MPI流程同步 [英] MPI process synchronization

问题描述

我仍然对使用MPI实施程序感到困惑.这是我的示例:

I'm still confused about the implementation of my program using MPI. This is my example:

 import mpi.*;
 public class HelloWorld {
     static int me;
     static Object [] o = new Object[1];
     public static void main(String args[]) throws Exception {
       //10 processes were started: -np 10
       MPI.Init(args);
       me = MPI.COMM_WORLD.Rank();
       if(me == 0) {
            o[0] = generateRandBoolean(0.5);
            for(int i=1; i<10;i++) 
                MPI.COMM_WORLD.Isend(o, 0, 1, MPI.OBJECT, i,0);
            if((Boolean)o[0])
                MPI.COMM_WORLD.Barrier();
        } else {

            (new HelloWorld()).work();
        }
        MPI.Finalize();
    }

    public void work() {
        //do some calculation
            //for some reason, the 10th process
        //will not be needed
            if(me == 9) 
            return;

        //some times, the rest of the
        //processes have to be synchronized
        Request rreq = MPI.COMM_WORLD.Irecv(o, 0, 1, MPI.OBJECT, MPI.ANY_SOURCE, 0);
        rreq.Wait();
        if((Boolean)o[0])
            MPI.COMM_WORLD.Barrier();
    }

    public static boolean generateRandBoolean(double p) {
        return (Math.random() < p);
    }
}

问题是，在某些情况下，我不需要所有进程，所以我不知道该如何处理空闲的进程.首先，我返回了不需要的进程，但是如果其余进程需要与Barrier()进行同步，则会产生问题.

The problem is that in some cases, I will not need all the processes, so I don't know what to do with the idle ones. At first, I was returning the not needed processes, but it generates problem if the rest of the processes need to be synchronized with Barrier().

我以为我可以让不需要运行的进程等待消息完成或致电屏障，但这对我来说听起来并不好.

I thought I could let the processes I don't need running waiting for a message to finish or to call Barrier, but it does not sound good to me.

此外，我读到呼叫Barrier会降低性能，所以我宁愿不使用它.

Also, I read that calling Barrier has a performance penalty, so I would prefer not to use it.

如何实现所需的同步?

非常感谢您.

推荐答案

使用MPI_Barrier收集程序末尾的所有等级.

Use MPI_Barrier to collect all the ranks at the end of the program.

在MPI的所有合理实现中，如果还有其他工作要做，则集合中的等级将旋转或产生处理器.这看起来很像是等级消耗了100％的CPU ...但是，如果实际上有任何其他工作要做，它将被调度并允许运行.

In all reasonable implementations of MPI, the ranks in a collective will spin or yield the processor if there are any other processes that have work to do. This may look a lot like the rank is consuming 100% of the CPU...but if any other process actually has work to do it will be scheduled and allowed to run.

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