c - MPI 环领导选举返回分段错误

Question

这就是我想要达到的目标。

Blue is the message.
Yellow is when the specific node changes the leader known to it.
Green is the final election of each node.

该代码对我来说似乎是正确的，但无论我尝试什么，它总是卡在 while 循环中。对于运行时的少数节点，它会在一段时间后返回分段错误。

election_status=0;
firstmsg[0]=world_rank;     // self rank
firstmsg[1]=0;              // counter for hops
chief=world_rank;           // each node declares himself as leader
counter=0;                  // message counter for each node

// each node sends the first message to the next one
MPI_Send(&firstmsg, 2, MPI_INT, (world_rank+1)%world_size, 1, MPI_COMM_WORLD);
printf("Sent ID with counter to the right node [%d -> %d]\n",world_rank, (world_rank+1)%world_size);

while (election_status==0){
    // EDIT: Split MPI_Recv for rank 0 and rest
    if (world_rank==0){
        MPI_Recv(&incoming, 2, MPI_INT, world_size-1, 1, MPI_COMM_WORLD, &status);
    }
    else {
        MPI_Recv(&incoming, 2, MPI_INT, (world_rank-1)%world_size, 1, MPI_COMM_WORLD, &status);
    }
    counter=counter+1;
    if (incoming[0]<chief){
        chief=incoming[0];
    }
    incoming[1]=incoming[1]+1;

    // if message is my own and hopped same times as counter
    if (incoming[0]==world_rank && incoming[1]==counter) {
        printf("Node %d declares node %d a leader.\n", world_rank, chief);  
        election_status=1;
    }
    //sends the incremented message to the next node
    MPI_Send(&incoming, 2, MPI_INT, (world_rank+1)%world_size, 1, MPI_COMM_WORLD);  
}

MPI_Finalize();

Answer 1

为了确定所有等级的多个等级中的某个最小数量，请使用MPI_Allreduce!

• MPI_Send正在阻塞。它可以永远阻塞，直到发布匹配的接收。您的程序在第一次调用 MPI_Send 时出现死锁 - 任何后续的一次调用都应该巧合完成。为了避免这种情况，专门使用MPI_Sendrecv.
• (world_rank-1)%world_size将产生-1. world_rank == 0用作-1排名编号无效。可能是巧合MPI_ANY_SOURCE。