When user registers, an email is sent to user after 20 seconds. Is this possible to code with sleep() in moodle.
sleep(20);
if (!send_confirmation_email($user)) {
print_error('noemail','core_email');
}
The sleep will be fairly poor UX and block the session. An adhoc task is the right way to go as DerKanzler said.
As of https://tracker.moodle.org/browse/MDL-66925 you can run the adhoc tasks in keep alive mode and they will process continuously as a psuedo daemon:
php admin/cli/adhoc_task.php --keep-alive=60 --execute
If you still wanted the email to be sent roughly 20 seconds into the future, when you use the Task API to queue the task you can set the future time that it should run:
https://docs.moodle.org/dev/Task_API#Set_a_task_to_run_at_a_future_time
Either way this sounds like a terrible idea to force a user to either way in their browser for 20 seconds, or to wait reloading their email client for 20 seconds. I'd strongly recommend against it.
If you want to do it the 'hacky' way and patch some core files sleep(seconds) is indeed the easiest way to go.
If you are writing a plugin, you can have a look at the Task API, especially at defining AdHoc Tasks. Though this will not execute until your cron job is fired. So you would have to lower your cron execution time limit. Besides that there is currently no option to do this with the moodle API.
Related
I have an MVC web site, a storage queue and a WebJob. Users can request the generation of a set of reports by clicking a button on the web page. This inserts a message into the storage queue. In the past, the WebJob ran continuously and processed those requests fine. But the demand and size of the reports has grown to the point where the WebJob is slowing down the web app. I would like to still place the request message in the queue, but delay processing of all requests until the evening, when the web app is mostly idle. This would allow me to continue using the WebJob code and QueueTrigger functionality without having to waste resources by moving to a dedicated Worker Role, etc. The reports don't need to be generated immediately, so a delay is acceptable.
I don't see a built-in way to set a time window on processing. The only thing I have found is a powershell cmdlet for starting and stopping WebJobs (Start-AzureWebsiteJob / Stop-AzureWebsiteJob). So I was thinking that I could create a scheduled powershell job that runs at midnight, starts the webjob, lets it run, and then runs again early in the AM and stops it.
Does anyone know of a better option than this? Anything more "official" that perhaps I could not find?
One possible solution would be to hide the messages in the queue for a certain amount of time when they are inserted.
If you're using AddMessage method, you can specify this timespan value in initialVisibilityDelay parameter.
What this will do is ensure that the messages are not immediately visible in the queue to be picked by WebJob and will become visible only when this timespan elapses.
Will such a solution work for you?
Maybe I didn't fully understand your question, but couldn't you use "Triggered" WebJob that is triggered by CRON schedule? You can then limit it to specific hours
0 * 20-22 * * *
This example will run every minute from 8pm to 10pm
I have recently been thinking about possible architecture for a simple task reminder system. User will schedule a task and reminder in form of SMS/email/android needs to be sent to all stakeholders at some x minutes before the task is scheduled to be performed(much in the same way google calendar works). The problem here is to send the reminder at that precise point in time. Here are the two possible approaches I can think of:
Cron: I can setup a cron to run every minute. This will scan the table for notifications which need to be sent in the next minute and simply sends the notifications. But, precision is lost as there is always the chance of that +/-1 min error.
Work Queues: I can simply put a message with appropriate delay in a queue at the time task was scheduled. Workers will send the notification as and when they receive the message. I can add as many workers as I want in case my real time behavior starts getting affected because of load. There are still a few issues. How to choose the appropriate work queue? I have evaluated RabbitMq and Beanstalk. While Rabbitmq follows standard AMQP protocol and is widely suggested, it doesn't provide the delay functionality out of the box. There are ways to simulate this using dead-letter-exchanges but this will not work in my case because the delay needs to be variable. Beanstalk supports this but the problem is that beanstalk queue resides entirely in memory which I don't like(but can live with). Any possible alternatives?
Third Approach: ??????. I am sure a simple desktop notification tool does neither of the two. What technology do they use to achieve the same thing?
We had the same scenario and we use Redis for long schedules even now reminders for up to 2 years. You can use Sorted Set where the timestamp is the score.
We use Beanstalkd delay jobs for those kind of reminders where we know it's relatively short term couple of hours, and there is no cancellations, as removing from beanstalkd a delayed message you need to retain the job id in a database for later removal, and that is no viable.
Although you mention memory limit, we use persistence on both Redis/Beanstalkd
I am going to use Laravel 4 queues and integrate them with Iron.io
All of that is pretty straight forward, and I dont think I am going to have problems with that.
Thing that interests me is what is the best way to get status once task is completed?
Iron.io is going to do return call to my server to trigger job, and once that job completes I need to notify user about that...
How could I store this responses, and still be aware of job its related to, because there will be number of different job types?
I would like to hear how did you implement this.
Thanks
As Joseph pointed out in the comments, you'll need to:
Hopefully have a job quick enough for it to be finished when a user is still in browser
Use some sort of way to PUSH data back to your web browser.
The popular methods are:
Websockets
Server-sent events
Long polling - with ajax
I'm trying to implement a basic but flexible "event queue" so that my web app can go run subs asynchronously. The way I have working for me now is the app writes a record to an "event queue" table in my database with info on what to do and when to fire. Then I have a daemon script that queries that table periodically and if something needs to be done, it fires it off.
I'd like to start moving towards watchers using something like AnyEvent or EV so I'm not hitting my database so often, but try as I might, I can't find good info on "best practices" for setting something like this up. AnyEvent's documentation is pretty good, but it seems to assume you know how your events should be passed around...which I don't.
What should my watcher be watching? A file? If so, what should be in that file? I don't need to send a whole bunch of data around, I just basically need something that says, "go off and run this sub right now"
I would greatly appreciate someone pointing me in the right direction.
EDIT:
It's been requested that I be more specific: The events I'm trying to fire are various. Sometimes it's an email that needs sending, sometimes it's some DB work, sometimes I just need an action to be delayed for a few hours or days. In all cases, I have some sort of backend script to handle the action, I just need a way for my frontend (web app) to tell my backend, "hey I need you to go do this in x minutes" or "I need you to do this now"
You might look at Mojolicious which is built to be non-blocking and respond asynchronously. It even uses EV internally if you have it installed. To get started read the doc for Mojolicious::Lite and then the Guides (in order) from here: http://mojolicio.us/perldoc
So what is it that you are actually trying to do? Until you describe what it is you actually need, I can't help you any further that that.
There are some CPAN modules in order to run asynchronous tasks via message queues. Examples:
Queue::DBI
POE::Component::MessageQueue
Any::MQ
I'm looking for a lightweight system that will let me queue up a one-off (non-recurring) task and have it execute at a specific time in the future.
This is for the backend of a game where the user does tasks that are time-based. I need the server to check the status of the user's "job" at the completion time and perform the necessary housekeeping on their game state.
I'm somewhat familiar with Redis, Celery, Beanstalkd, ZeroMQ, et al., but I haven't found any info on scheduling a single unit of work to be executed in the future. (or pop off the queue at a set time) Celerybeat has a scheduler for cron-type recurring tasks, but I didn't see anything for one-off.
I've also seen the "at" command in *nix, but I'm not aware of any frontend for it that can help me manage the jobs.
I realize there are some easy solutions such as ordering keys in Redis and doing a blocking pop, but I'd like to not have to continuously poll a queue to see if the next job is ready.
The closest I've found is the deferred library on GAE, but I was hoping for something that runs on my own Linux box along with my other components.
I'd appreciate any suggestions!
Celery allows you to specify a countdown or an ETA at the call of a task to be executed.
The documentation says it best:
http://docs.celeryproject.org/en/latest/userguide/calling.html#eta-and-countdown