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Subject: [OMPI devel] Bug (wrong LB?) when using cascading derived data types
From: Markus Blatt (Markus.Blatt_at_[hidden])
Date: 2009-03-02 10:04:59


Hi,

I already posted this accidentally on the users list, but as it seems
like a bug I suppose this list is more appropriated.

In one of my applications I am using cascaded derived MPI datatypes
created with MPI_Type_struct. One of these types is used to just send
a part (one MPI_Char) of a struct consisting of an int followed by two
chars. I.e, the int at the beginning is/should be ignored.

This works fine if I use this data type on its own.

Unfortunately I need to send another struct that contains an int and
the int-char-char struct from above. Again I construct a custom MPI
data type for this.

When sending this cascaded data type It seems that the offset of the
char in the inner custom type is disregarded on the receiving end and
the
received data ('1') is stored in the first int instead of the
following char.

I have tested this code with both lam and mpich. There it worked as
expected (saving the '1' in the first char).

The last two lines of the output of the attached test case read

received global=10 attribute=0 (local=1 public=0)
received attribute=1 (local=100 public=0)

for openmi instead of

received global=10 attribute=1 (local=100 public=0)
received attribute=1 (local=100 public=0)

for lam and mpich.

This problem is experienced when using version 1.3-2 as well as
1.2.7~rc2-2 of openmpi on Debian.
At first sight it seemed corellated with bug #1677. But as that should
be fixed since 1.2.9 it is probably something else.

Cheers,

Markus

#include"mpi.h"
#include<iostream>

struct LocalIndex
{
  int local_;
  char attribute_;
  char public_;
};

struct IndexPair
{
  int global_;
  LocalIndex local_;
};
  

int main(int argc, char** argv)
{
  MPI_Init(&argc, &argv);

  int rank, size;
  
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  if(size<2)
    {
      std::cerr<<"no procs has to be >2"<<std::endl;
      MPI_Abort(MPI_COMM_WORLD, 99);
    }
  
  MPI_Datatype litype, ptype;
  // Create custom MPI datatypes
  {
    int length=1;
    MPI_Aint disp, origin, next;
    MPI_Datatype types = MPI_CHAR;
    LocalIndex rep[2];
    MPI_Address(rep, &origin); // lower bound of the datatype
    MPI_Address(&(rep[0].attribute_), &disp);
    MPI_Address(rep+1, &next);
    
    disp -= origin;
    next -= origin;
    MPI_Datatype tmptype;
    MPI_Type_struct(1, &length, &disp, &types, &litype);
    //MPI_Type_commit(&tmptype);
    //MPI_Type_create_resized(tmptype, (MPI_Aint)0, next, &litype);
    MPI_Type_commit(&litype);
    //MPI_Type_free(&tmptype);

    if(rank==0)
      {
        MPI_Aint lb,extent;
        MPI_Type_get_extent(litype, &lb, &extent);
        std::cout<<"litype: lb="<<lb<<" extend="<<extent<<std::endl;
        MPI_Type_get_true_extent(litype, &lb, &extent);
        std::cout<<"true litype: lb="<<lb<<" extend="<<extent<<std::endl;
        int size;
        MPI_Type_size(litype, &size);
        std::cout<<"litype size="<<size<<std::endl;
      }
  }
  
  {
    int length[2] ={1, 1};
    MPI_Aint disp[2], origin;
    MPI_Datatype types[2] = {MPI_INT,
                             litype};
    IndexPair rep[2];

    MPI_Address(rep, &origin); // lower bound of the datatype
    MPI_Address(&(rep[0].global_), disp);
    MPI_Address(&(rep[0].local_), disp+1);
    for(int i=0; i < 2; ++i)
      disp[i] -= origin;
    MPI_Type_struct(2, length, disp, types, &ptype);
    MPI_Type_commit(&ptype);
    if(rank==0)
      {
        MPI_Aint lb,extent;
        MPI_Type_get_extent(ptype, &lb, &extent);
        std::cout<<"ptype: lb="<<lb<<" extend="<<extent<<std::endl;
        MPI_Type_get_true_extent(ptype, &lb, &extent);
        std::cout<<"true: ptype: lb="<<lb<<" extend="<<extent<<std::endl;
        int size;
        MPI_Type_size(ptype, &size);
        std::cout<<"ptype size="<<size<<std::endl;
        
      }
  }
  
  IndexPair pair;

  if(rank==0)
    {
      pair.global_=10;
      pair.local_.local_=1;
      pair.local_.attribute_='1';
      pair.local_.public_='1';
      MPI_Send(&pair, 1, ptype, 1, 199, MPI_COMM_WORLD);
      MPI_Send(&pair.local_, 1, litype, 1, 199, MPI_COMM_WORLD);
    }else
    {
      pair.global_=0;
      pair.local_.local_=100;
      pair.local_.attribute_='0';
      pair.local_.public_='0';
      if(rank==1)
        {
          MPI_Status status;
          MPI_Recv(&pair, 1, ptype, 0, 199, MPI_COMM_WORLD, &status);
          std::cout<<"received global="<<pair.global_<<" attribute="<<
            pair.local_.attribute_<<" (local="<<pair.local_.local_
                   <<" public="<<pair.local_.public_<<")"<<std::endl;
          
          pair.local_.local_=100;
          pair.local_.attribute_='0';
          pair.local_.public_='0';
          MPI_Recv(&pair.local_, 1, litype, 0, 199, MPI_COMM_WORLD, &status);
          std::cout<<"received attribute="<<pair.local_.attribute_
                   <<" (local="<<pair.local_.local_
                   <<" public="<<pair.local_.public_<<")"<<std::endl;
        }
    }
  MPI_Barrier(MPI_COMM_WORLD);
  MPI_Finalize();
  
}

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