MPI_Barrier不是循環

Question

我已經運行的MPI函數的一些測試，以瞭解它是如何工作的，並得到了與MPI_Barrier怪異的結果裏面工作：它如果我使用它的代碼就像

int main(int argc, char *argv[]) 
{ 
    <some code> 
    MPI_Barrier(MPI_COMM_WORLD); 
    <more code> 
    MPI_Barrier(MPI_COMM_WORLD); 
    <...> 
} 

大家所期待的

但是當我從循環內部調用它時，我得到了隨機結果。具體而言，我有以下的測試代碼：

#include "mpi.h" 
#include <stdio.h> 

int main(int argc, char *argv[]) 
{ 
    int i, rb, rank, nprocs; 

    MPI_Init(&argc,&argv); 
    MPI_Comm_size(MPI_COMM_WORLD,&nprocs); 
    MPI_Comm_rank(MPI_COMM_WORLD,&rank); 

    i=0; 
    while(i<5) 
    { 
    rb=MPI_Barrier(MPI_COMM_WORLD); 
    printf("Itartion %d. I am %d of %d. MPIBarrierRes: %d\n", i, rank, nprocs, rb); 
    i++; 
    } 
    MPI_Finalize(); 
    return 0; 
} 

當我與3個任務運行它，我隨機得到：

Itartion 0. I am 0 of 3. MPIBarrierRes: 0 
Itartion 0. I am 2 of 3. MPIBarrierRes: 0 
Itartion 0. I am 1 of 3. MPIBarrierRes: 0 
Itartion 1. I am 0 of 3. MPIBarrierRes: 0 
Itartion 1. I am 1 of 3. MPIBarrierRes: 0 
Itartion 1. I am 2 of 3. MPIBarrierRes: 0 
Itartion 2. I am 0 of 3. MPIBarrierRes: 0 
Itartion 2. I am 1 of 3. MPIBarrierRes: 0 
Itartion 2. I am 2 of 3. MPIBarrierRes: 0 
Itartion 3. I am 0 of 3. MPIBarrierRes: 0 
Itartion 3. I am 1 of 3. MPIBarrierRes: 0 
Itartion 3. I am 2 of 3. MPIBarrierRes: 0 
Itartion 4. I am 0 of 3. MPIBarrierRes: 0 
Itartion 4. I am 1 of 3. MPIBarrierRes: 0 
Itartion 4. I am 2 of 3. MPIBarrierRes: 0 

這是啥子我應該想到，或者只是oposite：

Itartion 0. I am 2 of 3. MPIBarrierRes: 0 
Itartion 1. I am 2 of 3. MPIBarrierRes: 0 
Itartion 2. I am 2 of 3. MPIBarrierRes: 0 
Itartion 3. I am 2 of 3. MPIBarrierRes: 0 
Itartion 4. I am 2 of 3. MPIBarrierRes: 0 
Itartion 0. I am 0 of 3. MPIBarrierRes: 0 
Itartion 1. I am 0 of 3. MPIBarrierRes: 0 
Itartion 2. I am 0 of 3. MPIBarrierRes: 0 
Itartion 3. I am 0 of 3. MPIBarrierRes: 0 
Itartion 4. I am 0 of 3. MPIBarrierRes: 0 
Itartion 0. I am 1 of 3. MPIBarrierRes: 0 
Itartion 1. I am 1 of 3. MPIBarrierRes: 0 
Itartion 2. I am 1 of 3. MPIBarrierRes: 0 
Itartion 3. I am 1 of 3. MPIBarrierRes: 0 
Itartion 4. I am 1 of 3. MPIBarrierRes: 0 

或介於兩者之間，像

Itartion 0. I am 1 of 3. MPIBarrierRes: 0 
Itartion 0. I am 0 of 3. MPIBarrierRes: 0 
Itartion 1. I am 0 of 3. MPIBarrierRes: 0 
Itartion 0. I am 2 of 3. MPIBarrierRes: 0 
Itartion 1. I am 1 of 3. MPIBarrierRes: 0 
Itartion 2. I am 0 of 3. MPIBarrierRes: 0 
Itartion 1. I am 2 of 3. MPIBarrierRes: 0 
Itartion 2. I am 1 of 3. MPIBarrierRes: 0 
Itartion 3. I am 0 of 3. MPIBarrierRes: 0 
Itartion 2. I am 2 of 3. MPIBarrierRes: 0 
Itartion 3. I am 1 of 3. MPIBarrierRes: 0 
Itartion 4. I am 0 of 3. MPIBarrierRes: 0 
Itartion 3. I am 2 of 3. MPIBarrierRes: 0 
Itartion 4. I am 1 of 3. MPIBarrierRes: 0 
Itartion 4. I am 2 of 3. MPIBarrierRes: 0 

任何人都可以告訴我，如果MPI_Barrier和循環之間有一些衝突嗎？ （我只發現了警告，以避免在不同任務中使用不同大小的循環造成死鎖。） 如果有一個，我可以如何強制任務在開始循環的新迭代之前等待對方？ 如果沒有，這個代碼有什麼問題？

謝謝！

Answer 1

它與你的循環無關。 MPI沒有暗示IO的序列化。如果您需要打印出來，您必須明確地將它們發送到一個等級，並在那裏打印出來。