Add option to enqueue a job's dependents when canceling (#1549)

* Add option to enqueue a jobs dependents when canceling

* Address @selwin's review

docs/contrib/index.md

@@ -55,9 +55,12 @@ Any job ID that is encountered by a worker for which no job hash is found in
 Redis is simply ignored.  This makes it easy to cancel jobs by simply removing
 the job hash.  In Python:
 
+```python
     from rq import cancel_job
     cancel_job('2eafc1e6-48c2-464b-a0ff-88fd199d039c')
+```
 
 Note that it is irrelevant on which queue the job resides.  When a worker
 eventually pops the job ID from the queue and notes that the Job hash does not
 exist (anymore), it simply discards the job ID and continues with the next.
+

docs/docs/jobs.md

@@ -171,6 +171,17 @@ Canceling a job will remove:
 Note that `job.cancel()` does **not** delete the job itself from Redis. If you want to
 delete the job from Redis and reclaim memory, use `job.delete()`.
 
+Note: if you want to enqueue the dependents of the job you 
+are trying to cancel use the following:
+
+```python
+from rq import cancel_job
+cancel_job(
+  '2eafc1e6-48c2-464b-a0ff-88fd199d039c',
+  enqueue_dependents=True
+)
+```
+
 ## 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.

rq/job.py

@@ -16,6 +16,8 @@ from enum import Enum
 from functools import partial
 from uuid import uuid4
 
+from redis import WatchError
+
 from rq.compat import as_text, decode_redis_hash, string_types
 from .connections import resolve_connection
 from .exceptions import DeserializationError, NoSuchJobError
@@ -46,11 +48,11 @@ class JobStatus(str, Enum):
 UNEVALUATED = object()
 
 
-def cancel_job(job_id, connection=None, serializer=None):
+def cancel_job(job_id, connection=None, serializer=None, enqueue_dependents=False):
     """Cancels the job with the given job ID, preventing execution.  Discards
     any job info (i.e. it can't be requeued later).
     """
-    Job.fetch(job_id, connection=connection, serializer=serializer).cancel()
+    Job.fetch(job_id, connection=connection, serializer=serializer).cancel(enqueue_dependents=enqueue_dependents)
 
 
 def get_current_job(connection=None, job_class=None):
@@ -676,32 +678,56 @@ class Job:
         meta = self.serializer.dumps(self.meta)
         self.connection.hset(self.key, 'meta', meta)
 
-    def cancel(self, pipeline=None):
+    def cancel(self, pipeline=None, enqueue_dependents=False):
         """Cancels the given job, which will prevent the job from ever being
         ran (or inspected).
 
         This method merely exists as a high-level API call to cancel jobs
         without worrying about the internals required to implement job
         cancellation.
-        """
-        pipeline = pipeline or self.connection.pipeline()
-        if self.origin:
-            from .registry import CanceledJobRegistry
-            from .queue import Queue
 
-            q = Queue(name=self.origin, connection=self.connection, serializer=self.serializer)
-            q.remove(self, pipeline=pipeline)
-
-            self.set_status(JobStatus.CANCELED, pipeline=pipeline)
+        You can enqueue the jobs dependents optionally, 
+        Same pipelining behavior as Queue.enqueue_dependents on whether or not a pipeline is passed in.
+        """
 
-            registry = CanceledJobRegistry(
-                self.origin,
-                self.connection,
-                job_class=self.__class__,
-                serializer=self.serializer
-            )
-            registry.add(self, pipeline=pipeline)
-        pipeline.execute()
+        from .registry import CanceledJobRegistry
+        from .queue import Queue
+        pipe = pipeline or self.connection.pipeline()
+        while True:
+            try:
+                q = Queue(
+                    name=self.origin,
+                    connection=self.connection,
+                    job_class=self.__class__,
+                    serializer=self.serializer
+                )
+                if enqueue_dependents:
+                    # Only WATCH if no pipeline passed, otherwise caller is responsible
+                    if pipeline is None:
+                        pipe.watch(self.dependents_key)
+                    q.enqueue_dependents(self, pipeline=pipeline)
+                q.remove(self, pipeline=pipe)
+
+                self.set_status(JobStatus.CANCELED, pipeline=pipe)
+
+                registry = CanceledJobRegistry(
+                    self.origin,
+                    self.connection,
+                    job_class=self.__class__,
+                    serializer=self.serializer                    
+                )
+                registry.add(self, pipeline=pipe)
+                if pipeline is None:
+                    pipe.execute()
+                break
+            except WatchError:
+                if pipeline is None:
+                    continue
+                else:
+                    # if the pipeline comes from the caller, we re-raise the
+                    # exception as it it the responsibility of the caller to
+                    # handle it
+                    raise
 
     def requeue(self):
         """Requeues job."""

tests/test_job.py

@@ -812,6 +812,54 @@ class TestJob(RQTestCase):
         job.delete()
         self.assertNotIn(job, registry)
 
+    def test_create_and_cancel_job_enqueue_dependents(self):
+        """Ensure job.cancel() works properly with enqueue_dependents=True"""
+        queue = Queue(connection=self.testconn)
+        dependency = queue.enqueue(fixtures.say_hello)
+        dependent = queue.enqueue(fixtures.say_hello, depends_on=dependency)
+
+        self.assertEqual(1, len(queue.get_jobs()))
+        self.assertEqual(1, len(queue.deferred_job_registry))
+        cancel_job(dependency.id, enqueue_dependents=True)
+        self.assertEqual(1, len(queue.get_jobs()))
+        self.assertEqual(0, len(queue.deferred_job_registry))
+        registry = CanceledJobRegistry(connection=self.testconn, queue=queue)
+        self.assertIn(dependency, registry)
+        self.assertEqual(dependency.get_status(), JobStatus.CANCELED)
+        self.assertIn(dependent, queue.get_jobs())
+        self.assertEqual(dependent.get_status(), JobStatus.QUEUED)
+        # If job is deleted, it's also removed from CanceledJobRegistry
+        dependency.delete()
+        self.assertNotIn(dependency, registry)
+
+    def test_create_and_cancel_job_enqueue_dependents_with_pipeline(self):
+        """Ensure job.cancel() works properly with enqueue_dependents=True"""
+        queue = Queue(connection=self.testconn)
+        dependency = queue.enqueue(fixtures.say_hello)
+        dependent = queue.enqueue(fixtures.say_hello, depends_on=dependency)
+
+        self.assertEqual(1, len(queue.get_jobs()))
+        self.assertEqual(1, len(queue.deferred_job_registry))
+        self.testconn.set('some:key', b'some:value')
+
+        with self.testconn.pipeline() as pipe:
+            pipe.watch('some:key')
+            self.assertEqual(self.testconn.get('some:key'), b'some:value')
+            dependency.cancel(pipeline=pipe, enqueue_dependents=True)
+            pipe.set('some:key', b'some:other:value')
+            pipe.execute()
+        self.assertEqual(self.testconn.get('some:key'), b'some:other:value')
+        self.assertEqual(1, len(queue.get_jobs()))
+        self.assertEqual(0, len(queue.deferred_job_registry))
+        registry = CanceledJobRegistry(connection=self.testconn, queue=queue)
+        self.assertIn(dependency, registry)
+        self.assertEqual(dependency.get_status(), JobStatus.CANCELED)
+        self.assertIn(dependent, queue.get_jobs())
+        self.assertEqual(dependent.get_status(), JobStatus.QUEUED)
+        # If job is deleted, it's also removed from CanceledJobRegistry
+        dependency.delete()
+        self.assertNotIn(dependency, registry)
+
     def test_create_and_cancel_job_with_serializer(self):
         """test creating and using cancel_job (with serializer) deletes job properly"""
         queue = Queue(connection=self.testconn, serializer=JSONSerializer)