MPI_Recv 覆盖它不应访问的部分内存 [英] MPI_Recv overwrites parts of memory it should not access

问题描述

在下面的代码中，xysize 的值会发生变化，如果我不将其声明为参数(我通常不能这样做).它只发生在 gfortran 4.7.2 和 OpenMPI 1.6 中的优化 -O2 和更多.这怎么可能?我找不到从 mpi.mod 导入的确切接口，但 C 原型明确指出 count 是按值传递的，因此它无法更改.

In the following code the value of xysize gets changed, if I do not declare it as a parameter (which I generally cannot do). It happens only with optimizations -O2 and more in gfortran 4.7.2 and OpenMPI 1.6. How is it possible? I cannot find the exact interface, that I import from mpi.mod, but the C prototype clearly states that count is passed by value, hence it cannot change.

     write(*,*) im,"receiving from",image_index([iim,jim,kim+1]),"size",&
      size(D%A(D%starti:D%endi,D%startj:D%endj,D%endk)),xysize

    call MPI_RECV(D%A(D%starti:D%endi,D%startj:D%endj,D%endk+1),xysize , MPI_REAL, image_index([iim,jim,kim+1])-1,&
           5000, comm, status, ierr)

    write(*,*) im,"received size",&
      size(D%A(D%starti:D%endi,D%startj:D%endj,D%endk)),xysize

输出:

1 receiving from           2 size        4096        4096
1 received size        4096        5000

推荐答案

为了以后的访问者，我想我会回答这个问题，即使上面的评论都回答了.

For the sake of future visitors, I suppose I'll answer this even though it's all answered in the comments above.

据我所知，如果您的程序运行正常，则无法在调用 MPI_Recv 时更改该参数(count")的值.

As far as I'm aware, if your program is behaving properly, you cannot change the value of that parameter ("count") in a call to MPI_Recv.

你的参数 status 太小，它应该是一个数组 status(MPI_STATUS_SIZE)，你得到一个缓冲区溢出——这通常会导致分段错误，但有时(取决于编译器如何将变量打包到内存中)，它可能会导致类似这样的有趣行为.

Your argument status is too small, it should be an array status(MPI_STATUS_SIZE), and you're getting a buffer overflow -- This often results in a segmentation fault, but at times (depending on how the compiler packed the variables in memory), it can result in funny behavior like this.

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