Using Native C Functions

[Peter]

I have some problems with native functions in HaikuVM.

I have the following simple code example, where i want to make the blink part in C instead of in Java.

package main;

public class Blink {  

    public static native void Main();  

    public static native void nBlink();  

    public static void main(String[] args) {  
        // Data direction of I/O-Port. 
        Main();
        while (true) {  
            nBlink();
        }  
    }  
}  

The functions gets generated in haikuJNI.c as mentioned in the tutorial, e.g.

/*
 * Class:     Blink
 * Method:    Main
 * Signature: ()V
 */
JNIEXPORT void Java_Blink_Main
  (JNIEnv *, jclass);

JNIEXPORT void Java_Blink_Main JNICALL
  (JNIEnv *env, jclass obj)
{
    // TODO: insert your code here
}

/*
 * Proprietary HaikuVM stack to JNI Adapter function.
 * DO NOT EDIT THIS FUNCTION - it is machine generated.
 * 
 * Class:     Blink
 * Method:    Main
 * Signature: ()V
 */
JNIEXPORT void native_Blink_Main_V(void) {
    pushTop();    // Save variable top onto stack.
    {
        jclass     obj = NULL;
        JNIEnv     *env = (JNIEnv*)⊤
        Java_Blink_Main((JNIEnv*)&env, obj);
    }
    popTop();
}

But the block with the "TODO" comment always gets overwritten when compling. What am I doing wrong? I Also tried the @NativeCFunction flag, but it did not generate any functions in nativeCFunctions.cpp

What am I doing wrong, and also have can i use includes in these native functions?

Thanks in advance.

I'm also getting the following error:

./HaikuVM/utility/nativeCFunctions.o: In function `native_Blink_nBlink_V':
nativeCFunctions.cpp:(.text.native_Blink_nBlink_V+0x4): undefined reference to `nBlink'

[genom2]

Hello Peter,

thank you for using HaikuVM.

What you see in 'haikuJNI.c' is a HaikuVM generated blueprint of the JNI wrapper. It's made to copy&past it into some C file of your project directory as stated in this tutorial: http://haiku-vm.sourceforge.net/#[[JNI%20simple]]
(The file 'haikuJNI.c' is not made for compilation with a C compiler. It's just made for you, as a copy&past source and therefore is overwritten/generated on any run of HaikuVM.)

In your case try this.
Make some directory 'firstJNIProject':

mkdir firstJNIProject
mkdir firstJNIProject\myFirstJNIfiles
cd firstJNIProject

Haikufy your Java program:

C:\HaikuVM\bin\haiku --Config duemilanove --classpath C:\myWorkspace\src\main\java C:\myWorkspace\src\main\java\main\Blink.java 

And yes, in this state you get some 'undefined reference' error like:

./HaikuVM/JVM.o:(.progmem.data+0x2d8): undefined reference to `native_main_Blink_Main_V'
./HaikuVM/JVM.o:(.progmem.data+0x2db): undefined reference to `native_main_Blink_nBlink_V'

But now it's happy copy&past time. Copy the part you mentioned from 'haikuJNI.c' into (let's say) file 'firstJNIProject\myFirstJNIfiles\myNativeCFunctions.cpp'. After some additional editing, your C++ file 'myNativeCFunctions.cpp' should look like this:

#include <jni.h>

#ifdef __cplusplus
extern "C" {
#endif

/*
 * Class:     main.Blink
 * Method:    Main
 * Signature: ()V
 */
JNIEXPORT void Java_main_Blink_Main
  (JNIEnv *, jclass);

JNIEXPORT void Java_main_Blink_Main JNICALL
  (JNIEnv *env, jclass obj)
{
    // TODO: insert your code here
}

/*
 * Proprietary HaikuVM stack to JNI Adapter function.
 * DO NOT EDIT THIS FUNCTION - it is machine generated.
 * 
 * Class:     main.Blink
 * Method:    Main
 * Signature: ()V
 */
JNIEXPORT void native_main_Blink_Main_V(void) {
    pushTop();    // Save variable top onto stack.
    {
        jclass     obj = NULL;
        JNIEnv     *env = (JNIEnv*)&top;
        Java_main_Blink_Main((JNIEnv*)&env, obj);
    }
    popTop();
}

/////////////////////////////////////////////////


/*
 * Class:     main.Blink
 * Method:    nBlink
 * Signature: ()V
 */
JNIEXPORT void Java_main_Blink_nBlink
  (JNIEnv *, jclass);

JNIEXPORT void Java_main_Blink_nBlink JNICALL
  (JNIEnv *env, jclass obj)
{
    // TODO: insert your code here
}

/*
 * Proprietary HaikuVM stack to JNI Adapter function.
 * DO NOT EDIT THIS FUNCTION - it is machine generated.
 * 
 * Class:     main.Blink
 * Method:    nBlink
 * Signature: ()V
 */
JNIEXPORT void native_main_Blink_nBlink_V(void) {
    pushTop();    // Save variable top onto stack.
    {
        jclass     obj = NULL;
        JNIEnv     *env = (JNIEnv*)&top;
        Java_main_Blink_nBlink((JNIEnv*)&env, obj);
    }
    popTop();
}

#ifdef __cplusplus
}
#endif

Give it a try:

C:\HaikuVM\bin\haiku --Config duemilanove --classpath C:\myWorkspace\src\main\java C:\myWorkspace\src\main\java\main\Blink.java 

Now all 'undefined reference' errors should be resolved. You are ready to fill the "TODO" comments with your code.

Is this of some help for you?