self, id=None, connection=None, serializer=None):
         self.connection = resolve_connection(connection)
         self._id = id
         self.created_at = utcnow()
@@ -350,6 +325,7 @@ class Job(object):
         self._status = None
         self._dependency_ids = []
         self.meta = {}
+        self.serializer = resolve_serializer(serializer)
 
     def __repr__(self):  # noqa  # pragma: no cover
         return '{0}({1!r}, enqueued_at={2!r})'.format(self.__class__.__name__,
@@ -451,7 +427,7 @@ class Job(object):
             rv = self.connection.hget(self.key, 'result')
             if rv is not None:
                 # cache the result
-                self._result = loads(rv)
+                self._result = self.serializer.loads(rv)
         return self._result
 
     """Backwards-compatibility accessor property `return_value`."""
@@ -480,9 +456,9 @@ class Job(object):
         result = obj.get('result')
         if result:
             try:
-                self._result = unpickle(obj.get('result'))
-            except UnpickleError:
-                self._result = 'Unpickleable return value'
+                self._result = self.serializer.loads(obj.get('result'))
+            except Exception as e:
+                self._result = "Unserializable return value"
         self.timeout = parse_timeout(obj.get('timeout')) if obj.get('timeout') else None
         self.result_ttl = int(obj.get('result_ttl')) if obj.get('result_ttl') else None  # noqa
         self.failure_ttl = int(obj.get('failure_ttl')) if obj.get('failure_ttl') else None  # noqa
@@ -492,7 +468,7 @@ class Job(object):
         self._dependency_ids = [as_text(dependency_id)] if dependency_id else []
 
         self.ttl = int(obj.get('ttl')) if obj.get('ttl') else None
-        self.meta = unpickle(obj.get('meta')) if obj.get('meta') else {}
+        self.meta = self.serializer.loads(obj.get('meta')) if obj.get('meta') else {}
 
         raw_exc_info = obj.get('exc_info')
         if raw_exc_info:
@@ -536,9 +512,9 @@ class Job(object):
         obj['ended_at'] = utcformat(self.ended_at) if self.ended_at else ''
         if self._result is not None:
             try:
-                obj['result'] = dumps(self._result)
-            except:
-                obj['result'] = 'Unpickleable return value'
+                obj['result'] = self.serializer.dumps(self._result)
+            except Exception as e:
+                obj['result'] = "Unserializable return value"
         if self.exc_info is not None:
             obj['exc_info'] = zlib.compress(str(self.exc_info).encode('utf-8'))
         if self.timeout is not None:
@@ -552,7 +528,7 @@ class Job(object):
         if self._dependency_ids:
             obj['dependency_id'] = self._dependency_ids[0]
         if self.meta and include_meta:
-            obj['meta'] = dumps(self.meta)
+            obj['meta'] = self.serializer.dumps(self.meta)
         if self.ttl:
             obj['ttl'] = self.ttl
 
@@ -575,7 +551,7 @@ class Job(object):
 
     def save_meta(self):
         """Stores job meta from the job instance to the corresponding Redis key."""
-        meta = dumps(self.meta)
+        meta = self.serializer.dumps(self.meta)
         self.connection.hset(self.key, 'meta', meta)
 
     def cancel(self, pipeline=None):
diff --git a/rq/queue.py b/rq/queue.py
index cff48fb..4316653 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -12,9 +12,10 @@ from redis import WatchError
 from .compat import as_text, string_types, total_ordering, utc
 from .connections import resolve_connection
 from .defaults import DEFAULT_RESULT_TTL
-from .exceptions import DequeueTimeout, NoSuchJobError, UnpickleError
+from .exceptions import DequeueTimeout, NoSuchJobError
 from .job import Job, JobStatus
 from .utils import backend_class, import_attribute, parse_timeout, utcnow
+from .serializers import resolve_serializer
 
 
 def compact(lst):
@@ -29,7 +30,7 @@ class Queue(object):
     redis_queues_keys = 'rq:queues'
 
     @classmethod
-    def all(cls, connection=None, job_class=None):
+    def all(cls, connection=None, job_class=None, serializer=None):
         """Returns an iterable of all Queues.
         """
         connection = resolve_connection(connection)
@@ -37,13 +38,13 @@ class Queue(object):
         def to_queue(queue_key):
             return cls.from_queue_key(as_text(queue_key),
                                       connection=connection,
-                                      job_class=job_class)
+                                      job_class=job_class, serializer=serializer)
         return [to_queue(rq_key)
                 for rq_key in connection.smembers(cls.redis_queues_keys)
                 if rq_key]
 
     @classmethod
-    def from_queue_key(cls, queue_key, connection=None, job_class=None):
+    def from_queue_key(cls, queue_key, connection=None, job_class=None, serializer=None):
         """Returns a Queue instance, based on the naming conventions for naming
         the internal Redis keys.  Can be used to reverse-lookup Queues by their
         Redis keys.
@@ -52,10 +53,10 @@ class Queue(object):
         if not queue_key.startswith(prefix):
             raise ValueError('Not a valid RQ queue key: {0}'.format(queue_key))
         name = queue_key[len(prefix):]
-        return cls(name, connection=connection, job_class=job_class)
+        return cls(name, connection=connection, job_class=job_class, serializer=serializer)
 
     def __init__(self, name='default', default_timeout=None, connection=None,
-                 is_async=True, job_class=None, **kwargs):
+                 is_async=True, job_class=None, serializer=None, **kwargs):
         self.connection = resolve_connection(connection)
         prefix = self.redis_queue_namespace_prefix
         self.name = name
@@ -73,6 +74,8 @@ class Queue(object):
                 job_class = import_attribute(job_class)
             self.job_class = job_class
 
+        self.serializer = resolve_serializer(serializer)
+
     def __len__(self):
         return self.count
 
@@ -269,7 +272,7 @@ class Queue(object):
             result_ttl=result_ttl, ttl=ttl, failure_ttl=failure_ttl,
             status=status, description=description,
             depends_on=depends_on, timeout=timeout, id=job_id,
-            origin=self.name, meta=meta
+            origin=self.name, meta=meta, serializer=self.serializer
         )
 
         return job
@@ -552,7 +555,7 @@ class Queue(object):
                 # Silently pass on jobs that don't exist (anymore),
                 # and continue in the look
                 continue
-            except UnpickleError as e:
+            except Exception as e:
                 # Attach queue information on the exception for improved error
                 # reporting
                 e.job_id = job_id
diff --git a/rq/serializers.py b/rq/serializers.py
new file mode 100644
index 0000000..c4b0e54
--- /dev/null
+++ b/rq/serializers.py
@@ -0,0 +1,25 @@
+import pickle
+
+from .compat import string_types
+from .utils import import_attribute
+
+
+def resolve_serializer(serializer):
+    """This function checks the user defined serializer for ('dumps', 'loads') methods
+    It returns a default pickle serializer if not found else it returns a MySerializer
+    The returned serializer objects implement ('dumps', 'loads') methods
+    Also accepts a string path to serializer that will be loaded as the serializer
+    """
+    if not serializer:
+        return pickle
+
+    if isinstance(serializer, string_types):
+        serializer = import_attribute(serializer)
+
+    default_serializer_methods = ('dumps', 'loads')
+
+    for instance_method in default_serializer_methods:
+        if not hasattr(serializer, instance_method):
+            raise NotImplementedError('Serializer should have (dumps, loads) methods.')
+
+    return serializer
diff --git a/rq/worker.py b/rq/worker.py
index 874640d..50d1733 100644
--- a/rq/worker.py
+++ b/rq/worker.py
@@ -41,6 +41,7 @@ from .utils import (backend_class, ensure_list, enum,
                     make_colorizer, utcformat, utcnow, utcparse)
 from .version import VERSION
 from .worker_registration import clean_worker_registry, get_keys
+from .serializers import resolve_serializer
 
 try:
     from setproctitle import setproctitle as setprocname
@@ -104,7 +105,7 @@ class Worker(object):
     log_job_description = True
 
     @classmethod
-    def all(cls, connection=None, job_class=None, queue_class=None, queue=None):
+    def all(cls, connection=None, job_class=None, queue_class=None, queue=None, serializer=None):
         """Returns an iterable of all Workers.
         """
         if queue:
@@ -116,7 +117,7 @@ class Worker(object):
         workers = [cls.find_by_key(as_text(key),
                                    connection=connection,
                                    job_class=job_class,
-                                   queue_class=queue_class)
+                                   queue_class=queue_class, serializer=serializer)
                    for key in worker_keys]
         return compact(workers)
 
@@ -132,7 +133,7 @@ class Worker(object):
 
     @classmethod
     def find_by_key(cls, worker_key, connection=None, job_class=None,
-                    queue_class=None):
+                    queue_class=None, serializer=None):
         """Returns a Worker instance, based on the naming conventions for
         naming the internal Redis keys.  Can be used to reverse-lookup Workers
         by their Redis keys.
@@ -149,7 +150,7 @@ class Worker(object):
 
         name = worker_key[len(prefix):]
         worker = cls([], name, connection=connection, job_class=job_class,
-                     queue_class=queue_class, prepare_for_work=False)
+                     queue_class=queue_class, prepare_for_work=False, serializer=serializer)
 
         worker.refresh()
 
@@ -161,7 +162,7 @@ class Worker(object):
                  queue_class=None, log_job_description=True,
                  job_monitoring_interval=DEFAULT_JOB_MONITORING_INTERVAL,
                  disable_default_exception_handler=False,
-                 prepare_for_work=True):  # noqa
+                 prepare_for_work=True, serializer=None):  # noqa
         if connection is None:
             connection = get_current_connection()
         self.connection = connection
@@ -177,10 +178,11 @@ class Worker(object):
         self.queue_class = backend_class(self, 'queue_class', override=queue_class)
         self.version = VERSION
         self.python_version = sys.version
+        self.serializer = resolve_serializer(serializer)
 
         queues = [self.queue_class(name=q,
                                    connection=connection,
-                                   job_class=self.job_class)
+                                   job_class=self.job_class, serializer=self.serializer)
                   if isinstance(q, string_types) else q
                   for q in ensure_list(queues)]
 
@@ -644,7 +646,7 @@ class Worker(object):
         if queues:
             self.queues = [self.queue_class(queue,
                                             connection=self.connection,
-                                            job_class=self.job_class)
+                                            job_class=self.job_class, serializer=self.serializer)
                            for queue in queues.split(',')]
 
     def increment_failed_job_count(self, pipeline=None):
diff --git a/tests/fixtures.py b/tests/fixtures.py
index 46cdaac..a1f507a 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -175,3 +175,10 @@ def kill_worker(pid, double_kill, interval=0.5):
         # give the worker time to switch signal handler
         time.sleep(interval)
         os.kill(pid, signal.SIGTERM)
+
+
+class Serializer(object):
+    def loads(self): pass
+
+    def dumps(self): pass
+
diff --git a/tests/test_job.py b/tests/test_job.py
index a7a1b27..25c37e2 100644
--- a/tests/test_job.py
+++ b/tests/test_job.py
@@ -2,15 +2,16 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
-import sys
+import json
 import time
+import queue
 import zlib
 from datetime import datetime
 
 from redis import WatchError
 
 from rq.compat import PY2, as_text
-from rq.exceptions import NoSuchJobError, UnpickleError
+from rq.exceptions import NoSuchJobError
 from rq.job import Job, JobStatus, cancel_job, get_current_job
 from rq.queue import Queue
 from rq.registry import (DeferredJobRegistry, FailedJobRegistry,
@@ -20,16 +21,7 @@ from rq.utils import utcformat
 from rq.worker import Worker
 from tests import RQTestCase, fixtures
 
-is_py2 = sys.version[0] == '2'
-if is_py2:
-    import Queue as queue
-else:
-    import queue as queue
-
-try:
-    from cPickle import loads, dumps
-except ImportError:
-    from pickle import loads, dumps
+from pickle import loads, dumps
 
 
 class TestJob(RQTestCase):
@@ -117,6 +109,17 @@ class TestJob(RQTestCase):
         self.assertEqual(job.instance, n)
         self.assertEqual(job.args, (4,))
 
+    def test_create_job_with_serializer(self):
+        """Creation of jobs with serializer for instance methods."""
+        # Test using json serializer
+        n = fixtures.Number(2)
+        job = Job.create(func=n.div, args=(4,), serializer=json)
+
+        self.assertIsNotNone(job.serializer)
+        self.assertEqual(job.func, n.div)
+        self.assertEqual(job.instance, n)
+        self.assertEqual(job.args, (4,))
+
     def test_create_job_from_string_function(self):
         """Creation of jobs using string specifier."""
         job = Job.create(func='tests.fixtures.say_hello', args=('World',))
@@ -273,7 +276,7 @@ class TestJob(RQTestCase):
         job.refresh()
 
         for attr in ('func_name', 'instance', 'args', 'kwargs'):
-            with self.assertRaises(UnpickleError):
+            with self.assertRaises(Exception):
                 getattr(job, attr)
 
     def test_job_is_unimportable(self):
@@ -371,13 +374,14 @@ class TestJob(RQTestCase):
         job = Job.create(func=fixtures.say_hello, args=('Lionel',))
         job._result = queue.Queue()
         job.save()
+
         self.assertEqual(
             self.testconn.hget(job.key, 'result').decode('utf-8'),
-            'Unpickleable return value'
+            'Unserializable return value'
         )
 
         job = Job.fetch(job.id)
-        self.assertEqual(job.result, 'Unpickleable return value')
+        self.assertEqual(job.result, 'Unserializable return value')
 
     def test_result_ttl_is_persisted(self):
         """Ensure that job's result_ttl is set properly"""
diff --git a/tests/test_queue.py b/tests/test_queue.py
index ffe08c5..7004aad 100644
--- a/tests/test_queue.py
+++ b/tests/test_queue.py
@@ -2,6 +2,7 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
+import json
 from datetime import datetime, timedelta
 
 from rq import Queue
@@ -29,6 +30,14 @@ class TestQueue(RQTestCase):
         self.assertEqual(q.name, 'my-queue')
         self.assertEqual(str(q), '<Queue my-queue>')
 
+    def test_create_queue_with_serializer(self):
+        """Creating queues with serializer."""
+        # Test using json serializer
+        q = Queue('queue-with-serializer', serializer=json)
+        self.assertEqual(q.name, 'queue-with-serializer')
+        self.assertEqual(str(q), '<Queue queue-with-serializer>')
+        self.assertIsNotNone(q.serializer)
+
     def test_create_default_queue(self):
         """Instantiating the default queue."""
         q = Queue()
diff --git a/tests/test_serializers.py b/tests/test_serializers.py
new file mode 100644
index 0000000..58d093f
--- /dev/null
+++ b/tests/test_serializers.py
@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+
+import json
+import pickle
+import queue
+import unittest
+
+from rq.serializers import resolve_serializer
+
+
+class TestSerializers(unittest.TestCase):
+    def test_resolve_serializer(self):
+        """Ensure function resolve_serializer works correctly"""
+        serializer = resolve_serializer(None)
+        self.assertIsNotNone(serializer)
+        self.assertEqual(serializer, pickle)
+
+        # Test using json serializer
+        serializer = resolve_serializer(json)
+        self.assertIsNotNone(serializer)
+
+        self.assertTrue(hasattr(serializer, 'dumps'))
+        self.assertTrue(hasattr(serializer, 'loads'))
+
+        # Test raise NotImplmentedError
+        with self.assertRaises(NotImplementedError):
+            resolve_serializer(object)
+
+        # Test raise Exception
+        with self.assertRaises(Exception):
+            resolve_serializer(queue.Queue())
+
+        # Test using path.to.serializer string
+        serializer = resolve_serializer('tests.fixtures.Serializer')
+        self.assertIsNotNone(serializer)
diff --git a/tests/test_worker.py b/tests/test_worker.py
index 5788d25..088213d 100644
--- a/tests/test_worker.py
+++ b/tests/test_worker.py
@@ -2,6 +2,7 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
+import json
 import os
 import shutil
 import signal
@@ -97,6 +98,14 @@ class TestWorker(RQTestCase):
         self.assertEqual(w.queues[0].name, 'foo')
         self.assertEqual(w.queues[1].name, 'bar')
 
+        # With string and serializer
+        w = Worker('foo', serializer=json)
+        self.assertEqual(w.queues[0].name, 'foo')
+
+        # With queue having serializer
+        w = Worker(Queue('foo'), serializer=json)
+        self.assertEqual(w.queues[0].name, 'foo')
+
     def test_work_and_quit(self):
         """Worker processes work, then quits."""
         fooq, barq = Queue('foo'), Queue('bar')