SetByteArrayRegion Behavior
I was wondering if someone could help me understand this better...
I have a large amount of memory generated in a C++ application that I want to make available to my JVM. I'm currently using SetByteArrayRegion() to get the data into my Java object, however I believe that this is making a copy of the data, rather than referencing the shared memory from the C++ application.
Is there a way to simply pass a shared pointer in to the JVM and use it as a byte[]? When I've tried that, I end up with access violations from the JVM.
Thanks.
You should use the [url http://java.sun.com/j2se/1.5.0/docs/guide/jni/spec/functions.html#nio_support]JNI NIO support[/url] (JDK 1.4+).
This very simple example should give you an idea how to use it.// MemAccess.java:
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
public class MemAccess {
static {
System.loadLibrary("MemAccess");
}
public static void main(String[] args) {
new MemAccess().readGeneratedMem();
}
void readGeneratedMem() {
// get a reference to the object that holds a pointer to the c++ buffer
ByteBuffer buffer = getGeneratedMem();
buffer.order(ByteOrder.nativeOrder());
int nbr = 16;
// walk through the c++ buffer to display the values
for (int i = 0; i < nbr; i++)
System.out.println(buffer.getInt());
}
native ByteBuffer getGeneratedMem();
}
// MemAccess.h:
#ifndef _Included_MemAccess
#define _Included_MemAccess
#include <jni.h>
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jobject JNICALL Java_MemAccess_getGeneratedMem(JNIEnv * env, jobject obj);
#ifdef __cplusplus
}
#endif
#endif /* _Included_MemAccess */
// MemAccess.cpp:
#include "MemAccess.h"
JNIEXPORT jobject JNICALL Java_MemAccess_getGeneratedMem(JNIEnv * env, jobject obj) {
int nbr = 16;
int * buffer = new int[nbr]; // c++ buffer
for (int i = 0; i < nbr; i++)
buffer[i] = i * 2;
// return a reference of a (Java) object that holds a pointer to the c++ buffer
return env->NewDirectByteBuffer(buffer, nbr * sizeof(int));
}
Regards
