MPI_Irecv没有收到全部发送？

Question

我试图在这个简化的代码acheive是：（分别为根，和儿童，IDS /秩= 10和0-9）

• 2类型的过程
• INIT：
  • 根会听“已完成”
  • 孩子会听根通知儿童在所有已完成
• 虽然没有赢家（不是全部没有完成）： 点
  • 的孩子将有20％的机会，他们将完成（并通知根他们这样做）
  • 根将检查全部弄完
    • 如果全部完成：发送通知的“胜利者”孩子

我有这样的代码：

int numprocs, id, arr[10], winner = -1; 
bool stop = false; 
MPI_Request reqs[10], winnerNotification; 

MPI_Init(NULL, NULL); 
MPI_Comm_size(MPI_COMM_WORLD, &numprocs); 
MPI_Comm_rank(MPI_COMM_WORLD, &id); 

for (int half = 0; half < 1; half++) { 
    for (int round = 0; round < 1; round++) { 
     if (id == 10) { // root 
      // keeps track of who has "completed" 
      fill_n(arr, 10, -1); 
      for (int i = 0; i < 10; i++) { 
       MPI_Irecv(&arr[i], 1, MPI_INT, i, 0, MPI_COMM_WORLD, &reqs[i]); 
      } 
     } else if (id < 10) { // children 
      // listen to root of winner notification/indication to stop 
      MPI_Irecv(&winner, 1, MPI_INT, 10, 1, MPI_COMM_WORLD, &winnerNotification); 
     } 

     while (winner == -1) { 
      //cout << id << " is in loop" << endl; 

      if (id < 10 && !stop && ((rand() % 10) + 1) < 3) { 
       // children has 20% chance to stop (finish work) 
       MPI_Send(&id, 1, MPI_INT, 10, 0, MPI_COMM_WORLD); 
       cout << id << " sending to root" << endl; 
       stop = true; 
      } else if (id == 10) { 
       // root checks number of children completed 
       int numDone = 0; 
       for (int i = 0; i < 10; i++) { 
        if (arr[i] >= 0) { 
         //cout << "root knows that " << i << " has completed" << endl; 
         numDone++; 
        } 
       } 
       cout << "numDone = " << numDone << endl; 

       // if all done, send notification to players to stop 
       if (numDone == 10) { 
        winner = 1; 
        for (int i = 0; i < 10; i++) { 
         MPI_Send(&winner, 1, MPI_INT, i, 1, MPI_COMM_WORLD); 
        } 
        cout << "root sent notification of winner" << endl; 
       } 
      } 
     } 
    } 
} 

MPI_Finalize(); 

调试输出cout看起来像：问题似乎是根并没有收到他们完成的所有儿童通知？

2 sending to root 
3 sending to root 
0 sending to root 
4 sending to root 
1 sending to root 
8 sending to root 
9 sending to root 
numDone = 1 
numDone = 1 
... // many numDone = 1, but why 1 only? 
7 sending to root 
... 

我想也许我不能接收到一个数组：但我想

if (id == 1) { 
    int x = 60; 
    MPI_Send(&x, 1, MPI_INT, 0, 0, MPI_COMM_WORLD); 
} else if (id == 0) { 
    MPI_Recv(&arr[1], 1, MPI_INT, 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE); 
    cout << id << " recieved " << arr[1] << endl; 
} 

其中一期工程。

UPDATE

这似乎可以解决，如果我在while循环结束前添加MPI_Barrier(MPI_COMM_WORLD)，但是为什么呢？即使这些进程不同步，最终，孩子们会发送到root，他们已经完成，root应该“听”并相应地进行处理？似乎在发生的事情是，root一直在运行，占用了所有资源供儿童执行？或者这里发生了什么？

更新2：有些孩子不从根本得到通知

好了，现在根本没有收到，他们已经通过@ MichaelSh的回答完成儿童通知的问题，我专注于儿童无法从父母接受。下面是重现该问题的代码：

int numprocs, id, arr[10], winner = -1; 
bool stop = false; 
MPI_Request reqs[10], winnerNotification; 

MPI_Init(NULL, NULL); 
MPI_Comm_size(MPI_COMM_WORLD, &numprocs); 
MPI_Comm_rank(MPI_COMM_WORLD, &id); 

srand(time(NULL) + id); 

if (id < 10) { 
    MPI_Irecv(&winner, 1, MPI_INT, 10, 0, MPI_COMM_WORLD, &winnerNotification); 
} 
MPI_Barrier(MPI_COMM_WORLD); 

while (winner == -1) { 
    cout << id << " is in loop ..." << endl; 
    if (id == 10) { 
     if (((rand() % 10) + 1) < 2) { 
      winner = 2; 
      for (int i = 0; i < 10; i++) { 
       MPI_Send(&winner, 1, MPI_INT, i, 0, MPI_COMM_WORLD); 
      } 
      cout << "winner notifications sent" << endl; 
     } 
    } 
} 

cout << id << " b4 MPI_Finalize. winner is " << winner << endl; 

MPI_Finalize(); 

输出的样子：

# 1 run 
winner notifications sent 
10 b4 MPI_Finalize. winner is 2 
9 b4 MPI_Finalize. winner is 2 
0 b4 MPI_Finalize. winner is 2 

# another run 
winner notifications sent 
10 b4 MPI_Finalize. winner is 2 
8 b4 MPI_Finalize. winner is 2 

注意某些进程似乎没有得到家长的通知？为什么呢，子进程的MPI_Wait只会挂住它们？那么我该如何解决这个问题？

而且

所有MPI_Barrier做你的情况 - 它等待孩子的反应来完成。请检查我的答案以获得更好的解决方案

如果我不这样做，我想每个孩子的回答只需几毫秒？所以，即使我不等待/屏障，我希望收到发送后不久仍然会发生？除非流程最终会占用资源，其他流程不会运行？

Answer 1

请尝试以下代码块（检查省略了简单的错误）：

... 
// root checks number of children completed 
int numDone = 0; 
MPI_Status statuses[10]; 
MPI_Waitall(10, reqs, statuses); 
for (int i = 0; i < 10; i++) { 
... 

编辑更好的解决方案：
每个孩子发起根赢家通知接收和发送其通知到根。
Root向阵列启动优胜者通知收据并进入等待接收的所有通知，然后将优胜者的ID发送给儿童。 插入下面这段代码后for (int round = 0; round < 1; round++)

  if (id == 10) 
      { // root 
       // keeps track of who has "completed" 
       memset(arr, -1, sizeof(arr)); 
       for (int i = 0; i < 10; i++) 
       { 
        MPI_Irecv(&arr[i], 1, MPI_INT, i, 0, MPI_COMM_WORLD, &reqs[i]); 
       } 
      } 
      else if (id < 10) 
      { // children 
       // listen to root of winner notification/indication to stop 
       MPI_Irecv(&winner, 1, MPI_INT, 10, 1, MPI_COMM_WORLD, &winnerNotification); 
      } 

      if (id < 10) 
      { 
       while(((rand() % 10) + 1) < 3) ; 

       // children has 20% chance to stop (finish work) 
       MPI_Send(&id, 1, MPI_INT, 10, 0, MPI_COMM_WORLD); 
       std::cout << id << " sending to root" << std::endl; 
       // receive winner notification 
       MPI_Status status; 
       MPI_Wait(&winnerNotification, &status); 
       // Process winner notification 
      } 
      else if (id == 10) 
      { 
       MPI_Status statuses[10]; 
       MPI_Waitall(10, reqs, statuses);      

       // if all done, send notification to players to stop 
       { 
        winner = 1; 
        for (int i = 0; i < 10; i++) 
        { 
         MPI_Send(&winner, 1, MPI_INT, i, 1, MPI_COMM_WORLD); 
        } 
        std::cout << "root sent notification of winner" << std::endl; 
       } 
      }