HP-UX Programmer's Guide for Java 2

Table Of Contents

program using the Java™ method:System.loadLibrary(). The implementation of

this function with the JVM on HP-UX relies upon the HP-UX runtime routine shl_load.

The alignment requirements for Java™ data structures allocated in the JVM are not the

same as those found in the standard PA-RISC 2.0 calling conventions. The JVM requires

that class instance data members 64-bits in size (longs and doubles) be allocated at the

next available 4-byte boundary. The standard PA-RISC 2.0 calling conventions normally

require that such objects be aligned on the next 8-byte boundary. If a C or C++ native

method were to access such a Java™ class instance data member that was not properly

aligned on an 8-byte boundary, a SIGBUS signal would be delivered to the program

and this would terminate the JVM. To prevent this situation, use the +u4 option to the

C and aCC compilers when compiling native that will directly access Java™ data

members. This command-line option instructs the compiler to use a special sequence

when dereferencing pointers to the 64-bit types. The special sequence correctly handles

the cases in which a 64-bit type is misaligned.

When building native method implementations to be used with the kernel-threaded

JVM, sources must be compiled with the following additional command-line option:

-mt

Additionally developers who produce hybrid applications where the application entry

point is a language other than Java, for example a C language main(), must link with

the p-thread library using -lpthread on the link line in order to use the

kernel-threaded JVM. Failing to link with libpthread.sl (libpthread.so on

Integrity) will result in an runtime failure when the JVM is loaded. The libpthread

library was not available in releases prior to HP-UX 11.0.

Implementers of native methods called by Java™ main programs should take care to

insure that null pointers are not dereferenced. The JVM is linked using the -z option,

which is discussed in the man page for the C compiler. If a native method does deference

a null pointer a SIGSEGV will be delivered to the JVM and this will cause the JVM to

terminate.

HP provides the following two Java™ examples on how to call C and C++ from Java™

using the standard JNI calling mechanism. Code examples C++ for Java™ 1.3.1 and

1.4.2 follow.

Sample code for SDK 1.3.1

Sample Java™ calling native method implementation in C

Here is the sample Java™ program that calls a native method, which has a C

implementation:

// File TestJava2CallingNative.java

class TestJava2CallingNative {

native static void sayHelloWorld();

Java™ calling a native (non-Java) method 47