Building and Running Applications with Java and Native Code on SGI Systems

This document refers to the o32/n32 MIPS ABI's and the green/native threads packages. These concepts, and their associated environment variables and command-line options, are described in MIPS ABI's and Threads.

The description below assumes that you have installed Java in the default location. If you used the -r option to inst or swmgr to install Java in an alternate location, then you should prepend that location to all instances of /usr/java below.

In the sections that talk about building applications, it is assumed that you have installed the necessary subsystems from the java_dev product.

Building Native Code DSO's for Java Applications

For general information on developing applications with native code, and for detailed information on the new Java Native Interface (JNI), see Sun's JNI documentation. An easy way to get started is with our JNI demos. The main points to remember are:

• Compile for the right ABI. Since the default ABI for the SGI C/C++ compilers depends on your version of IRIX, it is best to always use the -o32/-n32 command-line options or to set the SGI_ABI environment variable (it controls these compilers as well as the Java software).
  
  
• Use the right header file directories, /usr/java/include and /usr/java/include/irix.
  
  
• Use the -shared flag to create a DSO.
  
  
• Link against the right libraries (if your code references symbols in them). Library locations depend on the ABI you are using:
  • for o32: /usr/java/lib/sgi/green_threads
  • for n32: /usr/java/lib32/sgi/green_threads

  Note that simply linking against the green threads libraries is fine, regardless of whether the application will be run with green threads or native threads. Use the -l option with the name of any library you need to link against.

For example, if javah produces a stub file HelloWorld.c and you provide native routine implementations in HelloWorldImp.c, you might use the following commands to create an n32 DSO libhello.so:

cc -n32 -I/usr/java/include -I/usr/java/include/irix -c HelloWorld.c
cc -n32 -I/usr/java/include -I/usr/java/include/irix -c HelloWorldImp.c
cc -n32 -shared HelloWorld.o HelloWorldImp.o -L/usr/java/lib32/sgi/green_threads -ljava -Wl,-woff,85 -Wl,-woff,134 -o libhello.so

(the -Wl,-woff,85 -Wl,-woff,134 options simply filter out some harmless warnings that are typical when linking against libjava.so). You could then load this DSO with the Java call:

System.loadLibrary("hello");

Running Java Applications with Native Code

To run a Java application with native code, you need to set your LD_LIBRARY_PATH or LD_LIBRARYN32_PATH (depending on which ABI the native code DSO's were compiled for) as described in setting up your environment to run Java correctly. Then make sure to run java with the correct ABI as well.

To determine the ABI of any object file, DSO, or executable, simply run the UNIX file(1) command on it. For example:

• file libhello.so

If the resulting message begins with "ELF 32-bit", the file is o32. If the resulting message begins with "ELF N32", the file is n32.

Building and Running Invocation API Applications

The Invocation API is a part of Sun's Java Native Interface which allows you to create C/C++ applications with embedded Java virtual machines for running Java code. For more information, see the Invocation API section of the JNI specification under Sun's JNI documentation.

Building a C/C++ application which uses the Invocation API is generally similar to building a native code DSO for a Java application, except that you use the compilers to create an executable instead of a DSO, so you do not need the -shared flag.

Running an Invocation API application is different from running a Java application, however, because what is run is a C/C++ executable rather than one of the Java command scripts. This means that the locations of the system classes and DSO's will not be automatically inserted into your CLASSPATH and LD_LIBRARY_PATH/LD_LIBRARYN32_PATH.

If you have received from another source an Invocation API application which does not account for this, or you want to run (and possibly distribute for others to run) an Invocation API application that you have written, the best way to handle this is to run the program using a script which sets these environment variables properly and then runs the executable. The correct class path fragment to locate all the system classes is

/usr/java/classes:/usr/java/lib/rt.jar:/usr/java/lib/i18n.jar

and the correct DSO locations depend on the ABI and threads package you are using:

• o32/green: /usr/java/lib/sgi/green_threads
• n32/green: /usr/java/lib32/sgi/green_threads
• o32/native: /usr/java/lib/sgi/native_threads
• n32/native: /usr/java/lib32/sgi/native_threads

See our Invocation API demo for an example of how to do this (if you have installed the necessary subsystems from the java_dev product).

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