[Paraview] Invoke remote procedure from proxy with argument and return value

[Utkarsh Ayachit]

Mario,

You can definitely add a new utility VTK class that wraps this logic
and then wrap it and call that from Python. Don't go about trying to
wrap vtkClientServerStream, however. That may be a dead end.

Utkarsh

On Wed, Dec 14, 2016 at 2:31 PM, Mario Schreiber
<schreibermario40 at gmail.com> wrote:
> Thank you for your kind reply, Utkarsh.
> The C++ example clarifies many of the details that I couldn't find explained
> anywhere.
>
> I will try to wrap the missing parts in python, because we can't afford to
> migrate the rest of our application to C++.
> Just asking, before I waste my time with a bunch of problems that you know
> in advance that cannot be solved: Is there any reason why the steps you
> showed cannot be wrapped in python, or has it "just not been done, yet"?
>
> Thanks
> Mario
>
>
> 2016-12-13 18:54 GMT+01:00 Utkarsh Ayachit <utkarsh.ayachit at kitware.com>:
>>
>> Mario,
>>
>> Firstly, there's no way from Python to do what you want to do except
>> using the property mechanism, since well, the goal with ParaView was
>> not to provide a general purpose RPC framework. In C++, you can do
>> that you want as follows:
>>
>> vtkSMProxy* proxy = ...
>> std::string arg = ...;
>> vtkClientServerStream stream;
>> stream << vtkClientServerStream::Invoke
>>             << VTKOBJECT(proxy)
>>             << "doSomething" << arg.c_str()
>>             << vtkClientServerStream::End;
>>
>> vtkSMSession* session = proxy->GetSession();
>> session->ExecuteStream(
>>    /*location*/ proxy->GetLocation(),
>>   /* ignore_errores*/ false);
>>
>> vtkClientServerStream result =
>> session->GetLastResult(proxy->GetLocation());
>> if (result.GetNumberOfMessages() == 1 && result.GetNumberOfArguments(0) ==
>> 1)
>> {
>>    std:string aresult;
>>   result.GetArgument(0, 0, &aresult);
>> }
>>
>> Utkarsh
>>
>>
>>
>> On Sun, Dec 11, 2016 at 12:01 PM, Mario Schreiber
>> <schreibermario40 at gmail.com> wrote:
>> > Why is it so complicated to call a procedure and receive a return value
>> > on
>> > the client?
>> >
>> > I am attaching my attempt (CMakeLists.txt, vtkSquareFun.cxx,
>> > vtkSquareFun.h
>> > and TestPlugin.xml, each less than 20 lines of code), which basically
>> > calculates the square of an argument in vtkSquareFun::eval(double x).
>> >
>> > When I load this plugin in Paraview and open the Python Shell, I can
>> > evaluate vtkSquareFun::eval() using a detour by first setting the
>> > argument
>> > and then getting the result, which is linked to the argument property in
>> > TestPlugin.xml:
>> >
>> > fun=servermanager.CreateProxy("test","SquareFun")
>> > fun.GetProperty("Arg").SetElement(0,999)
>> > fun.UpdateVTKObjects()
>> > fun.UpdatePropertyInformation()
>> > fun.GetProperty("Result").GetElement(0)
>> > ... showing the correct result 998001.
>> >
>> > Why can't I simply run the following?
>> > fun=servermanager.CreateProxy("test","SquareFun")
>> > result=fun.InvokeCommand("eval",[999.0])
>> >
>> > Does Paraview really not provide any means of calling a function with
>> > arguments and return value within a single client-server communication?
>> > All
>> > these individual message transfers are a bottleneck in our application.
>> > Does
>> > the Paraview architecture exclude more universal remote procedure calls,
>> > or
>> > do you think that one could just augment the available procedures with
>> > another procedure that can deliver a set of custom return values?
>> >
>> > Thanks
>> > Mario
>> >
>> >
>> > 2016-12-07 7:34 GMT+01:00 Mario Schreiber <schreibermario40 at gmail.com>:
>> >>
>> >> Hello,
>> >> I have a use case, where a vtkObject on the server implements a method
>> >> like
>> >>
>> >> std::string doSomething(std::string arg);
>> >>
>> >> Now, with a proxy prx on the client for  that class, I would like to
>> >> call
>> >> the remote procedure similar to
>> >>
>> >> result=prx.InvokeCommand("doSomething",[arg])
>> >>
>> >> Is something like this possible?
>> >> I found a very complicated workaround by first defining the arguments
>> >> as
>> >> properties, defining the result as information_only property linked to
>> >> on of
>> >> the args, then calling "UpdateVTKObjects" to push the arguments and
>> >> finally
>> >> "UpdateInformationProperties" to pull the result. Is there an easier
>> >> solution, possible with a short example?
>> >>
>> >> Thank you
>> >> Mario
>> >
>> >
>> >
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