JNI学习2

简单的ByteBuffer调用和使用MPI交换参数

程序设计：用ByteBuffer.allocateDirect() 接口分配两个等长的内存空间（addr1和addr2），在JNI中使用GetDirectBufferAddress接口获得两个内存空间的地址，通过MPI的MPI_Isend/MPI_Recv接口，将addr1中的数据传递到addr2中。整个MPI在单进程中执行。

ByteBuff.java

import java.nio.ByteBuffer;

public class ByteBuff {

    static {
        System.loadLibrary("buff");
    }

    public native void printBuff(ByteBuffer sbf, ByteBuffer rbf);

    public static void main(String[] args) {
        ByteBuffer bf = ByteBuffer.allocateDirect(10);
        ByteBuffer rbf = ByteBuffer.allocateDirect(10);
        byte bbs[] = "abc".getBytes();
        bf.put(bbs);
        System.out.println("Before swap " + (char) (rbf).get());
        (new ByteBuff()).printBuff(bf, rbf);
        System.out.println("Before swap " + (char) (rbf).get());
    }
}

ByteBuff.c

#include "ByteBuff.h"
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

JNIEXPORT void JNICALL Java_ByteBuff_printBuff (JNIEnv *env, jobject jobj, jobject sbuf,jobject rbuf) {
    jbyte* sbufp=(*env)->GetDirectBufferAddress(env,sbuf);
    jbyte* rbufp=(*env)->GetDirectBufferAddress(env,rbuf);

    MPI_Request sreq,rreq;
    MPI_Status sstatus,rstatus;
    MPI_Init(NULL,NULL);
    MPI_Isend(sbufp,3,MPI_BYTE,0,0,MPI_COMM_WORLD,&sreq);
    MPI_Recv(rbufp,3,MPI_BYTE,0,0,MPI_COMM_WORLD,&rstatus);
    MPI_Wait(&sreq,&sstatus);
    MPI_Finalize();

    (*env)->ReleasePrimitiveArrayCritical(env,sbuf,sbufp,0);
    (*env)->ReleasePrimitiveArrayCritical(env,rbuf,rbufp,0);
}

编译动态库的时候需要链接MPI的静态库（本文使用MVAPICH 1.8.x），编译命令为

gcc -std=c99 -shared -fPIC -I /usr/local/mvapich/include/ -I /usr/local/jdk1.6.0_30/include/ -I /usr/local/jdk1.6.0_30/include/linux/ -I /usr/local/ ByteBuff.c -o libbuff.so  -lpthread /usr/local/mvapich/lib/libmpich.a /usr/local/mvapich/lib/libopa.a /usr/local/mvapich/lib/libmpl.a -lrt -lpthread /usr/local/mvapich/lib/libmpich.a /usr/local/mvapich/lib/libopa.a /usr/local/mvapich/lib/libmpl.a -lrt

执行结果

$ mpiexec -n 1 java -Djava.library.path=. ByteBuff
Before swap 
Before swap b