Re: Django and asynchronous tasks

Hi All

I spent several days reading and searching examples of how to implement channels. The current status of my project is as follows:

• I have a page which lets the user enter the data used for the offline calculations, a POST request is send
• the post request is handled and I can forward these data to a rq-worker, after which I open a basic web-page showing the input data. This page should also hold the results of the asynchronous calculations
• the rq-worker starts the requested download of data from a site and I store the data in the apps (gnsspredict) directory. The rq-worker stops with a success reported in the log.
• not yet implemented, but this is similar to the download thread, I shall further launch 2 to 3 workers to split up the work so that I can inform the user of the progress of the async calculations

But this is where I do not know what to do next.

As far as I understand 

• the rq-worker can send its results using a dictionary to a 'reply-channel', but where does this channel goes to? 
  
• of the few complete working examples on github I found I assume that I have to write a javascript (which I never used) to treat the results from the worker thread? I also remark that the javascript has as name 'function()', is this always the case? If so, for all 3 to 4 workers how do I write a script that takes action on which asyn cthread that has finished?

All help is appreciated

Thanks

Alain

On Thursday, 10 November 2016 11:55:01 UTC+1, ludovic coues wrote:

Websocket provide a way for server to send information to the client
without waiting for input from the client.

Django channels [1] is a project to bring native support of websocket
to django. There are alternatives which might involve a bit more of
work

[1] https://channels.readthedocs.io/en/stable/

2016-11-10 11:38 GMT+01:00 Antonis Christofides <ant...@djangodeployment.com>:
> Is there no mechanism that when the background tasks finishes to have a web
> page called which could display the results?
>
> Web pages cannot be "called". They are loaded by the browser. So, what you
> want is a mechanism that notifies the browser that an event has occurred in
> the server. That mechanism is comet.
>
> Antonis Christofides
> http://djangodeployment.com
>
> On 2016-11-10 11:54, Alain Muls wrote:
>
> Hi
>
> Tx for the suggestion but how do I reload a page after eg 30 seconds?
> Is there no mechanism that when the background tasks finishes to have a web
> page called which could display the results?
> I had a look at the signal mechanism of Django but I think that is not
> working since the background task is in another environment than the django
> apps which called it.
>
> bye/alain
>
> On Thursday, 10 November 2016 09:55:08 UTC+1, Antonis Christofides wrote:
>>
>> (Note: The most popular way to do asynchronous tasks is celery, but indeed
>> some
>> people prefer django-rq, which is said to be simpler. But your question is
>> not
>> affected by that.)
>>
>> I'm not an expert but I think that the "correct" way to do what you want
>> would
>> be to use comet (i.e. the opposite of ajax). However, if the work required
>> to
>> make that work is not justified by the budget or the business case, you
>> might be
>> able to get away with a message like "This information is being
>> (re)calculated.
>> Reload the page after half a minute to view the updated results." (That's
>> what I
>> did last time :-)
>>
>> Regards,
>>
>> Antonis
>>
>> http://djangodeployment.com
>>
>> On 2016-11-10 10:04, Alain Muls wrote:
>> > Hi All
>> >
>> > I am building a website which makes calculations about the visibility of
>> > satellites. These calculations take about half a minute so I do not want
>> > to
>> > block the site during this time. I found django-rq and was able to start
>> > a
>> > asynchronous task which handles the calculations.
>> >
>> > The problem I have is how do I find out when the calculations of the
>> > task
>> > thread are done so that I can direct the results to another web page
>> > which
>> > will display them?
>> >
>> > Thanks for your help
>> >
>> > Alain Muls
>> >
>> >
>>
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Cordialement, Coues Ludovic
+336 148 743 42

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