[Owncloud] Background Jobs

Wed Aug 22 14:53:40 UTC 2012

Hi,

Am 21.08.2012 18:02, schrieb Arthur Schiwon:
> On 08/15/2012 01:56 AM, Alessandro Cosentino wrote:
>> @Jakob: maybe I am missing something here, but is there a way for 
>> the
>> app developer to specify how often the job is executed?
>
> I'd guess it is up to the (web)cron settings. As far as i can see
> there are no parameters to pass, so (for now) you should take care
> about it in your method.

apparently I forgot to answer the first mail. It is not possible to 
pass a frequency to the job. This has several reasons: you don't know 
when the (web-) cronjob will be executed and you don't know when the 
next job will be executed when using the ajax.
Short: if your app needs a cooldown time you have to implement it 
yourself ...

> @Jakob: is it advisable to check if background jobs are enabled or
> did you implement a fallback (e.g. checking after every call if there
> is something to do?). Then it might make sense to provide an API 
> call.

If you rely on background jobs you should check if background jobs are 
enabled (OCP\Config::getAppValue('core','backgroundjobs_mode', 'none') 
!= 'none').
Take care,

Jakob

> Cheers
> Arthur
>
>>
>> Thanks,
>> Alessandro
>>
>>
>> On Mon, Aug 13, 2012 at 9:50 AM, Klaas Freitag 
>> <freitag at owncloud.com> wrote:
>>> On 13.08.2012 16:23, Jakob Sack wrote:
>>>>
>>>> Hi Klaas,
>>>>
>>>> maybe I chose the wrong words: To disable background jobs you do 
>>>> not
>>>> have to edit the program code but you must set the appconfig value
>>>> core:backgroundjobs_mode to "none".
>>>
>>> Ah, ok, sorry...
>>>
>>> IMO the important point is that an update does not kick out such 
>>> things, but
>>> you probably have taken care :)
>>>
>>> Thanks,
>>>
>>> Klaas
>>>
>>>
>>>>
>>>> Am 13.08.2012 11:49, schrieb Klaas Freitag:
>>>>>
>>>>> On 12.08.2012 11:29, Jakob Sack wrote:
>>>>>>
>>>>>> I removed the option from the UI. In the program code the option 
>>>>>> "none"
>>>>>> is still usable.
>>>>>
>>>>> Come on, isn't that the worst of all possible solutions? ;-)
>>>>>
>>>>> Changing the program code is not the best way to do app 
>>>>> configuration
>>>>> as the change will be gone with the next update. Why not put an 
>>>>> value
>>>>> in config.php if we do not want a GUI option?
>>>>>
>>>>> I think there should be an option to set up ownCloud completely 
>>>>> stand
>>>>> alone, without having the system seeking out for other web 
>>>>> services.
>>>>>
>>>>> Or do I get something wrong?
>>>>>
>>>>> Thx,
>>>>> Klaas
>>>>>
>>>>>>
>>>>>> Am 11.08.2012 23:08, schrieb Jan-Christoph Borchardt:
>>>>>>>
>>>>>>> Ah sorry, I phrased it wrong. I didn’t mean »just use AJAX all 
>>>>>>> the
>>>>>>> time and remove the option for cron jobs«, I meant »AJAX is 
>>>>>>> always
>>>>>>> available and has no negative effect, so let’s just not have an 
>>>>>>> option
>>>>>>> to deactivate background jobs«.
>>>>>>> Of course if the server supports it, cron should be used.
>>>>>>>
>>>>>>>
>>>>>>> TL;DR: Nice, let’s remove the option to deactivate background 
>>>>>>> jobs.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Sat, Aug 11, 2012 at 2:03 PM, Jakob Sack <mail at jakobsack.de> 
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hi Jan,
>>>>>>>>
>>>>>>>> thank you for the praise.
>>>>>>>> as far as I know there is no reason for completely disabling
>>>>>>>> background
>>>>>>>> jobs.
>>>>>>>> I strongly disaggree with you regarding your second argument. 
>>>>>>>> Using
>>>>>>>> AJAX
>>>>>>>> always is a bad idea. Exactly spoken, there are at least two 
>>>>>>>> problems
>>>>>>>> with
>>>>>>>> the ajax solution: if you installed ownCloud on a shared web 
>>>>>>>> hosting
>>>>>>>> service
>>>>>>>> and use it alone or with your family chances are high that 
>>>>>>>> there are
>>>>>>>> periods
>>>>>>>> with no one being online. Then you could miss news that are 
>>>>>>>> meant
>>>>>>>> to be
>>>>>>>> fetched every now and then. In this case a webcron serice 
>>>>>>>> would be
>>>>>>>> perfect.
>>>>>>>> On the other hand a large setup with several hundred users - 
>>>>>>>> we both
>>>>>>>> know
>>>>>>>> that they exist - should not be bombed with another hundred 
>>>>>>>> requests
>>>>>>>> every
>>>>>>>> minute. In this case it's better to use the systems cron 
>>>>>>>> service
>>>>>>>> which does
>>>>>>>> not have the limitations apaches processes might have.
>>>>>>>> regards,
>>>>>>>>
>>>>>>>> Jakob
>>>>>>>>
>>>>>>>> Am 11.08.2012 20:30, schrieb Jan-Christoph Borchardt:
>>>>>>>>
>>>>>>>>> Awesoooome! Does that mean that step-by-step, all the 
>>>>>>>>> »refresh« and
>>>>>>>>> »rescan« buttons can go away?
>>>>>>>>>
>>>>>>>>> Just one thing: You say »there are four options: using the 
>>>>>>>>> systems
>>>>>>>>> cron feature, using a webcron service, using AJAX or not 
>>>>>>>>> using
>>>>>>>>> background jobs at all.«
>>>>>>>>> Why even have the possibility to deactivate it? It’s a great 
>>>>>>>>> function
>>>>>>>>> which improves the experience silently, as with doing away 
>>>>>>>>> with the
>>>>>>>>> need for refresh buttons. And since doing it via AJAX is a 
>>>>>>>>> good
>>>>>>>>> default there’s no reason to not just do it like that always 
>>>>>>>>> – or is
>>>>>>>>> there?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Sat, Aug 11, 2012 at 7:07 AM, Jakob Sack 
>>>>>>>>> <mail at jakobsack.de>
>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> yesterday I pushed the new Background Jobs system to 
>>>>>>>>>> ownCloud
>>>>>>>>>> master. As
>>>>>>>>>> you
>>>>>>>>>> can guess from the name, this feature allows ownCloud to do 
>>>>>>>>>> certain
>>>>>>>>>> tasks
>>>>>>>>>> in
>>>>>>>>>> the background without blocking the UI. It also makes it 
>>>>>>>>>> possible to
>>>>>>>>>> execute
>>>>>>>>>> some tasks without any need of user interaction, for example
>>>>>>>>>> fetching
>>>>>>>>>> news
>>>>>>>>>> while the user is on holidays.
>>>>>>>>>>  From a users perspective there is not much to pay attention 
>>>>>>>>>> to,
>>>>>>>>>> background
>>>>>>>>>> jobs tries to get out of the way as much as possible. On the 
>>>>>>>>>> other
>>>>>>>>>> hand,
>>>>>>>>>> administrators can use the settings interface to set the way
>>>>>>>>>> background
>>>>>>>>>> jobs
>>>>>>>>>> are executed. There are four options: using the systems cron
>>>>>>>>>> feature,
>>>>>>>>>> using
>>>>>>>>>> a webcron service, using AJAX or not using background jobs 
>>>>>>>>>> at all.
>>>>>>>>>> Using
>>>>>>>>>> the
>>>>>>>>>> systems cron feature is the preferred way. It allows regular
>>>>>>>>>> executed
>>>>>>>>>> jobs
>>>>>>>>>> without the limitations the web server may have. The second
>>>>>>>>>> recommended
>>>>>>>>>> option is the webcron implementation. By registering your 
>>>>>>>>>> ownCloud
>>>>>>>>>> cron.php
>>>>>>>>>> address at a webcron service like [1] you ensure that 
>>>>>>>>>> background
>>>>>>>>>> jobs
>>>>>>>>>> will
>>>>>>>>>> be executed regularly. Using AJAX is the default option, 
>>>>>>>>>> although
>>>>>>>>>> the
>>>>>>>>>> least
>>>>>>>>>> reliable. Every time a  user visits the page a single 
>>>>>>>>>> background
>>>>>>>>>> job gets
>>>>>>>>>> executed. The disadvantage of this solution compared to the 
>>>>>>>>>> webcron
>>>>>>>>>> service
>>>>>>>>>> is that it requires regular visits of the page. The reason 
>>>>>>>>>> for
>>>>>>>>>> making
>>>>>>>>>> this
>>>>>>>>>> option the default is that this solution simply does not 
>>>>>>>>>> require
>>>>>>>>>> access
>>>>>>>>>> to
>>>>>>>>>> the system or registration on some third party service.
>>>>>>>>>> When you are implementing background jobs in your app, 
>>>>>>>>>> please be
>>>>>>>>>> aware of
>>>>>>>>>> the difference between the AJAX/Webcron and the cron
>>>>>>>>>> implementation! The
>>>>>>>>>> AJAX/Webcron implementation gets started by
>>>>>>>>>> your-favorite-web-server, so
>>>>>>>>>> you
>>>>>>>>>> might have some limitations on execution time or memory. 
>>>>>>>>>> These
>>>>>>>>>> limitations
>>>>>>>>>> do not affect the system cron implementation, which calls 
>>>>>>>>>> php
>>>>>>>>>> from the
>>>>>>>>>> command line. As a consequence, you should split large tasks 
>>>>>>>>>> when
>>>>>>>>>> not
>>>>>>>>>> using
>>>>>>>>>> system cron. You can check whether the app has been started 
>>>>>>>>>> by
>>>>>>>>>> systems
>>>>>>>>>> cron
>>>>>>>>>> by checking if OC::$CLI is set to true.
>>>>>>>>>> If you want to  use background jobs in your app, you have to
>>>>>>>>>> register
>>>>>>>>>> them
>>>>>>>>>> in appinfo/app.php by calling 
>>>>>>>>>> OCP\BackgroundJobs::addRegularTask(
>>>>>>>>>> $class,
>>>>>>>>>> $method ).
>>>>>>>>>> The first app featuring a background job is the news app 
>>>>>>>>>> being
>>>>>>>>>> implemented
>>>>>>>>>> by Alessandro Cosentino (zimba12). If you want to use 
>>>>>>>>>> background
>>>>>>>>>> jobs in
>>>>>>>>>> your app, have a look at the apps:newsapp repository first! 
>>>>>>>>>> There
>>>>>>>>>> you
>>>>>>>>>> will
>>>>>>>>>> not only find a working example, but also a strategy of how 
>>>>>>>>>> to deal
>>>>>>>>>> with
>>>>>>>>>> the
>>>>>>>>>> different requirements of AJAX/Webcron and the system cron.
>>>>>>>>>> Regards,
>>>>>>>>>>
>>>>>>>>>> Jakob
>>>>>>>>>>
>>>>>>>>>> 1: http://www.easycron.com/