用MPI-C语言编写程序

我的MPI C程序有问题。代码如下：

void wantEat(int p, int rank, char *state, char* stateLeft, char* stateRight){

    char *s;

    MPI_Status status ;

    /* if left or right neighbor is eating */

    if(compare(stateLeft, "eat") || compare (stateRight, "eat")){
        state = "want_Eat";
        printf("%s : I wait for eating\n", nomPhilosophe(rank));

        /* the process have to send his new state to his neighbors */

        MPI_Send(state, strlen(state)+1, MPI_CHAR,
                (rank - 1 + p) % p, 0, MPI_COMM_WORLD);
        MPI_Send(state, strlen(state)+1, MPI_CHAR,
                (rank + 1) % p, 0, MPI_COMM_WORLD);

        /* if only left neighbor is eating */

        if(compare(stateLeft,"eat") &&  !compare(stateRight,"eat")){

            /* Wait for left neighbor finishes eating */

            MPI_Recv(stateLeft, 6, MPI_CHAR, (rank - 1 + p) % p, 0,
                    MPI_COMM_WORLD, &status);
            /* and eat */
            state = "eat";
        }
        /* if only right neighbor is eating  */

        if(compare(stateRight,"eat") &&  !compare(stateLeft,"eat")){

            /* wait for right neighbor message */
            MPI_Recv(stateRight, 6, MPI_CHAR, (rank + 1) % p, 0,
                    MPI_COMM_WORLD, &status);
            /* and eat */
            state = "eat";
        }
        /* if both neighboors are eating */

        if(compare(stateRight,"eat") &&  compare(stateLeft,"eat")){

            /* wait for messages of the 2 neighbors */

            MPI_Recv(stateLeft, strlen("think")+1, MPI_CHAR, MPI_ANY_SOURCE, 0,
                    MPI_COMM_WORLD, &status);
            MPI_Recv(stateRight, strlen("think")+1, MPI_CHAR, MPI_ANY_SOURCE, 0,
                    MPI_COMM_WORLD, &status);

            /* and eat */
            state = "eat";
        }
    }

    /* if neighbors are not eating */

    else{
        /* eat */ 
        state= "eat";
    }

    /* send the new state to neighbors */

    MPI_Send(state, strlen(state)+1, MPI_CHAR,
            (rank - 1 + p) % p, 0, MPI_COMM_WORLD);
    MPI_Send(state, strlen(state)+1, MPI_CHAR,
            (rank + 1) % p, 0, MPI_COMM_WORLD);
}

int main(int argc, char* argv[]){
    int  my_rank; /* rank of process */
    int  p;       /* number of processes */

    char* state = "think";   /* state of process (think, eat, or want_eat) */
    char* stateLeft = "think";  /* state of the left neighbor of the      process  */
    char* etatD = "think";  /* state of the right neighbor of the process */

    /* start up MPI */

    MPI_Init(&argc, &argv);

    /* find out process rank */
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank); 

    /* find out number of processes */
    MPI_Comm_size(MPI_COMM_WORLD, &p); 

    think(my_rank); /* process "my_rank" is thinking */
    wantEat(p, my_rank, state, stateLeft, stateRight); /* process "my_rank" wants to eat */
    eat(my_rank); /* process "my_rank" is eating */ 



    /* shut down MPI */
    MPI_Finalize(); 


    return 0;
}

---

问题是，所有进程都在不等待邻居的情况下同时进食。我认为新州的MPI发送不会被邻居接收到。你有办法解决这个问题吗？

你的程序启动了，每个人都处于状态

“思考”

。这意味着在所有进程中都会跳过if语句，因为没有人在吃东西，每个人都执行else语句并将其状态设置为“eat”。然后，他们每次调用

MPI\u Send

，等待邻居调用

MPI\u Recv

，但他们不能，因为他们也被困在

MPI\u Send

上，所以我想你的程序会挂起吗？我是不是在你没有展示的功能中遗漏了一些特别的东西？为什么您希望行为与此不同？在我的“思考”函数中，每个进程都会等待一段随机时间，然后才会想吃东西，因此进程不希望在完全相同的时间吃东西。我想我应该为我的每个MPI_发送添加一个MPI_recv，但我不知道在哪里。事实上，每个进程在

recv

it之前都不知道关于其邻居状态的任何其他信息。最好在

wantEat

函数的开头执行

MPI\u Sendrecv

，以便每个进程都知道其邻居的最新信息，然后相应地更改其状态

Sendrecv

还可以帮助解决您可能遇到的悬而未决的问题，因为您不必担心在不同进程上发送和接收的顺序。