Re: serial comm. with rxtx, GPSExplorer, and GCJ -- runtime exception

[David Daney <ddaney at avtrex dot com>]

Michael Mohr wrote:
> On Wed, 24 May 2006 10:26:05 -0700
> David Daney <ddaney@avtrex.com> wrote:
>
>
> > Michael Mohr wrote:
> >
> > > Hello,
> > >
> > > I'm currently attempting to use GCC 4.1's gcj to compile a medium-sized (6000-line) java application.  Unfortunately, it requires raw access to serial ports, as implemented by RXTX.  It appears that RXTX has already been modified to compile using CNI; however, the port appears to be in early alpha stage.
> > >
> > > I am able to compile RXTX (mostly) without complaint.  I am also able to compile my application -- GPSExplorer -- with no warnings or errors using GCC 4.1.  However, it exits when run with the following exception:
> > >
> > > Exception in thread "main" java.lang.UnsupportedOperationException
> > >   at gnu.java.awt.peer.gtk.GdkGraphicsEnvironment.getAllFonts (lib-gnu-java-awt-peer-gtk.so)
> > >   at GPSExplorer.<init> (GPSExplorer)
> > >   at GPSExplorer.main (GPSExplorer)
> >
> > Looks like GraphicsEnvironment.getAllFonts() is not supported by your 
> > libgcj.
>
>
> Okay.  Is there a person who I could contact that is working on related classes?  I'd be happy to lend a hand, at least in regards to implementing functions missing from my own application.

The classpath project is the source of the culpable code.  See 
http://www.gnu.org/software/classpath/

> > > The program makes use of the AWT and Swing classes.  It runs perfectly under any JVM after 1.2 (and probably before, but I haven't tested that far back).  I compile and link GPSExplorer as follows:
> > >
> > > rm -f *.o *.s GPSExplorer
> > >
> > > for x in *.java
> > > do
> > >  gcj -classpath .:$PWD/RXTX/RXTX.jar -c $x
> > > done
> > >
> > > gcj *.o -L$PWD/RXTX -lrxtx -o GPSExplorer --main=GPSExplorer
> > >
> > > As I see it, there are 3 possibilities:
> > >  o Something is wrong with the app in question, GPSExplorer
> >
> > Perhaps.
> >
> >
> > >  o Something went wrong with the CNI RXTX port
> >
> > Again, perhaps, but that is not the problem you are seeing.
> >
> >
> > >  o Something isn't right with GCJ
> >
> > Yeah.  The AWT support is not complete yet.
>
>
> I figured that, but I didn't want to seem pretentious by stating that there was a problem with GCJ.  There may still be problems with GPSExplorer under GCJ, but as of yet this is the most visible issue.  Incidentally, why was I able to compile and link GPSExplorer if a used function was not available?

Many methods are stubbed out so that you don't get compile time errors. 
 That this is a good thing is up for debate.

> > > The text of the error leads me to Door #3, but I could be very wrong.  This is my first attempt to compile a large Java application using GCJ.
> > >
> > > Here's the output of gcc -v:
> > > Using built-in specs.
> > > Target: i686-pc-linux-gnu
> > > Configured with: /var/tmp/portage/gcc-4.1.0-r1/work/gcc-4.1.0/configure --prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.0 --includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.0/include --datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0 --mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0/man --infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0/info --with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.0/include/g++-v4 --host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec --enable-nls --without-included-gettext --with-system-zlib --disable-checking --disable-werror --disable-libunwind-exceptions --disable-multilib --disable-libmudflap --disable-libssp --enable-java-awt=gtk --enable-languages=c,c++,java,fortran --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
> > > Thread model: posix
> > > gcc version 4.1.0 (Gentoo 4.1.0-r1)
> > >
> > > When I enable -Wall, I get hundreds of warnings, all of which are either:
> > >   o warning: Discouraged redundant use of 'public' modifier in declaration of abstract method 
> > >   o warning: An empty declaration is a deprecated feature that should not be used.
> > >
> > > Other than those two errors, nothing is reported.  This is the contents of GPSExplorermain.i after the final link with -save-temps:
> >
> > Then don't enable -Wall.
>
>
> I'm perfectly aware that I can choose not to enable -Wall.  I was following precisely the directions given for filing a bug report, which state at http://gcc.gnu.org/bugs.html :
>
> "Before reporting that GCC compiles your code incorrectly, please compile it with gcc -Wall and see whether this shows anything wrong with your code that could be the cause instead of a bug in GCC."
>
> I wanted it to be clear that I had read the directions and was following procedure.

Right, good point.

David Daney