MPI中通信器之间的发送和接收操作 [英] Send and Receive operations between communicators in MPI

问题描述

我之前的问题:无法实现MPI_Intercomm_create

MPI_INTERCOMM_CREATE的问题已解决.但是，当我尝试在颜色0的进程0(全局等级= 0)和颜色1的进程0(即全局等级= 2)之间实现基本的发送接收操作时，代码只是在打印接收到的缓冲区后挂断. 代码:

The problem of MPI_INTERCOMM_CREATE has been solved. But when I try to implement a basic send receive operations between process 0 of color 0 (globally rank = 0) and process 0 of color 1 (ie globally rank = 2), the code just hangs up after printing received buffer. the code:

program hello
include 'mpif.h'
implicit none 
integer tag,ierr,rank,numtasks,color,new_comm,inter1,inter2
integer sendbuf,recvbuf,tag,stat(MPI_STATUS_SIZE)

tag = 22
sendbuf = 222

call MPI_Init(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD,rank,ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD,numtasks,ierr)

if (rank < 2) then
color = 0
else 
color = 1
end if

call MPI_COMM_SPLIT(MPI_COMM_WORLD,color,rank,new_comm,ierr)

if (color .eq. 0) then
if (rank == 0) print*,' 0 here'
call MPI_INTERCOMM_CREATE(new_comm,0,MPI_Comm_world,2,tag,inter1,ierr)
call mpi_send(sendbuf,1,MPI_INT,2,tag,inter1,ierr)

!local_comm,local leader,peer_comm,remote leader,tag,new,ierr

else if(color .eq. 1) then
 if(rank ==2) print*,' 2 here'
call MPI_INTERCOMM_CREATE(new_comm,2,MPI_COMM_WORLD,0,tag,inter2,ierr)
call mpi_recv(recvbuf,1,MPI_INT,0,tag,inter2,stat,ierr)
print*,recvbuf
end if
end

推荐答案

大多数用户对互通通信并不十分了解，示例不如其他MPI操作示例那么多.您可以按照此链接.

The communication with intercommunication is not well understood by most users, and examples are not as many as examples for other MPI operations. You can find a good explanation by following this link.

现在，有两件事要记住:

Now, there are two things to remember:

1)内部通信器中的通信总是从一个组转移到另一组.发送时，目的地的等级是其在远程组通信器中的本地等级.接收时，发件人的等级是其在远程组通信器中的本地等级.

1) Communication in an inter communicator always go from one group to the other group. When sending, the rank of the destination is its the local rank in the remote group communicator. When receiving, the rank of the sender is its local rank in the remote group communicator.

2)点对点通信(MPI_send和MPI_recv系列)位于一个发送方和一个接收方之间.在您的情况下，颜色为0的每个人都在发送，颜色为1的每个人都在接收，但是，如果我理解您的问题，则您希望颜色0的进程0将某些内容发送给进程的颜色为1.

2) Point to point communication (MPI_send and MPI_recv family) is between one sender and one receiver. In your case, everyone in color 0 is sending and everyone in color 1 is receiving, however, if I understood your problem, you want the process 0 of color 0 to send something to the process 0 of color 1.

发送代码应如下所示:

call MPI_COMM_RANK(inter1,irank,ierr)
if(irank==0)then
    call mpi_send(sendbuf,1,MPI_INT,0,tag,inter1,ierr)
end if

接收代码应类似于:

call MPI_COMM_RANK(inter2,irank,ierr)
if(irank==0)then
    call mpi_recv(recvbuf,1,MPI_INT,0,tag,inter2,stat,ierr)
    print*,'rec buff = ', recvbuf
end if

在示例代码中，有一个新变量irank，我用它来查询内部通信器中每个进程的等级.那是他当地沟通者的过程等级.因此，您将有两个等级为0的过程，每个组一个，依此类推.

In the sample code, there is a new variable irank that I use to query the rank of each process in the inter-communicator; that is the rank of the process in his local communicator. So you will have two process of rank 0, one for each group, and so on.

重要的是要强调您的帖子的其他评论者在说什么:在当今构建程序时，请使用use mpi之类的现代结构代替include 'mpif.h'，请参见弗拉基米尔·F的评论.您上一个问题的另一条建议在两种情况下都使用等级0作为远程领导者.如果将这两个想法结合起来，您的程序将如下所示:

It is important to emphasize what other commentators of your post are saying: when building a program in those modern days, use moderns constructs like use mpi instead of include 'mpif.h' see comment from Vladimir F. Another advise from your previous question was yo use rank 0 as remote leader in both case. If I combine those 2 ideas, your program can look like:

program hello
use mpi !instead of include 'mpif.h'
implicit none

    integer :: tag,ierr,rank,numtasks,color,new_comm,inter1,inter2
    integer :: sendbuf,recvbuf,stat(MPI_STATUS_SIZE)
    integer :: irank
    !
    tag = 22
    sendbuf = 222
    !
    call MPI_Init(ierr)
    call MPI_COMM_RANK(MPI_COMM_WORLD,rank,ierr)
    call MPI_COMM_SIZE(MPI_COMM_WORLD,numtasks,ierr)
    !
    if (rank < 2) then
        color = 0
    else 
        color = 1
    end if
    !
    call MPI_COMM_SPLIT(MPI_COMM_WORLD,color,rank,new_comm,ierr)
    !
    if (color .eq. 0) then
        call MPI_INTERCOMM_CREATE(new_comm,0,MPI_Comm_world,2,tag,inter1,ierr)
    !
    call MPI_COMM_RANK(inter1,irank,ierr)
    if(irank==0)then
        call mpi_send(sendbuf,1,MPI_INT,0,tag,inter1,ierr)
    end if
    !
    else if(color .eq. 1) then
        call MPI_INTERCOMM_CREATE(new_comm,0,MPI_COMM_WORLD,0,tag,inter2,ierr)
        call MPI_COMM_RANK(inter2,irank,ierr)
        if(irank==0)then
            call mpi_recv(recvbuf,1,MPI_INT,0,tag,inter2,stat,ierr)
            if(ierr/=MPI_SUCCESS)print*,'Error in rec '
            print*,'rec buff = ', recvbuf
        end if
    end if
    !
    call MPI_finalize(ierr)
end program h

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