RE: [Plplot-devel] How can java be told permanently about where to find libplplot(d)?

[Alan W. I. <ir...@be...>]

On Mon, 12 Nov 2001, Geoffrey Furnish wrote:

> Alan W. Irwin writes:
>  > I agree there is nothing we can do with libplplot.  What I am asking is
>  > whether there is a mechanism *under java* (some additional command in
>  > PLStream.java or some javac option) which allows java to find libplplot (or
>  > any other C extension library) when it is installed in a non-standard place.
>  > I would be surprised and disappointed if java relied solely on
>  > LD_LIBRARY_PATH to solve this problem.
>
> Well, it's not anything special to java.  We're just talking about the
> semantics of dlopen(), which all programs use to load .so's.

From what you have found out about dlopen, it looks like you can do anything
with it.  Thus, looking at this from the java level, java is free to do
anything before the low-level call to dlopen.  So it really becomes a
question of how java integrates the specification of library names using
System.loadLibrary with their treatment (if any) of the library path.

I did try your suggestion of using an absolute path as part of the library
name. (That is quite easy to do in a configurable way by making the
appropriate modification to config.java which in turn is accessed by the
System.loadLibrary call in PLStream.java.) Alas, this idea did not work. The
run time error was as follows:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Directory
separator should not appear in library name:
/home/software/plplot_cvs/HEAD/plplot/tmp/plplotd

So apparently there is some name interpretation going on before the dlopen
call, and as part of that interpretation java insists the path must not be
part of the name specified to System.loadLibrary.

Of course, this still leaves wide open the question about whether there
might be some alternative mechanism in java to specify the path part of the
name since java can do anything it likes before the dlopen call. Thus, what
I am looking for is the java analog of the python sys.path.insert() function
that we use in pythondemos.py to manipulate the path where python looks for
plmodules.so. Unfortunately, I am now stuck because I don't know how to
search for such functionality in the enormous number of java functions that
are available. Geoffrey, are you aware of a general site where I could
specify say "library path" as a search string and it would find all the java
functions that have something to do with the library path?  The java
tutorial does have a search engine so I tried that, but all it came up with
was the LD_LIBRARY_PATH idea.  I suppose it is possible that java has no way
to specify the library path other than LD_LIBRARY_PATH, but that is quite
limited compared to the sys.path.insert() function available for python.

Alan