RE: [OctDev] [Changeset] Re: Java calling Octave via JNI

[Martin.Hepperle]

Hello all,

after some further experimentation I have given up this route.
I guess that there is some version conflict between C++ runtime
DLLs which I could not resolve.  My DLL was able to load the 
octave DLLs, but when Octave tried to load its .oct libraries,
which seem to be DLLs under Windows, it was unable to load
them with LoadLibrary() ("cannot find library..., but the 
complete path is given, correct and the .oct library is there). 
I was using VS 2005 for my C-Java interface DLL which should be 
compatible with the Octave DLLS, but it may be that there is a 
conflict with differenr runtime libraries. 
I did not want to recompile the whole Octave system.

So I switched to the less elegant but workable way of running
octave.exe and connecting to its stdin and stdout streams.
For this I have replaced my test implementation with the basic
but well structured solution from the packages dk.ange.octave
which I had found at https://launchpad.net/javaoctave.

Thank you for your help,
Martin


-----Original Message-----
From: Jaroslav Hajek [mailto:address@hidden 
Sent: Wednesday, September 10, 2008 1:14 PM
To: John W. Eaton
Cc: David Bateman; address@hidden; Hepperle, Martin;
octave maintainers mailing list
Subject: Re: [OctDev] [Changeset] Re: Java calling Octave via JNI

On Tue, Sep 9, 2008 at 7:44 PM, John W. Eaton <address@hidden>
wrote:
> On  5-Sep-2008, David Bateman wrote:
>
> | David Bateman wrote:
> | > MartinHepperle wrote:
> | >> Hello all,
> | >>
> | >> again this nasty Java -> Octave connection.
> | >>
> | >> I also want to embed Octave into a Java program and call Octave 
> | >> functions from Java.
> | >>
> | >> Initially I started with programming an execution engine which 
> | >> starts octave.exe and connected to its standard input and output 
> | >> pipes. This concept works (in the meantime I also found two 
> | >> solutions which implement the same technique) but is somewhat 
> | >> ugly and inefficient due to conversions to and from strings
> | >>
> | >> What I tried now was to call the Octave DLLs (Windows platform) 
> | >> directly via a C wrapper and using JNI.
> | >> This technique provides a very elegant solution and I have used 
> | >> this in the past to call C and FORTRAN codes from Java. I want to

> | >> define some global variables, set the values from Java, execute 
> | >> some user supplied functions and finally return the results 
> | >> (global variables set inside the user
> | >> functions) to Java.
> | >>
> | >> Now with the Octrave DLLs I stumbled across a problem.
> | >>
> | >> To study the interface to ther DLLs I started with a C++ program.
> | >> Basically I used the following logic:
> | >>
> | >> //-----------------------------
> | >> // start and initialize Octave (once, then keep it alive) char * 
> | >> pArgs[] = {"octave.exe","--path", "C:\\Programme\\Octave", 
> | >> "--norc", NULL}; int iRet = octave_main (4 pArgs, true);
> | >>
> | >> //-----------------------------
> | >> // execute some commands
> | >> std::string s = std::string("global Output;\nglobal 
> | >> Input;\nInput=12;\nOutput=2*Input;\n");
> | >> octave_value x = eval_string (s, false, parse_status); // examine

> | >> the returned "x" with x.isnumeric() etc. works when code is in an

> | >> executable (.exe) file
> | >>
> | >> // what does the follwing code do? It works, but where is the 
> | >> variable in Octave?
> | >> set_global_value (std::string(cName), val); octave_value vReturn 
> | >> = get_global_value (std::string(cName)); // the variable has the 
> | >> correct value, but is_globally_visible
> | >> (std::string(Name)) returns false...
> | >> // what does global mean here?
> | >>
> | >>
> | >>
> | >> // terminate Octave
> | >> do_octave_atexit();
> | >> //-----------------------------
> | >>
> | >> All this works well when I have the code inside an executable C++

> | >> program (MSVC8.0).
> | >>
> | >> So far so good.
> | >>
> | >> Now for the interface via JNI I have to put this into a DLL which

> | >> provides a thin layer between Java objects and the C interface to

> | >> Octave.
> | >> If I put the same code inside a DLL I can initialize Octave, but 
> | >> the eval_string () and other functions doe not work - they seem 
> | >> to do nothing. I found can do somethings with set_global_value ()

> | >> and get_global_value (), but this is not enough and also these 
> | >> "global" values seem to be something else than global variables 
> | >> in Octave.
> | >>
> | >> Anyway, I see that eval_string() seems to work when called from a

> | >> C executable, but not when I call it from a DLL. Could this have 
> | >> something to do with i/o streams which are different in a DLL and

> | >> in an EXE?
> | >>
> | >> Any ideas where to look and how to test?
> | >>
> | >>
> | >> Thank You,
> | >>
> | >> Martin
> | >>
> | >>
> | >>
> | >>
> | >>
> | > eval_string can only work if the interpreter is initialized.. 
> | > Check the mailing lists for how to initialize the interpreter.
> | >
> | > D.
> | >
> | >
> | Seeing as how this question has come up a number of times, I suggest

> | the attached changeset that adds an example of how to initialize the

> | interpreter and use it from a standalone application.
>
> I applied it.
>

I transplanted this "explanationation" (hg description :-) patch to
3.0.x series




--
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU) Prague, Czech Republic
url: www.highegg.matfyz.cz