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Subject: [OMPI users] Error message when using MPI_Datatype_struct()
From: Thomas Ropars (tropars_at_[hidden])
Date: 2008-03-10 05:54:47


Hi,

I'm currently implementing a mechanism to piggyback information on
messages. On message sending, I dynamically create a new datatype
composed of the original buffer and of the data to piggyback.

For instance, if I want to piggyback an integer on each message, I use
the following code:

int send(void *buf,
         size_t count,
         struct ompi_datatype_t* datatype,
         int dst,
         int tag,
         mca_pml_base_send_mode_t sendmode,
         ompi_communicator_t* comm )
{
    MPI_Datatype type[2];
    int blocklen[2];
    MPI_Aint disp[2];
    MPI_Datatype datatype_out;
    int piggy=0;

    type[0]=datatype;
    type[1]=MPI_INT;
    blocklen[0]=count;
    blocklen[1]=1;

    MPI_Address(buf,disp);
    MPI_Address(&piggy,disp+1);

    MPI_Type_struct(2, blocklen, disp, type, datatype_out);

    MPI_Type_commit(datatype_out);

    /* then I call the original send function and send my new datatype */
    original_send(MPI_BOTTOM, 1, datatype_out, dst, tag, sendmode,
                  comm);

}

This code works well. But if the data I want to piggyback is dynamically
allocated. I get this kind of error message:

../../ompi/datatype/datatype_pack.h:40
        Pointer 0x823fab0 size 4 is outside [0xbfef8920,0x823fab4] for
        base ptr (nil) count 1 and data
Datatype 0x8240b90[] size 8 align 4 id 0 length 3 used 2
true_lb -1074820832 true_ub 136575668 (true_extent 1211396500) lb
-1074820832 ub 136575668 (extent 1211396500)
nbElems 2 loops 0 flags 102 (commited )-c-----GD--[---][---

Despite this message, the function works well too ...

Can someone explain me what this message means ? It seems that in the
first part of the error message, the lower bound and the upper bound of
the datatype are switched, but I don't know why.

Regards.

Thomas Ropars