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

问题描述

在以下代码中，如果我没有将xysize的值声明为参数(通常我不能这样做)，则该值会更改.仅在优化-O2以及gfortran 4.7.2和OpenMPI 1.6中的其他情况下才会发生这种情况.这怎么可能?我找不到从mpi.mod导入的确切接口，但是C原型清楚地指出count是按值传递的，因此它不能更改.

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

为了将来的访问者，我想我会回答这个问题，即使上面的评论中都回答了这些问题.

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，则无法在对MPI_Recv的调用中更改该参数的值(计数").

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.

您的参数status太小，它应该是数组status(MPI_STATUS_SIZE)，并且您会遇到缓冲区溢出-这通常会导致分段错误，但有时(取决于编译器如何打包)内存中的变量)，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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