MPJ Express发送和接收-ClassCastException

Question

我看过这个，但它并没有真正帮助，因为我处理的是基元，而不是对象。这只是一个额外部分的一部分。虽然它很好，但我想让它发挥作用。

它的编译很好，但当我运行它时，我在第20行得到一个ClassCastException。

/* Java Version (mine) */    
public class PingPongJava { 
    public static void main(String args[]) throws Exception { 
        int me;
        int size;
        int recv_buf = 0;
        int buf = 0;
        int send_buf = 101;
        double tic = 0, toc = 0;
        MPI.Init(args);
        me = MPI.COMM_WORLD.Rank();
        size = MPI.COMM_WORLD.Size();
        tic = MPI.Wtime();
        for (int i = 0; i < 50; i++){
            if (me == 0){
            MPI.COMM_WORLD.Send(send_buf, 0,1,MPI.INT, 17, 100);
            MPI.COMM_WORLD.Recv(recv_buf, 0,1, MPI.INT, 23, 100);
            }
            else{
            MPI.COMM_WORLD.Recv(buf, 0, 1, MPI.INT, 17, 100);
            MPI.COMM_WORLD.Send(buf, 0,1,MPI.INT, 23, 100);
            }
        }
        toc = MPI.Wtime();
        if (me == 0){
            System.out.println("Time taken is " + (toc-tic)/100);
            }
        MPI.Finalize(); 
     }
    } 

我正在从这个C版本转换

/* Point-to-point communication.
 */
#include <mpi.h>
#include <stdio.h>
int main(int argc, char **argv){
  int rank, size, i, recv_buf, send_buf=101, buf;
  MPI_Status status;
  double tic, toc;
  MPI_Init(&argc, &argv);
  MPI_Comm_rank (MPI_COMM_WORLD, &rank);
  MPI_Comm_size (MPI_COMM_WORLD, &size);
  tic = MPI_Wtime();
  for(i=0;i<50;i++){
    if(rank==0){
      MPI_Send(&send_buf, 1, MPI_INT, 1, 17 , MPI_COMM_WORLD);
      MPI_Recv(&recv_buf, 1, MPI_INT, 1, 23, MPI_COMM_WORLD, &status);
    }else{
      MPI_Recv(&buf, 1, MPI_INT, 0, 17, MPI_COMM_WORLD, &status);
      MPI_Send(&buf, 1, MPI_INT, 0, 23, MPI_COMM_WORLD);
    }
  }
  toc = MPI_Wtime();
  if(rank==0)
    printf("Average time for a single message: %lf seconds n", (toc-tic)/100.0);
  MPI_Finalize();
  return 0;
}

Answer 1

首先，必须对变量recv_buf、buf、send_buf使用数组类型。其次，您在发送、接收签名中的最后两个参数是错误的。它们必须是：发送中的"..destination，tag）"和接收中的"..source，tag））"。我在下面的代码中纠正了你的错误。

public class PingPongJava {
    public static void main(String args[]) throws Exception {
        int me;
        int size;
        int[] recv_buf = { 0 };
        int[] buf = {0};
        int[] send_buf = { 101 };
        double tic = 0, toc = 0;
        MPI.Init(args);
        me = MPI.COMM_WORLD.Rank();
        size = MPI.COMM_WORLD.Size();
        tic = MPI.Wtime();
        for (int i = 0; i < 50; i++) {
            if (me == 0) {
                MPI.COMM_WORLD.Send(send_buf, 0, 1, MPI.INT, 1, 17);
                MPI.COMM_WORLD.Recv(recv_buf, 0, 1, MPI.INT, 1, 23);
            } else {
                MPI.COMM_WORLD.Recv(buf, 0, 1, MPI.INT, 0, 17);
                MPI.COMM_WORLD.Send(buf, 0, 1, MPI.INT, 0, 23);
            }
        }
        toc = MPI.Wtime();
        if (me == 0) {
            System.out.println("Time taken is " + (toc - tic) / 100);
        }
        MPI.Finalize();
    }
}