MPI_Irecv不接收所有发送

我试图在这个简化的代码中实现的是：

• 两种类型的进程(根进程和子进程，ids/rank=10和0-9)
• 初始化：
  • root将听孩子们"完成">
  • 所有操作完成后，子级将侦听根通知
• 虽然没有赢家(还没有全部完成)：
  • 孩子们将有20%的机会完成任务(并通知root他们完成了任务)
  • root将检查是否已完成所有操作
    • 如果全部完成：向"获胜者"的孩子发送通知

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cout的输出看起来像：问题似乎是root没有收到所有子级的完成通知？

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
...

我想也许我无法接收到数组：但我尝试了

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;
}

这是有效的。

更新

如果我在while循环结束之前添加一个MPI_Barrier(MPI_COMM_WORLD)，这似乎可以解决，但为什么呢？即使进程不同步，最终，孩子们也会向root发送他们已经完成的信息，root应该"倾听"并进行相应的处理？似乎正在发生的是root一直在运行，占用了孩子们执行的所有资源？或者这里发生了什么？

更新2：一些孩子没有收到来自root的通知

好吧，现在root没有收到孩子们通过@MichaelSh的回答完成的通知的问题，我关注的是孩子们没有收到家长的通知。这里有一个代码再现了这个问题：

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();

输出看起来像：

# 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

注意到有些进程似乎没有从父进程获得通知吗？为什么子进程的MPI_Wait会挂起它们？那么我该如何解决这个问题呢？

还有

在您的案例中，所有MPI_Barrier都会这样做——它会等待子响应完成。请检查我的答案以获得更好的解决方案

如果我不这样做，我想每个孩子的响应只需要几毫秒？所以，即使我不等待/设置障碍，我也希望在发送后不久仍能收到？除非进程最终占用资源，而其他进程不运行？