Java OpenMPI 安裝

1. 下載jdk8:http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

2. 解壓jdk:

   tar -zxvf /Dowloads/jdk-8u161-linux-x64.tar.gz

3. 下載openMPI：https://www.open-mpi.org/software/ompi/v3.0/

4. 解壓OpenMPI：

   tar -zxvf /Dowloads/openmpi-3.0.0.tar.gz

5. 配置包含Java的Makefile，編譯：

   ./configure --prefix=/opt/openmpi --enable-mpi-java ##不加prefix可能找不到mpi.jar
   
   make
   
   sudo make install

6. 配置環境變量（如 .bashrc）

   export JAVA_HOME=/root/Downloads/jdk1.8.0_161
   export JRE_HOME=${JAVA_HOME}/jre
   export MPI_HOME=/opt/openmpi
   export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib:${MPI_HOME}/lib
   export PATH=${JAVA_HOME}/bin:${MPI_HOME}/bin:$PATH

7. 檢查是否正常運行

   import mpi.*;
   
   class ComputePi {
   
      public static void main(String args[]) throws MPIException {
   
          MPI.Init(args);
   
          int rank = MPI.COMM_WORLD.getRank(),
              size = MPI.COMM_WORLD.getSize(),
              nint = 100; // Intervals.
          double h = 1.0/(double)nint, sum = 0.0;
   
          for(int i=rank+1; i<=nint; i+=size) {
              double x = h * ((double)i - 0.5);
              sum += (4.0 / (1.0 + x * x));
          }
   
          double sBuf[] = { h * sum },
                 rBuf[] = new double[1];
   
          MPI.COMM_WORLD.reduce(sBuf, rBuf, 1, MPI.DOUBLE, MPI.SUM, 0);
   
          if(rank == 0) System.out.println("PI: " + rBuf[0]);
          MPI.Finalize();
      }
   }

8. 在當前路徑下建立hosts文件（單機）

   localhost    slots=4 ##表示使用本機的4個進程

9. 編譯並運行代碼

   mpijavac ComputePi.java
   mpiexec --hostfile hosts -np 4 --allow-run-as-root java ComputePi
   mpirun --allow-run-as-root lr

10. 顯示結果：

    PI: 3.141600986923125

    ​