Databases Reference
In-Depth Information
sleep
(
random
()
*
5
)
print
"A (rank
%d
)"
%
rank
sleep
(
random
()
*
5
)
print
"B (rank
%d
)"
%
rank
Running it, we get:
$ mpiexec -n 4 python demo2.py
A (rank 2)
B (rank 2)
A (rank 1)
A (rank 0)
B (rank 1)
A (rank 3)
B (rank 3)
B (rank 0)
Our
COMM_WORLD
communicator includes a
Barrier
function. If we add a barrier for all
processes just before the “B” print statement, we get:
from
random
import
random
from
time
import
sleep
from
mpi4py
import
MPI
comm
=
MPI
.
COMM_WORLD
rank
=
comm
.
rank
sleep
(
random
()
*
5
)
print
"A (rank
%d
)"
%
rank
comm
.
Barrier
()
# Blocks until all processes catch up
sleep
(
random
()
*
5
)
print
"B (rank
%d
)"
%
rank
$ mpiexec -n 4 python demo3.py
A (rank 2)
A (rank 3)
A (rank 0)
A (rank 1)
B (rank 2)
B (rank 0)
B (rank 1)
B (rank 3)
Now that you know about
Barrier
, what do you think the following two-process pro‐
gram outputs?
import
h5py
from
mpi4py
import
MPI
comm
=
MPI
.
COMM_WORLD
rank
=
comm
.
rank
