[Qgis-developer] [GRASS-dev] GRASS & QGIS: the future

[Radim Blazek]

On Fri, Apr 18, 2014 at 2:19 PM, Sören Gebbert
<soerengebbert at googlemail.com> wrote:
> Hi Radim,
> IMHO we GRASS developers are  too stubborn to change the design of
> GRASS GIS to work as library with persistent applications. This would
> require rewriting plenty of core functionality and modification of all
> C-modules. But there is a solution for persistent applications, called
> Remote Procedure Call (RPC), more below.

It sounds interesting but it seems to be a huge work an far future. I
am also concerned about complexity, e.g. starting / keeping running
servers on various platforms. I can imagine endless bug reports about
"server not running". I am looking for something which will not
require permanent assistance. It is not KISS enough for me.

Radim

> 2014-04-18 11:31 GMT+02:00 Radim Blazek <radim.blazek at gmail.com>:
>> I have upgraded  the vector provider to GRASS 7, layers may be added
>> by drag from browser. The raster and the plugin are disabled. Be
>> careful about multiple versions on the same system
>> (LD_LIBRARY_PATH..., check with ldd if does not work).
>>
>> Unfortunately GRASS 7 moved ahead towards its aim "to make life harder
>> for anyone trying to use the GRASS libraries" [1]. Basically more and
>> more low level functions are calling exit() instead of returning error
>> code if something failed. As I am not willing to implement GRASS
>> module call for each simple function, we have to think again about
>> hacks we can use:
>>
>> 1) add a requirement that GRASS 7 used with QGIS must be compiled with
>> -fexceptions
>>
>> 2) add a requirement that a patch (it is a single line comment in
>> fact) must be applied to GRASS 7 to make it usable with QGIS
>>
>> 3) use setjmp()/longjmp()
>>
>> 4) let QGIS crash whenever GRASS lib function fails
>
> I fear that none of these suggestions are good working solutions,
> since in case a fatal error or a segfault occurs nothing (no
> exception, no setjmp) will prevent QGIS from crashing. So i would like
> to suggest the following:
>
> 5.) Using a RPC interface for map metadata, vector and raster map
> access. Hence one or several GRASS "server" processes provide an RPC
> interface to access GRASS library functions that are needed in a
> persistent application. Most important is the vector editing, vector
> reading/writing, database access, raster reading and map metadata
> support. Everything else can be done using modules. Hence the RPC
> interface will support only a limited subset of the GRASS library
> functions. This RPC interface should only be used in the GRASS
> provider classes, the GRASS plugin itself can be written in C++ or
> Python.
>
> This approach will decouple GRASS from QGIS, since all communication
> is done via Inter Process Communication (IPC) using pipes or sockets.
> There is no need anymore to catch a fatal error or to link GRASS
> libraries directly to QGIS. The GRASS plugin can be implemented GRASS
> version independently and so the GRASS data provider, since they will
> not use GRASS functions directly only the RPC interface. The RPC
> implementation on the side of GRASS will provide a consistent
> interface that will not change in case the underlying GRASS API
> changes.
>
> I strongly suggest to use an existing RPC framework to implement fast
> binary data exchange and the IPC. My favorite is apache thrift[1],
> since it supports plenty of programming languages (C/C++, Python,
> Java, JavaScript, ...) and provides operating system independent
> client and server functionality. It supports exceptions on client side
> that can be emitted in case a GRASS server process died because of a
> fatal error, SIGINT or segfault.
>
> I am absolutely willing to implement the RPC server side in GRASS
> using thrift and C++, providing plenty of Python unit tests that show
> howto use it on the client side. We just need to decide what kind of
> GRASS library functionality is needed as RPC interface and what can be
> done in QGIS with C++/Python directly (gisrc creation, GRASS
> environmental variable settings, ...) or using GRASS modules
> (g.region, g.gisenv, ...).
>
> [1] https://thrift.apache.org/
>
>
> Best regards
> Soeren
>
>>
>> Radim
>>
>> [1]https://trac.osgeo.org/grass/ticket/869#comment:1
>>
>> On Thu, Mar 27, 2014 at 11:18 AM, Paolo Cavallini <cavallini at faunalia.it> wrote:
>>> Hi all.
>>> I learned during dinner that GRASS7 RC1 is due very soon. This opens the
>>> issue of its functioning in QGIS. IMHO:
>>>
>>> * the qgis-grass-plugin might stop working (this has to be tested)
>>> * some of the module options will be different
>>> * new modules will not be available in QGIS.
>>>
>>> I think we can deal with this in several ways:
>>>
>>> * dropping the plugin, and concentrate the work on Processing
>>> * upgrading both the plugin and Processing.
>>>
>>> In the first case, we have two major issues:
>>>
>>> * upgrading Processing GRASS modules
>>> * changing the current Processing behaviour, avoiding the import-export
>>> phase when piping consecutive GRASS commands; this makes GRASS modules
>>> slower than the equivalent commands of other backends.
>>>
>>> While the first issue can be solved easily by a couple of people in a
>>> few days, the second one is more tricky, and requires hard coding skills.
>>> In addition, we'll no longer be able to edit GRASS vectors directly.
>>>
>>> In the second case, we'll have more work, and a not-so-nice duplication.
>>>
>>> I would like to have an open discussion on this, avoiding things to just
>>> happen, with the possible negative consequences.
>>>
>>> All the best.
>>> --
>>> Paolo Cavallini - www.faunalia.eu
>>> QGIS & PostGIS courses: http://www.faunalia.eu/training.html
>>> _______________________________________________
>>> grass-dev mailing list
>>> grass-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-dev
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