rank 0为master其余都是slave
http://www.lam-mpi.org/tutorials/one-step/ezstart.php
~~~
#include <mpi.h>
#define WORKTAG 1
#define DIETAG 2
/* Local functions */
static void master(void);
static void slave(void);
static unit_of_work_t get_next_work_item(void);
static void process_results(unit_result_t result);
static unit_result_t do_work(unit_of_work_t work);
int
main(int argc, char **argv)
{
int myrank;
/* Initialize MPI */
MPI_Init(&argc, &argv);
/* Find out my identity in the default communicator */
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
if (myrank == 0) {
master();
} else {
slave();
}
/* Shut down MPI */
MPI_Finalize();
return 0;
}
static void
master(void)
{
int ntasks, rank;
unit_of_work_t work;
unit_result_t result;
MPI_Status status;
/* Find out how many processes there are in the default
communicator */
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
/* Seed the slaves; send one unit of work to each slave. */
for (rank = 1; rank < ntasks; ++rank) {
/* Find the next item of work to do */
work = get_next_work_item();
/* Send it to each rank */
MPI_Send(&work, /* message buffer */
1, /* one data item */
MPI_INT, /* data item is an integer */
rank, /* destination process rank */
WORKTAG, /* user chosen message tag */
MPI_COMM_WORLD); /* default communicator */
}
/* Loop over getting new work requests until there is no more work
to be done */
work = get_next_work_item();
while (work != NULL) {
/* Receive results from a slave */
MPI_Recv(&result, /* message buffer */
1, /* one data item */
MPI_DOUBLE, /* of type double real */
MPI_ANY_SOURCE, /* receive from any sender */
MPI_ANY_TAG, /* any type of message */
MPI_COMM_WORLD, /* default communicator */
&status); /* info about the received message */
/* Send the slave a new work unit */
MPI_Send(&work, /* message buffer */
1, /* one data item */
MPI_INT, /* data item is an integer */
status.MPI_SOURCE, /* to who we just received from */
WORKTAG, /* user chosen message tag */
MPI_COMM_WORLD); /* default communicator */
/* Get the next unit of work to be done */
work = get_next_work_item();
}
/* There's no more work to be done, so receive all the outstanding
results from the slaves. */
for (rank = 1; rank < ntasks; ++rank) {
MPI_Recv(&result, 1, MPI_DOUBLE, MPI_ANY_SOURCE,
MPI_ANY_TAG, MPI_COMM_WORLD, &status);
}
/* Tell all the slaves to exit by sending an empty message with the
DIETAG. */
for (rank = 1; rank < ntasks; ++rank) {
MPI_Send(0, 0, MPI_INT, rank, DIETAG, MPI_COMM_WORLD);
}
}
static void
slave(void)
{
unit_of_work_t work;
unit_result_t results;
MPI_Status status;
while (1) {
/* Receive a message from the master */
MPI_Recv(&work, 1, MPI_INT, 0, MPI_ANY_TAG,
MPI_COMM_WORLD, &status);
/* Check the tag of the received message. */
if (status.MPI_TAG == DIETAG) {
return;
}
/* Do the work */
result = do_work(work);
/* Send the result back */
MPI_Send(&result, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
}
}
static unit_of_work_t
get_next_work_item(void)
{
/* Fill in with whatever is relevant to obtain a new unit of work
suitable to be given to a slave. */
}
static void
process_results(unit_result_t result)
{
/* Fill in with whatever is relevant to process the results returned
by the slave */
}
static unit_result_t
do_work(unit_of_work_t work)
{
/* Fill in with whatever is necessary to process the work and
generate a result */
}
~~~
