From eadc7db29f6ef6bbd016fbbc5882d1266b75e3dd Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Thu, 18 Apr 2013 22:11:43 +0700
Subject: [PATCH 1/7] First stab at writing implementing job dependency.

---
 rq/job.py            | 57 +++++++++++++++++++++++++++++++++++++++++---
 rq/queue.py          | 29 ++++++++++++++++++----
 rq/worker.py         |  1 +
 tests/test_job.py    | 35 ++++++++++++++++++++++++++-
 tests/test_queue.py  | 25 +++++++++++++++++++
 tests/test_worker.py |  9 +++++++
 6 files changed, 148 insertions(+), 8 deletions(-)

diff --git a/rq/job.py b/rq/job.py
index a4772a41..2a6efcfb 100644
--- a/rq/job.py
+++ b/rq/job.py
@@ -64,7 +64,7 @@ class Job(object):
     # Job construction
     @classmethod
     def create(cls, func, args=None, kwargs=None, connection=None,
-               result_ttl=None, status=None):
+               result_ttl=None, status=None, parent=None):
         """Creates a new Job instance for the given function, arguments, and
         keyword arguments.
         """
@@ -87,6 +87,9 @@ class Job(object):
         job.description = job.get_call_string()
         job.result_ttl = result_ttl
         job._status = status
+        # parent could be job instance or id
+        if parent is not None:
+            job._parent_id = parent.id if isinstance(parent, Job) else parent
         return job
 
     @property
@@ -119,6 +122,20 @@ class Job(object):
     def is_started(self):
         return self.status == Status.STARTED
 
+    @property
+    def parent(self):
+        """Returns a job's parent. To avoid repeated Redis fetches, we cache
+        job.parent as job._parent.
+        """
+        if self._parent_id is None:
+            return None
+        if hasattr(self, '_parent'):
+            return self._parent
+        job = Job.fetch(self._parent_id, connection=self.connection)
+        job.refresh()
+        self._parent = job
+        return job
+
     @property
     def func(self):
         func_name = self.func_name
@@ -185,6 +202,7 @@ class Job(object):
         self.timeout = None
         self.result_ttl = None
         self._status = None
+        self._parent_id = None
         self.meta = {}
 
 
@@ -208,11 +226,21 @@ class Job(object):
         """The Redis key that is used to store job hash under."""
         return 'rq:job:%s' % (job_id,)
 
+    @classmethod
+    def waitlist_key_for(cls, job_id):
+        """The Redis key that is used to store job hash under."""
+        return 'rq:job:%s:waitlist' % (job_id,)
+
     @property
     def key(self):
         """The Redis key that is used to store job hash under."""
         return self.key_for(self.id)
 
+    @property
+    def waitlist_key(self):
+        """The Redis key that is used to store job hash under."""
+        return self.waitlist_key_for(self.id)
+
     @property  # noqa
     def job_tuple(self):
         """Returns the job tuple that encodes the actual function call that
@@ -285,6 +313,7 @@ class Job(object):
         self.timeout = int(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._status = obj.get('status') if obj.get('status') else None
+        self._parent_id = obj.get('parent_id', None)
         self.meta = unpickle(obj.get('meta')) if obj.get('meta') else {}
 
     def save(self, pipeline=None):
@@ -315,6 +344,8 @@ class Job(object):
             obj['result_ttl'] = self.result_ttl
         if self._status is not None:
             obj['status'] = self._status
+        if self._parent_id is not None:
+            obj['parent_id'] = self._parent_id
         if self.meta:
             obj['meta'] = dumps(self.meta)
 
@@ -381,7 +412,26 @@ class Job(object):
         elif ttl > 0:
             connection = pipeline if pipeline is not None else self.connection
             connection.expire(self.key, ttl)
+
+    def register_dependency(self):
+        """Jobs may have a waitlist. Jobs in this waitlist are enqueued
+        only if the parent job is successfully performed. We maintain this
+        waitlist in Redis, with key that looks something like:
+            
+            rq:job:job_id:waitlist = ['job_id_1', 'job_id_2']
         
+        This method puts the job on it's parent's waitlist.
+        """
+        # TODO: This can probably be pipelined
+        self.connection.rpush(Job.waitlist_key_for(self._parent_id), self.id)
+
+    def get_waitlist(self):
+        """Returns all job ids in the waitlist.
+        """
+        # TODO: This can probably be pipelined
+
+        return self.connection.lrange(
+            self.waitlist_key, 0, self.connection.llen(self.waitlist_key) - 1)
 
     def __str__(self):
         return '<Job %s: %s>' % (self.id, self.description)
@@ -413,10 +463,11 @@ class Job(object):
 
     def __setattr__(self, name, value):
         # Ignore the "private" fields
-        private_attrs = set(['origin', '_func_name', 'ended_at',
+        private_attrs = set(('origin', '_func_name', 'ended_at',
             'description', '_args', 'created_at', 'enqueued_at', 'connection',
             '_result', 'result', 'timeout', '_kwargs', 'exc_info', '_id',
-            'data', '_instance', 'result_ttl', '_status', 'status', 'meta'])
+            'data', '_instance', 'result_ttl', '_status', 'status',
+            '_parent_id', '_parent', 'parent', 'meta'))
 
         if name in private_attrs:
             object.__setattr__(self, name, value)
diff --git a/rq/queue.py b/rq/queue.py
index 3bf5d009..f70033a9 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -113,7 +113,8 @@ class Queue(object):
         """Pushes a job ID on the corresponding Redis queue."""
         self.connection.rpush(self.key, job_id)
 
-    def enqueue_call(self, func, args=None, kwargs=None, timeout=None, result_ttl=None): #noqa
+    def enqueue_call(self, func, args=None, kwargs=None, timeout=None, 
+                     result_ttl=None, after=None):
         """Creates a job to represent the delayed function call and enqueues
         it.
 
@@ -123,7 +124,14 @@ class Queue(object):
         """
         timeout = timeout or self._default_timeout
         job = Job.create(func, args, kwargs, connection=self.connection,
-                         result_ttl=result_ttl, status=Status.QUEUED)
+                         result_ttl=result_ttl, status=Status.QUEUED,
+                         parent=after)
+        # If job depends on another job to finish, register itself on it's
+        # parent's waitlist instead of enqueueing it
+        if after is not None:
+            job.register_dependency()
+            job.save()
+            return job
         return self.enqueue_job(job, timeout=timeout)
 
     def enqueue(self, f, *args, **kwargs):
@@ -149,15 +157,18 @@ class Queue(object):
         #     q.enqueue(foo, args=(1, 2), kwargs={'a': 1}, timeout=30)
         timeout = None
         result_ttl = None
-        if 'args' in kwargs or 'kwargs' in kwargs:
+        after = None
+        if 'args' in kwargs or 'kwargs' in kwargs or 'after' in kwargs:
             assert args == (), 'Extra positional arguments cannot be used when using explicit args and kwargs.'  # noqa
             timeout = kwargs.pop('timeout', None)
             args = kwargs.pop('args', None)
             result_ttl = kwargs.pop('result_ttl', None)
+            after = kwargs.pop('after', None)
             kwargs = kwargs.pop('kwargs', None)
 
         return self.enqueue_call(func=f, args=args, kwargs=kwargs,
-                                 timeout=timeout, result_ttl=result_ttl)
+                                 timeout=timeout, result_ttl=result_ttl,
+                                 after=after)
 
     def enqueue_job(self, job, timeout=None, set_meta_data=True):
         """Enqueues a job for delayed execution.
@@ -188,6 +199,16 @@ class Queue(object):
             job.save()
         return job
 
+    def enqueue_waitlist(self, job):
+        """Enqueues all jobs in the waitlist and clears it"""
+        # TODO: can probably be pipelined
+        job_ids = job.get_waitlist()
+        for job_id in job.get_waitlist():
+            waitlisted_job = Job.fetch(job_id, connection=self.connection)
+            self.enqueue_job(waitlisted_job)
+        if job_ids:
+            self.connection.delete(job.waitlist_key)
+
     def pop_job_id(self):
         """Pops a given job ID from this Redis queue."""
         return self.connection.lpop(self.key)
diff --git a/rq/worker.py b/rq/worker.py
index 8f1da270..8d43f9f8 100644
--- a/rq/worker.py
+++ b/rq/worker.py
@@ -328,6 +328,7 @@ class Worker(object):
                 self.connection.expire(self.key, (job.timeout or 180) + 60)
                 self.fork_and_perform_job(job)
                 self.connection.expire(self.key, self.default_worker_ttl)
+                queue.enqueue_waitlist(job)
 
                 did_perform_work = True
         finally:
diff --git a/tests/test_job.py b/tests/test_job.py
index 8b1d137d..87f649e1 100644
--- a/tests/test_job.py
+++ b/tests/test_job.py
@@ -131,6 +131,22 @@ class TestJob(RQTestCase):
                 self.testconn.hkeys(job.key),
                 ['created_at', 'data', 'description'])
 
+    def test_persistence_of_parent_job(self):
+        """Storing jobs with parent job, either instance or key."""
+        parent_job = Job.create(func=some_calculation)
+        parent_job.save()
+        job = Job.create(func=some_calculation, parent=parent_job)
+        job.save()
+        stored_job = Job.fetch(job.id)
+        self.assertEqual(stored_job._parent_id, parent_job.id)
+        self.assertEqual(stored_job.parent, parent_job)
+
+        job = Job.create(func=some_calculation, parent=parent_job.id)
+        job.save()
+        stored_job = Job.fetch(job.id)
+        self.assertEqual(stored_job._parent_id, parent_job.id)
+        self.assertEqual(stored_job.parent, parent_job)
+
     def test_store_then_fetch(self):
         """Store, then fetch."""
         job = Job.create(func=some_calculation, args=(3, 4), kwargs=dict(z=2))
@@ -242,10 +258,27 @@ class TestJob(RQTestCase):
         job.cleanup(ttl=-1)
         self.assertEqual(self.testconn.ttl(job.key), -1)
 
-        # Jobs with positive TTLs are eventually deleted 
+        # Jobs with positive TTLs are eventually deleted
         job.cleanup(ttl=100)
         self.assertEqual(self.testconn.ttl(job.key), 100)
 
         # Jobs with 0 TTL are immediately deleted
         job.cleanup(ttl=0)
         self.assertRaises(NoSuchJobError, Job.fetch, job.id, self.testconn)
+
+    def test_register_dependency(self):
+        """Test that jobs updates the correct job waitlist"""
+        job = Job.create(func=say_hello)
+        job._parent_id = 'id'
+        job.save()
+        job.register_dependency()
+        self.assertEqual(self.testconn.lpop('rq:job:id:waitlist'), job.id)
+
+    def test_get_waitlist(self):
+        """Test that all waitlisted job ids are fetched"""
+        job = Job.create(func=say_hello)
+        self.assertEqual(job.get_waitlist(), [])
+        self.testconn.lpush(job.waitlist_key, 'id_1')
+        self.assertEqual(job.get_waitlist(), ['id_1'])
+        self.testconn.lpush(job.waitlist_key, 'id_2')
+        self.assertEqual(job.get_waitlist(), ['id_2', 'id_1'])
diff --git a/tests/test_queue.py b/tests/test_queue.py
index 061c984b..b5960046 100644
--- a/tests/test_queue.py
+++ b/tests/test_queue.py
@@ -237,6 +237,31 @@ class TestQueue(RQTestCase):
         job = q.enqueue(say_hello)
         self.assertEqual(job.status, Status.QUEUED)
 
+    def test_enqueue_waitlist(self):
+        """Enqueueing a waitlist pushes all jobs in waitlist to queue"""
+        q = Queue()
+        parent_job = Job.create(func=say_hello)
+        parent_job.save()
+        job_1 = Job.create(func=say_hello, parent=parent_job)
+        job_1.save()
+        job_1.register_dependency()
+        job_2 = Job.create(func=say_hello, parent=parent_job)
+        job_2.save()
+        job_2.register_dependency()
+
+        # After waitlist is enqueued, job_1 and job_2 should be in queue
+        self.assertEqual(q.job_ids, [])
+        q.enqueue_waitlist(parent_job)
+        self.assertEqual(q.job_ids, [job_1.id, job_2.id])
+        self.assertFalse(self.testconn.exists(parent_job.waitlist_key))
+
+    def test_enqueue_job_with_dependency(self):
+        """Job with dependency is not queued right away"""
+        parent_job = Job.create(func=say_hello)
+        q = Queue()
+        q.enqueue_call(say_hello, after=parent_job)
+        self.assertEqual(q.job_ids, [])
+
 
 class TestFailedQueue(RQTestCase):
     def test_requeue_job(self):
diff --git a/tests/test_worker.py b/tests/test_worker.py
index d9e2fe52..143fdbca 100644
--- a/tests/test_worker.py
+++ b/tests/test_worker.py
@@ -234,3 +234,12 @@ class TestWorker(RQTestCase):
         self.assertEqual(job.is_queued, False)
         self.assertEqual(job.is_finished, False)
         self.assertEqual(job.is_failed, True)
+
+    def test_job_dependency(self):
+        q = Queue()
+        w = Worker([q])
+        parent_job = q.enqueue(say_hello)
+        job = q.enqueue_call(say_hello, after=parent_job)
+        w.work(burst=True)
+        job = Job.fetch(job.id)
+        self.assertEqual(job.status, 'finished')        

From 6550f866463cf3d25da5a4ee6b5ec5dcf31f01d3 Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Thu, 18 Apr 2013 22:18:56 +0700
Subject: [PATCH 2/7] Don't enqueue waitlisted jobs on failed execution.

---
 rq/queue.py          | 3 ++-
 rq/worker.py         | 3 ++-
 tests/test_worker.py | 9 ++++++++-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/rq/queue.py b/rq/queue.py
index f70033a9..31d33c9f 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -113,7 +113,7 @@ class Queue(object):
         """Pushes a job ID on the corresponding Redis queue."""
         self.connection.rpush(self.key, job_id)
 
-    def enqueue_call(self, func, args=None, kwargs=None, timeout=None, 
+    def enqueue_call(self, func, args=None, kwargs=None, timeout=None,
                      result_ttl=None, after=None):
         """Creates a job to represent the delayed function call and enqueues
         it.
@@ -123,6 +123,7 @@ class Queue(object):
         contain options for RQ itself.
         """
         timeout = timeout or self._default_timeout
+        # TODO: job with dependency shouldn't have "queued" as status
         job = Job.create(func, args, kwargs, connection=self.connection,
                          result_ttl=result_ttl, status=Status.QUEUED,
                          parent=after)
diff --git a/rq/worker.py b/rq/worker.py
index 8d43f9f8..6d35656c 100644
--- a/rq/worker.py
+++ b/rq/worker.py
@@ -328,7 +328,8 @@ class Worker(object):
                 self.connection.expire(self.key, (job.timeout or 180) + 60)
                 self.fork_and_perform_job(job)
                 self.connection.expire(self.key, self.default_worker_ttl)
-                queue.enqueue_waitlist(job)
+                if job.status == 'finished':
+                    queue.enqueue_waitlist(job)
 
                 did_perform_work = True
         finally:
diff --git a/tests/test_worker.py b/tests/test_worker.py
index 143fdbca..86158010 100644
--- a/tests/test_worker.py
+++ b/tests/test_worker.py
@@ -236,10 +236,17 @@ class TestWorker(RQTestCase):
         self.assertEqual(job.is_failed, True)
 
     def test_job_dependency(self):
+        """Waitlisted jobs are enqueued only if their parents don't fail"""
         q = Queue()
         w = Worker([q])
         parent_job = q.enqueue(say_hello)
         job = q.enqueue_call(say_hello, after=parent_job)
         w.work(burst=True)
         job = Job.fetch(job.id)
-        self.assertEqual(job.status, 'finished')        
+        self.assertEqual(job.status, 'finished')
+
+        parent_job = q.enqueue(div_by_zero)
+        job = q.enqueue_call(say_hello, after=parent_job)
+        w.work(burst=True)
+        job = Job.fetch(job.id)
+        self.assertNotEqual(job.status, 'finished')

From 18ff57ef352f39a8c9077cd33c46b0ec0634e242 Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Sun, 28 Apr 2013 11:11:36 +0700
Subject: [PATCH 3/7] Avoid race conditions when enqueueing job with
 dependency.

---
 rq/exceptions.py     |  4 ++++
 rq/queue.py          | 25 +++++++++++++++++++------
 tests/test_queue.py  |  9 ++++++++-
 tests/test_worker.py |  2 +-
 4 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/rq/exceptions.py b/rq/exceptions.py
index 982a5801..7f8df37d 100644
--- a/rq/exceptions.py
+++ b/rq/exceptions.py
@@ -17,3 +17,7 @@ class UnpickleError(Exception):
 
 class DequeueTimeout(Exception):
     pass
+
+
+class EnqueueError(Exception):
+    pass
\ No newline at end of file
diff --git a/rq/queue.py b/rq/queue.py
index 31d33c9f..da0154a9 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -1,10 +1,12 @@
 import times
 from .connections import resolve_connection
 from .job import Job, Status
-from .exceptions import (NoSuchJobError, UnpickleError,
-                         InvalidJobOperationError, DequeueTimeout)
+from .exceptions import (DequeueTimeout, EnqueueError, InvalidJobOperationError, 
+                         NoSuchJobError, UnpickleError)
 from .compat import total_ordering
 
+from redis import WatchError
+
 
 def get_failed_queue(connection=None):
     """Returns a handle to the special failed queue."""
@@ -127,12 +129,23 @@ class Queue(object):
         job = Job.create(func, args, kwargs, connection=self.connection,
                          result_ttl=result_ttl, status=Status.QUEUED,
                          parent=after)
-        # If job depends on another job to finish, register itself on it's
+        
+        # If job depends on an unfinished job, register itself on it's
         # parent's waitlist instead of enqueueing it
         if after is not None:
-            job.register_dependency()
-            job.save()
-            return job
+            with self.connection.pipeline() as pipe:
+                try:
+                    pipe.watch(after.key)
+                    if after.status != Status.FINISHED:
+                        job.register_dependency()
+                        job.save()
+                        return job
+                except WatchError:
+                    raise EnqueueError(
+                        'Parent job (%s) modified during enqueue process. ' +
+                        'Bailing out to avoid race conditions' % after.id
+                    )
+            
         return self.enqueue_job(job, timeout=timeout)
 
     def enqueue(self, f, *args, **kwargs):
diff --git a/tests/test_queue.py b/tests/test_queue.py
index b5960046..9304e42d 100644
--- a/tests/test_queue.py
+++ b/tests/test_queue.py
@@ -256,12 +256,19 @@ class TestQueue(RQTestCase):
         self.assertFalse(self.testconn.exists(parent_job.waitlist_key))
 
     def test_enqueue_job_with_dependency(self):
-        """Job with dependency is not queued right away"""
+        """Test enqueueing job with dependency"""
+        # Job with unfinished dependency is not immediately enqueued
         parent_job = Job.create(func=say_hello)
         q = Queue()
         q.enqueue_call(say_hello, after=parent_job)
         self.assertEqual(q.job_ids, [])
 
+        # Jobs dependent on finished jobs are immediately enqueued
+        parent_job.status = 'finished'
+        parent_job.save()
+        job = q.enqueue_call(say_hello, after=parent_job)
+        self.assertEqual(q.job_ids, [job.id])
+
 
 class TestFailedQueue(RQTestCase):
     def test_requeue_job(self):
diff --git a/tests/test_worker.py b/tests/test_worker.py
index 86158010..7e4bd2e9 100644
--- a/tests/test_worker.py
+++ b/tests/test_worker.py
@@ -236,7 +236,7 @@ class TestWorker(RQTestCase):
         self.assertEqual(job.is_failed, True)
 
     def test_job_dependency(self):
-        """Waitlisted jobs are enqueued only if their parents don't fail"""
+        """Enqueue waitlisted jobs only if their parents don't fail"""
         q = Queue()
         w = Worker([q])
         parent_job = q.enqueue(say_hello)

From 0dfb0413831c2df1df451fa50ffafdc85e0cbd78 Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Sun, 28 Apr 2013 11:20:39 +0700
Subject: [PATCH 4/7] Simplify enqueue_waitlist by using lpop.

---
 rq/job.py         | 8 --------
 rq/queue.py       | 8 ++++----
 tests/test_job.py | 9 ---------
 3 files changed, 4 insertions(+), 21 deletions(-)

diff --git a/rq/job.py b/rq/job.py
index 2a6efcfb..fbaa4248 100644
--- a/rq/job.py
+++ b/rq/job.py
@@ -425,14 +425,6 @@ class Job(object):
         # TODO: This can probably be pipelined
         self.connection.rpush(Job.waitlist_key_for(self._parent_id), self.id)
 
-    def get_waitlist(self):
-        """Returns all job ids in the waitlist.
-        """
-        # TODO: This can probably be pipelined
-
-        return self.connection.lrange(
-            self.waitlist_key, 0, self.connection.llen(self.waitlist_key) - 1)
-
     def __str__(self):
         return '<Job %s: %s>' % (self.id, self.description)
 
diff --git a/rq/queue.py b/rq/queue.py
index da0154a9..e06904df 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -216,12 +216,12 @@ class Queue(object):
     def enqueue_waitlist(self, job):
         """Enqueues all jobs in the waitlist and clears it"""
         # TODO: can probably be pipelined
-        job_ids = job.get_waitlist()
-        for job_id in job.get_waitlist():
+        while True:
+            job_id = self.connection.lpop(job.waitlist_key)
+            if job_id is None:
+                break
             waitlisted_job = Job.fetch(job_id, connection=self.connection)
             self.enqueue_job(waitlisted_job)
-        if job_ids:
-            self.connection.delete(job.waitlist_key)
 
     def pop_job_id(self):
         """Pops a given job ID from this Redis queue."""
diff --git a/tests/test_job.py b/tests/test_job.py
index 87f649e1..cafc8ad0 100644
--- a/tests/test_job.py
+++ b/tests/test_job.py
@@ -273,12 +273,3 @@ class TestJob(RQTestCase):
         job.save()
         job.register_dependency()
         self.assertEqual(self.testconn.lpop('rq:job:id:waitlist'), job.id)
-
-    def test_get_waitlist(self):
-        """Test that all waitlisted job ids are fetched"""
-        job = Job.create(func=say_hello)
-        self.assertEqual(job.get_waitlist(), [])
-        self.testconn.lpush(job.waitlist_key, 'id_1')
-        self.assertEqual(job.get_waitlist(), ['id_1'])
-        self.testconn.lpush(job.waitlist_key, 'id_2')
-        self.assertEqual(job.get_waitlist(), ['id_2', 'id_1'])

From 2e826e2b1f822a1c084c8239014160809162b1d2 Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Sun, 28 Apr 2013 11:27:50 +0700
Subject: [PATCH 5/7] Internally renamed the term "parent" to "dependency".

---
 rq/job.py           | 40 ++++++++++++++++++++--------------------
 rq/queue.py         |  2 +-
 tests/test_job.py   | 14 +++++++-------
 tests/test_queue.py |  4 ++--
 4 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/rq/job.py b/rq/job.py
index fbaa4248..9f5d2729 100644
--- a/rq/job.py
+++ b/rq/job.py
@@ -64,7 +64,7 @@ class Job(object):
     # Job construction
     @classmethod
     def create(cls, func, args=None, kwargs=None, connection=None,
-               result_ttl=None, status=None, parent=None):
+               result_ttl=None, status=None, dependency=None):
         """Creates a new Job instance for the given function, arguments, and
         keyword arguments.
         """
@@ -87,9 +87,9 @@ class Job(object):
         job.description = job.get_call_string()
         job.result_ttl = result_ttl
         job._status = status
-        # parent could be job instance or id
-        if parent is not None:
-            job._parent_id = parent.id if isinstance(parent, Job) else parent
+        # dependency could be job instance or id
+        if dependency is not None:
+            job._dependency_id = dependency.id if isinstance(dependency, Job) else dependency
         return job
 
     @property
@@ -123,17 +123,17 @@ class Job(object):
         return self.status == Status.STARTED
 
     @property
-    def parent(self):
-        """Returns a job's parent. To avoid repeated Redis fetches, we cache
-        job.parent as job._parent.
+    def dependency(self):
+        """Returns a job's dependency. To avoid repeated Redis fetches, we cache
+        job.dependency as job._dependency.
         """
-        if self._parent_id is None:
+        if self._dependency_id is None:
             return None
-        if hasattr(self, '_parent'):
-            return self._parent
-        job = Job.fetch(self._parent_id, connection=self.connection)
+        if hasattr(self, '_dependency'):
+            return self._dependency
+        job = Job.fetch(self._dependency_id, connection=self.connection)
         job.refresh()
-        self._parent = job
+        self._dependency = job
         return job
 
     @property
@@ -202,7 +202,7 @@ class Job(object):
         self.timeout = None
         self.result_ttl = None
         self._status = None
-        self._parent_id = None
+        self._dependency_id = None
         self.meta = {}
 
 
@@ -313,7 +313,7 @@ class Job(object):
         self.timeout = int(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._status = obj.get('status') if obj.get('status') else None
-        self._parent_id = obj.get('parent_id', None)
+        self._dependency_id = obj.get('dependency_id', None)
         self.meta = unpickle(obj.get('meta')) if obj.get('meta') else {}
 
     def save(self, pipeline=None):
@@ -344,8 +344,8 @@ class Job(object):
             obj['result_ttl'] = self.result_ttl
         if self._status is not None:
             obj['status'] = self._status
-        if self._parent_id is not None:
-            obj['parent_id'] = self._parent_id
+        if self._dependency_id is not None:
+            obj['dependency_id'] = self._dependency_id
         if self.meta:
             obj['meta'] = dumps(self.meta)
 
@@ -415,15 +415,15 @@ class Job(object):
 
     def register_dependency(self):
         """Jobs may have a waitlist. Jobs in this waitlist are enqueued
-        only if the parent job is successfully performed. We maintain this
+        only if the dependency job is successfully performed. We maintain this
         waitlist in Redis, with key that looks something like:
             
             rq:job:job_id:waitlist = ['job_id_1', 'job_id_2']
         
-        This method puts the job on it's parent's waitlist.
+        This method puts the job on it's dependency's waitlist.
         """
         # TODO: This can probably be pipelined
-        self.connection.rpush(Job.waitlist_key_for(self._parent_id), self.id)
+        self.connection.rpush(Job.waitlist_key_for(self._dependency_id), self.id)
 
     def __str__(self):
         return '<Job %s: %s>' % (self.id, self.description)
@@ -459,7 +459,7 @@ class Job(object):
             'description', '_args', 'created_at', 'enqueued_at', 'connection',
             '_result', 'result', 'timeout', '_kwargs', 'exc_info', '_id',
             'data', '_instance', 'result_ttl', '_status', 'status',
-            '_parent_id', '_parent', 'parent', 'meta'))
+            '_dependency_id', '_dependency', 'dependency', 'meta'))
 
         if name in private_attrs:
             object.__setattr__(self, name, value)
diff --git a/rq/queue.py b/rq/queue.py
index e06904df..486af1a8 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -128,7 +128,7 @@ class Queue(object):
         # TODO: job with dependency shouldn't have "queued" as status
         job = Job.create(func, args, kwargs, connection=self.connection,
                          result_ttl=result_ttl, status=Status.QUEUED,
-                         parent=after)
+                         dependency=after)
         
         # If job depends on an unfinished job, register itself on it's
         # parent's waitlist instead of enqueueing it
diff --git a/tests/test_job.py b/tests/test_job.py
index cafc8ad0..83a6eae6 100644
--- a/tests/test_job.py
+++ b/tests/test_job.py
@@ -135,17 +135,17 @@ class TestJob(RQTestCase):
         """Storing jobs with parent job, either instance or key."""
         parent_job = Job.create(func=some_calculation)
         parent_job.save()
-        job = Job.create(func=some_calculation, parent=parent_job)
+        job = Job.create(func=some_calculation, dependency=parent_job)
         job.save()
         stored_job = Job.fetch(job.id)
-        self.assertEqual(stored_job._parent_id, parent_job.id)
-        self.assertEqual(stored_job.parent, parent_job)
+        self.assertEqual(stored_job._dependency_id, parent_job.id)
+        self.assertEqual(stored_job.dependency, parent_job)
 
-        job = Job.create(func=some_calculation, parent=parent_job.id)
+        job = Job.create(func=some_calculation, dependency=parent_job.id)
         job.save()
         stored_job = Job.fetch(job.id)
-        self.assertEqual(stored_job._parent_id, parent_job.id)
-        self.assertEqual(stored_job.parent, parent_job)
+        self.assertEqual(stored_job._dependency_id, parent_job.id)
+        self.assertEqual(stored_job.dependency, parent_job)
 
     def test_store_then_fetch(self):
         """Store, then fetch."""
@@ -269,7 +269,7 @@ class TestJob(RQTestCase):
     def test_register_dependency(self):
         """Test that jobs updates the correct job waitlist"""
         job = Job.create(func=say_hello)
-        job._parent_id = 'id'
+        job._dependency_id = 'id'
         job.save()
         job.register_dependency()
         self.assertEqual(self.testconn.lpop('rq:job:id:waitlist'), job.id)
diff --git a/tests/test_queue.py b/tests/test_queue.py
index 9304e42d..83a129e3 100644
--- a/tests/test_queue.py
+++ b/tests/test_queue.py
@@ -242,10 +242,10 @@ class TestQueue(RQTestCase):
         q = Queue()
         parent_job = Job.create(func=say_hello)
         parent_job.save()
-        job_1 = Job.create(func=say_hello, parent=parent_job)
+        job_1 = Job.create(func=say_hello, dependency=parent_job)
         job_1.save()
         job_1.register_dependency()
-        job_2 = Job.create(func=say_hello, parent=parent_job)
+        job_2 = Job.create(func=say_hello, dependency=parent_job)
         job_2.save()
         job_2.register_dependency()
 

From 6ee45597ca589708ed5d4f8f68b84e4eb1925dab Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Tue, 7 May 2013 18:26:08 +0700
Subject: [PATCH 6/7] Don't fail if job dependency is modified during enqueue
 process.

---
 rq/exceptions.py |  5 +----
 rq/queue.py      | 27 ++++++++++++++-------------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/rq/exceptions.py b/rq/exceptions.py
index 7f8df37d..25e4f0e1 100644
--- a/rq/exceptions.py
+++ b/rq/exceptions.py
@@ -15,9 +15,6 @@ class UnpickleError(Exception):
         super(UnpickleError, self).__init__(message, inner_exception)
         self.raw_data = raw_data
 
+
 class DequeueTimeout(Exception):
     pass
-
-
-class EnqueueError(Exception):
-    pass
\ No newline at end of file
diff --git a/rq/queue.py b/rq/queue.py
index 0e8bdb7c..8a601022 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -1,7 +1,7 @@
 import times
 from .connections import resolve_connection
 from .job import Job, Status
-from .exceptions import (DequeueTimeout, EnqueueError, InvalidJobOperationError, 
+from .exceptions import (DequeueTimeout, InvalidJobOperationError,
                          NoSuchJobError, UnpickleError)
 from .compat import total_ordering
 
@@ -145,20 +145,21 @@ class Queue(object):
                          dependency=after)
         
         # If job depends on an unfinished job, register itself on it's
-        # parent's waitlist instead of enqueueing it
+        # parent's waitlist instead of enqueueing it.
+        # If WatchError is raised in the process, that means something else is
+        # modifying the dependency. In this case we simply retry
         if after is not None:
             with self.connection.pipeline() as pipe:
-                try:
-                    pipe.watch(after.key)
-                    if after.status != Status.FINISHED:
-                        job.register_dependency()
-                        job.save()
-                        return job
-                except WatchError:
-                    raise EnqueueError(
-                        'Parent job (%s) modified during enqueue process. ' +
-                        'Bailing out to avoid race conditions' % after.id
-                    )
+                while True:
+                    try:
+                        pipe.watch(after.key)
+                        if after.status != Status.FINISHED:
+                            job.register_dependency()
+                            job.save()
+                            return job
+                        break
+                    except WatchError:
+                        continue
             
         return self.enqueue_job(job, timeout=timeout)
 

From fd44ad39d49e1ea978384d1480653781fa75175c Mon Sep 17 00:00:00 2001
From: Selwin Ong <selwin.ong@gmail.com>
Date: Tue, 3 Sep 2013 08:03:50 +0700
Subject: [PATCH 7/7] Python 3 fixes for job dependency stuff.

---
 rq/job.py         | 2 +-
 rq/queue.py       | 2 +-
 tests/test_job.py | 3 ++-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/rq/job.py b/rq/job.py
index 7eaf5325..a10c340b 100644
--- a/rq/job.py
+++ b/rq/job.py
@@ -318,7 +318,7 @@ class Job(object):
         self.timeout = int(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._status = as_text(obj.get('status') if obj.get('status') else None)
-        self._dependency_id = obj.get('dependency_id', None)
+        self._dependency_id = as_text(obj.get('dependency_id', None))
         self.meta = unpickle(obj.get('meta')) if obj.get('meta') else {}
 
     def dump(self):
diff --git a/rq/queue.py b/rq/queue.py
index 79442ac9..e9f3c7f9 100644
--- a/rq/queue.py
+++ b/rq/queue.py
@@ -240,7 +240,7 @@ class Queue(object):
         """Enqueues all jobs in the waitlist and clears it"""
         # TODO: can probably be pipelined
         while True:
-            job_id = self.connection.lpop(job.waitlist_key)
+            job_id = as_text(self.connection.lpop(job.waitlist_key))
             if job_id is None:
                 break
             waitlisted_job = Job.fetch(job_id, connection=self.connection)
diff --git a/tests/test_job.py b/tests/test_job.py
index 13ef3687..bc70d5e4 100644
--- a/tests/test_job.py
+++ b/tests/test_job.py
@@ -7,6 +7,7 @@ try:
     from cPickle import loads
 except ImportError:
     from pickle import loads
+from rq.compat import as_text
 from rq.job import Job, get_current_job
 from rq.exceptions import NoSuchJobError, UnpickleError
 from rq.queue import Queue
@@ -288,4 +289,4 @@ class TestJob(RQTestCase):
         job._dependency_id = 'id'
         job.save()
         job.register_dependency()
-        self.assertEqual(self.testconn.lpop('rq:job:id:waitlist'), job.id)
+        self.assertEqual(as_text(self.testconn.lpop('rq:job:id:waitlist')), job.id)