Use multiprocessing to run tasks in child processes

.travis.yml

@@ -1,9 +1,10 @@
 language: python
+sudo: false
 python:
 - '2.7'
 - '3.4'
 install:
-- pip install -r requirements.txt
+- pip install -r test-requirements.txt
 script: python manage.py test
 deploy:
   provider: pypi

README.md

@@ -127,3 +127,7 @@ To start a worker:
     manage.py worker [queue_name]
 
 `queue_name` is optional, and will default to `default`
+
+## Testing
+
+It may be necessary to supply a DATABASE_PORT environment variable.

django_dbq/management/commands/worker.py

@@ -6,6 +6,7 @@
 from simplesignals.process import WorkerProcessBase
 from time import sleep
 import logging
+import multiprocessing
 
 
 logger = logging.getLogger(__name__)
@@ -14,18 +15,8 @@
 DEFAULT_QUEUE_NAME = 'default'
 
 
-def process_job(queue_name):
-    """This function grabs the next available job for a given queue, and runs its next task."""
-
-    with transaction.atomic():
-        job = Job.objects.get_ready_or_none(queue_name)
-        if not job:
-            return
-
-        logger.info('Processing job: name="%s" queue="%s" id=%s state=%s next_task=%s', job.name, queue_name, job.pk, job.state, job.next_task)
-        job.state = Job.STATES.PROCESSING
-        job.save()
-
+def run_next_task(job):
+    """Updates a job by running its next task"""
     try:
         task_function = import_by_path(job.next_task)
         task_function(job)
@@ -55,6 +46,23 @@ def process_job(queue_name):
         raise
 
 
+def process_job(queue_name):
+    """This function grabs the next available job for a given queue, and runs its next task."""
+
+    with transaction.atomic():
+        job = Job.objects.get_ready_or_none(queue_name)
+        if not job:
+            return
+
+        logger.info('Processing job: name="%s" queue="%s" id=%s state=%s next_task=%s', job.name, queue_name, job.pk, job.state, job.next_task)
+        job.state = Job.STATES.PROCESSING
+        job.save()
+
+    child = multiprocessing.Process(target=run_next_task, args=(job,))
+    child.start()
+    child.join()
+
+
 class Worker(WorkerProcessBase):
 
     process_title = "jobworker"

django_dbq/models.py

@@ -66,7 +66,7 @@ class Job(models.Model):
     queue_name = models.CharField(max_length=20, default='default', db_index=True)
 
     class Meta:
-        ordering = ['-created']
+        ordering = ['created']
 
     objects = JobManager()
 
@@ -100,3 +100,4 @@ def run_creation_hook(self):
             logger.info("Running creation hook %s for new job", creation_hook_name)
             creation_hook_function = import_by_path(creation_hook_name)
             creation_hook_function(self)
+

django_dbq/tests.py

@@ -93,21 +93,29 @@ def test_create_job_with_queue(self):
     def test_get_next_ready_job(self):
         self.assertTrue(Job.objects.get_ready_or_none('default') is None)
 
-        Job.objects.create(name='testjob', state=Job.STATES.READY, created=datetime.now())
-        Job.objects.create(name='testjob', state=Job.STATES.PROCESSING, created=datetime.now())
-        expected = Job.objects.create(name='testjob', state=Job.STATES.READY, created=datetime.now() - timedelta(minutes=1))
+        Job.objects.create(name='testjob', state=Job.STATES.READY)
+        Job.objects.create(name='testjob', state=Job.STATES.PROCESSING)
+        expected = Job.objects.create(name='testjob', state=Job.STATES.READY)
+        expected.created = datetime.now() - timedelta(minutes=1)
+        expected.save()
 
         self.assertEqual(Job.objects.get_ready_or_none('default'), expected)
 
     def test_get_next_ready_job_created(self):
         """
-        Created jobs should be picked too
+        Created jobs should be picked too.
+
+        We create three jobs, and expect the oldest in NEW or READY to be
+        selected by get_ready_or_none (the model is ordered by 'created' and the
+        query picks the .first())
         """
         self.assertTrue(Job.objects.get_ready_or_none('default') is None)
 
-        Job.objects.create(name='testjob', state=Job.STATES.NEW, created=datetime.now())
-        Job.objects.create(name='testjob', state=Job.STATES.PROCESSING, created=datetime.now())
-        expected = Job.objects.create(name='testjob', state=Job.STATES.NEW, created=datetime.now() - timedelta(minutes=1))
+        Job.objects.create(name='testjob', state=Job.STATES.NEW)
+        Job.objects.create(name='testjob', state=Job.STATES.PROCESSING)
+        expected = Job.objects.create(name='testjob', state=Job.STATES.NEW)
+        expected.created = datetime.now() - timedelta(minutes=1)
+        expected.save()
 
         self.assertEqual(Job.objects.get_ready_or_none('default'), expected)
 

test-requirements.txt

@@ -0,0 +1,2 @@
+-r requirements.txt
+pymysql==0.6.7

testsettings.py

@@ -1,7 +1,12 @@
+import os
+import pymysql
+pymysql.install_as_MySQLdb()
+
 DATABASES = {
     'default': {
-        'ENGINE': 'django.db.backends.sqlite3',
-        'NAME': ':memory:',
+        'ENGINE': 'django.db.backends.mysql',
+        'NAME': 'django_db_queue',
+        'PORT': os.getenv('DATABASE_PORT', 3306),
     },
 }