Pimp backgroundjobs

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

developer_manual/app/backgroundjobs.rst

@@ -4,36 +4,122 @@ Background jobs (Cron)
 
 .. sectionauthor:: Bernhard Posselt <dev@bernhard-posselt.com>
 
-Background/cron jobs are usually registered in the :file:`appinfo/app.php` by using the **addRegularTask** method, the class and the method to run:
+Often there is a need to run background jobs. For example there are Background
+jobs in Nextcloud that send out the activity emails. Or expire the trashbin.
 
-.. code-block:: php
+Types of background jobs
+------------------------
+Nextcloud by default offers you two types of background jobs. The ``\OCP\BackgroundJob\QueuedJob``
+and ```\OCP\BackgroundJob\TimedJob``.
 
-    <?php
-    \OCP\Backgroundjob::addRegularTask('\OCA\MyApp\Cron\SomeTask', 'run');
+The ``QueuedJob`` is for one time jobs. This can for example be triggered by inserting
+a job because an event happened. The ``TimedJob`` has a method ``setInterval`` where
+you can set the time minimum time in seconds between the jobs (from the constructor).
+This is useful in case you want to have a job that is run at most once a day for example.
 
-The class for the above example would live in :file:`cron/sometask.php`. Try to keep the method as small as possible because its hard to test static methods. Simply reuse the app container and execute a service that was registered in it:
+Of course you can customize this all to your liking by just extending ``\OCP\BackgroundJob\Job``
+
+Writing a background job
+------------------------
+
+Writing a background job is rather straight forward. You write a class and extend
+your job class of choice.
 
 .. code-block:: php
 
     <?php
     namespace OCA\MyApp\Cron;
 
-    use \OCA\MyApp\AppInfo\Application;
+    use \OCA\MyApp\Service\SomeService;
+    use \OCP\BackgroundJob\TimedJob;
 
-    class SomeTask {
+    class SomeTask extends TimedJob {
 
-        public static function run() {
-            $app = new Application();
-            $container = $app->getContainer();
-            $container->query('SomeService')->run();
+        private $myService;
+
+        public function __construct(ITimeFactory $time, SomeService $service) {
+            parent::__construct($time);
+            $this->myService = $service;
+
+            // Run once an hour
+            parent::setInterval(3600);
+        }
+
+        public static function run($arguments) {
+            $this->myService->doCron($arguments['uid']);
         }
 
     }
 
-Don't forget to configure the cron service on the server by executing::
+As you can see our dependency injection also works just fine for background jobs.
+The ITimeFactory always needs to be passed to the parent constructor. Since it is
+required to be set.
 
-    sudo crontab -u http -e
+In this case it is a background job that runs every hour. And we take the ``uid`` arguemnt
+to pass on to the service to run the background job.
 
-where **http** is your Web server user, and add::
+The ``run`` function is the main thing you need to implement and where all the
+logic happens.
 
-    */15  *  *  *  * php -f /srv/http/nextcloud/cron.php
+Registering a background job
+----------------------------
+
+Now that you have written your background job there is of course the small matter of
+how to make sure the system actually runs your job. In order to do this your
+job needs to be registered.
+
+info.xml
+^^^^^^^^
+
+You can register your jobs in your info.xml by addning;
+
+.. code-block:: xml
+
+    <background-jobs>
+		  <job>OCA\MyApp\Cron\SomeTask</job>
+    </background-jobs>
+
+This will on install/update of the application add the job ``OCA\MyApp\Cron\SomeTask``.
+Of course in this case the arguments passed to your ``run`` function is just an empty
+array.
+
+Registering manually
+^^^^^^^^^^^^^^^^^^^^
+
+In case you want more fine grained control about when a background job is inserted
+and you want to pass arguments to it you need to manually register your background jobs.
+
+You do this by using ``\OCP\BackgroundJob\IJobList``. There you can add a job or remove a job.
+
+For example you could add or remove a certain job based on some controller:
+
+.. code-block:: php
+
+    <?php
+    namespace OCA\MyApp\Controller;
+
+    use \OCA\MyApp\Cron\SomeTask;
+    use \OCP\AppFramework\Controller;
+    use \OCP\BackgroundJob\IJobList;
+
+    class SomeController extends Controller {
+
+        private $jobList
+
+        public function __construct(string $appName, IRequest $request, IJobList $jobList) {
+            parent::__construct($appName, $request);
+
+            $this->jobList = $jobList;
+        }
+
+        public function addJob(string $uid) {
+            $this->jobList->add(SomeTask::class, ['uid' => $uid]);
+        }
+
+        public function removeJob(string $uid) {
+            $this->jobList->remove(SomeTask::class, ['uid' => $uid]);
+        }
+    }
+
+This provides more fine grained control and you can pass arguments to your background
+jobs easily.