[QGIS-Developer] [processing] launching separate process/thread

[Andreas Plesch]

Hi Giovanni,

thanks for the pointer. When I use multiprocessing.Process instead of
threading.Thread I get:

PicklingError: Can't pickle <function webserver at 0x1622F330>: it's not
found as __main__.webserver

This is probably related to:

https://docs.python.org/2/library/multiprocessing.html#windows

So I am not sure how one would use multiprocessing from a processing script
rather than from the __main__ python program.

-Andreas


On Sun, May 21, 2017 at 8:45 AM, G. Allegri <giohappy at gmail.com> wrote:

> Side note: multiprocessing is part of the Python standard library.
> https://docs.python.org/2.7/library/multiprocessing.html
>
> Giovanni
>
> Il 21 mag 2017 14:18, "Andreas Plesch" <andreasplesch at gmail.com> ha
> scritto:
>
>> As a followup, here is the simple processing script which is my attempt
>> at launching a separate task:
>>
>> https://github.com/andreasplesch/QGIS-X3D-Processing/blob/
>> master/scripts/launch_webserver.py
>>
>> qgis2web does not seem to need a real http server for the preview as
>> openlayers apparently can use the file protocol.
>>
>> -Andreas
>>
>> On Sat, May 20, 2017 at 5:29 PM, Andreas Plesch <andreasplesch at gmail.com>
>> wrote:
>>
>>> I would like to launch a minimal web server from a processing script to
>>> serve html properly (rather than using the file protocol).
>>>
>>> Since the web server needs to run and keep running separately from qgis
>>> or the qgis python interpreter, I investigated various ways to accomplish
>>> this using SimpleHTTPServer. On windows 2.18.7 as linux should be more
>>> robust.
>>>
>>> - threading.Threat : start() works until the server actually serves a
>>> file. Then qgis crashes with a minidump . For some reason, the crashing
>>> happens not always but more often than not.
>>> - multiprocessing : seems to be the recommended solution but I do not
>>> seem to have it with Qgis python (?)
>>> - QProcess.start() : works from the python terminal, seems robust but
>>> does not seem to work from a processing script (?). Would be the preferred
>>> solution.
>>> - QProcess.startDetached('python',(args),dir) : works reliably but
>>> requires killing and restarting the process to change the root directory
>>> served
>>>
>>> This may all change with Qgis 3 but I suspect 2.18 will be around for a
>>> while, too.
>>>
>>> Any recommendations or ideas would be welcome.
>>>
>>> I will look into qgis2web to see what it does.
>>>
>>> --
>>> Andreas Plesch
>>> 39 Barbara Rd.
>>> Waltham, MA 02453
>>>
>>
>>
>>
>> --
>> Andreas Plesch
>> 39 Barbara Rd.
>> Waltham, MA 02453
>>
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>


-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
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