MPI Bcast with MPI_Type_create_struct segmentation fault

Question

I'm forcing myself to do a broadcast with a personal struct in C-language MPI. Basically I've created the struct Vector3d.

typedef struct {
    double x, y, z;
} Vector3d;

Then i've been reading and code this for each MPI Process.

int rank, size;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);

// MPI Struct para Vector3d
int nroItems = 3;
int blockLengths[3] = { 1, 1, 1 };
MPI_Datatype types[3] = { MPI_DOUBLE, MPI_DOUBLE, MPI_DOUBLE };
MPI_Datatype MPI_Vector3d;
MPI_Aint     offsets[3];
offsets[0] = offsetof(Vector3d, x);
offsets[1] = offsetof(Vector3d, y);
offsets[3] = offsetof(Vector3d, z);

MPI_Type_create_struct(nroItems, blockLengths, offsets, types, &MPI_Vector3d);
MPI_Type_commit(&MPI_Vector3d);

Then i do the broadcast of an array of Vector3d with this.

Vector3d * num = (Vector3d *) malloc(sizeof(Vector3d) * 10);
if(rank == 0) {
    ... 
    ...
    MPI_Bcast(num, 10, MPI_Vector3d, 0, MPI_COMM_WORLD);
} else {
    MPI_Bcast(num, 10, MPI_Vector3d, 0, MPI_COMM_WORLD);
}

And i've got this when i run it.

[mario-elementary:24020] *** Process received signal ***
[mario-elementary:24020] Signal: Segmentation fault (11)
[mario-elementary:24020] Signal code: Address not mapped (1)
[mario-elementary:24020] Failing at address: 0x56fae13e2cc8
[mario-elementary:24020] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0xfcb0) [0x2b7d6fce7cb0]
[mario-elementary:24020] [ 1] /lib/x86_64-linux-gnu/libc.so.6(+0x14ae90) [0x2b7d70040e90]
[mario-elementary:24020] [ 2] /usr/lib/libmpi.so.0(+0x3f812) [0x2b7d6fa67812]
...
...etc
--------------------------------------------------------------------------
mpirun noticed that process rank 0 with PID 24020 on node mario-elementary exited on signal 11 (Segmentation fault).
--------------------------------------------------------------------------

Please help!

In the MPI_Bcast call in the else part, you mention root value as 0, shouldn't that be a nonzero rank? — Ketan
– Ketan, Commented Dec 25, 2013 at 21:25

Jonas Bötel · Accepted Answer · 2013-12-25 21:31:26Z

1

There is a typo in your offsets

offsets[3] = offsetof(Vector3d, z);

Should be offset[2] instead. I guess that and fixing the bcast problem is all it takes.

Also what is the result of your offsetof function? How does it work?

answered Dec 25, 2013 at 21:31

Jonas Bötel

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1 Comment

Mario Luis Over a year ago

Yep! There was the seg fault... Thanks!

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