import mpi.*
public class Sum {
public static void main(String[] args) throws Exception {
String[] userArgs = MPI.Init(args);
int sum =0;
int [] partial_sum = new int [1];
int n;
int[] array = new int[100];
int[] array2 = new int[100];
int i;
int num_rows = 0;
int num_procs;
int an_id;
int num_rows_to_receive = 0;
int avg_rows_per_process = 0;
int num_rows_received;
int start_row;
int end_row;
int num_rows_to_send;
/* Now replicte this process to create parallel processes.
* From this point on, every process executes a seperate copy
* of this program */
/* find out MY process ID, and how many processes were started. */
int myrank = MPI.COMM_WORLD.Rank();
int size = MPI.COMM_WORLD.Size();
int input_size = Integer.parseInt(userArgs[0]);
if(myrank == 0) {
avg_rows_per_process = input_size / size;
n = input_size;
/* initialize an array */
for(i = 0; i < n; i++){
array[i] = i + 1;
}
System.out.println(n);
/* distribute a portion of the vector to each child process */
for(an_id = 1; an_id < size; an_id++) {
start_row = an_id*avg_rows_per_process + 1;
end_row = (an_id + 1)*avg_rows_per_process;
if((num_rows - end_row) < avg_rows_per_process) end_row = num_rows - 1;
num_rows_to_send = end_row - start_row + 1;
MPI.COMM_WORLD.Send(array, start_row, num_rows_to_send, MPI.INT, an_id, 0);
}
MPI.COMM_WORLD.Barrier();
/* and calculate the sum of the values in the segment assigned
* to the root process */
sum = 0;
for(i = 0; i < avg_rows_per_process + 1; i++) {
sum += array[i];
}
System.out.println("Sum calculated by root process" + sum);
MPI.COMM_WORLD.Barrier();
/* and, finally, I collect the partial sums from the slave processes,
* print them, and add them to the grand sum, and print it */
for(an_id = 1; an_id < size; an_id++){
MPI.COMM_WORLD.Recv(partial_sum, 0, 1, MPI.INT, 0, 0);
System.out.println("Partial sum " + partial_sum[0] + " returned from process " + an_id);
sum += partial_sum[0];
}
System.out.println("The grand total is: " + sum);
}
MPI.COMM_WORLD.Barrier();
/* I must be a slave process, so I must receive my array segment,
* storing it in a "local" array, array1. */
if (myrank!=0){
array2[0] =0;
MPI.COMM_WORLD.Recv(array2, 0, num_rows_to_receive, MPI.INT, 0, 1);
num_rows_received = num_rows_to_receive;
/* Calculate the sum of my portion of the array */
partial_sum[0] = 0;
for(i = 0; i < num_rows_received; i++) {
partial_sum[0] += array2[i];
}
System.out.println("partial sum from process " + myrank + " is " + partial_sum[0]);
/* and finally, send my partial sum to the root process */
MPI.COMM_WORLD.Send(partial_sum, 0 ,1 , MPI.INT, 0, 1);
}
MPI.Finalize();
}
}
I wrote this java code summing an array using MPI. I am new to this. I am little bit confused with where to give my barriers. and this code is with many errors. please give me some advice on this.
here is the error log:
MPJ Express (0.38) is started in the multicore configuration
5
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at runtime.starter.MulticoreStarter$1.run(MulticoreStarter.java:289)
at java.lang.Thread.run(Unknown Source)
Caused by: mpi.MPIException: java.lang.NullPointerException
at mpi.BasicType.createWriteBuffer(BasicType.java:192)
at mpi.Comm.send(Comm.java:362)
at mpi.Comm.Send(Comm.java:332)
at Sum.main(Sum.java:67)
... 6 more
Caused by: java.lang.NullPointerException
at mpjbuf.Buffer.putSectionHeader(Buffer.java:628)
at mpi.BasicType.createWriteBuffer(BasicType.java:189)
... 9 more
thanks!
