MPI + C broadcast operation

Int mpi_bcast (void * buffer, int count, mpi_datatype datatype, int root, mpi_comm comm)

Mpi_bcast must be called during blocking communication;

You also need to call mpi_bcast when receiving the message and check whether the Root parameter is the same as your own ID number. If the Root parameter is different, the message is received;

 

 

1. broadcast an element in the main process array and output it at the corresponding position in the other process array.

 

 

# Include "MPI. H "<br/> # include <stdio. h> <br/> const int n = 10; <br/> int main (INT argc, char * argv []) {<br/> int I, rank, numprocs, master; <br/> int DP [N]; <br/> mpi_init (& argc, & argv); <br/> mpi_comm_rank (mpi_comm_world, & rank ); <br/> mpi_comm_size (mpi_comm_world, & numprocs); <br/> for (I = 0; I <n; I ++) {<br/> DP [I] = rank; <br/>}< br/> // DP [Rank] = rank; </P> <p> If (Rank = Master) mpi_bcast (& DP [Master], 1, mpi_int, Master, mpi_comm_world ); </P> <p> mpi_bcast (& DP [Master], 1, mpi_int, Master, mpi_comm_world); <br/> If (Rank = numprocs-1) {<br/> for (I = 0; I <n; I ++) <br/> printf ("% d", DP [I]); <br/> printf ("/N"); <br/>}</P> <p> mpi_finalize (); <br/> return 0; <br/>} 

Result:

[Root @ c0101 ~] # Mpicxx bcast. cpp-o a <br/> [root @ c0101 ~] # Mpiexec-N 5./A <br/> 0 4 4 4 4 4 4 4 4 4 4 <br/> [root @ c0101 ~] # 

 

 

 

2. Read a value from the main process, broadcast it, and output it.

 

# Include "MPI. H "<br/> # include <stdio. h> <br/> int main (INT argc, char * argv []) {<br/> int I, rank, numprocs, master; <br/> int value =-1; <br/> mpi_init (& argc, & argv); <br/> mpi_comm_rank (mpi_comm_world, & rank ); <br/> mpi_comm_size (mpi_comm_world, & numprocs); </P> <p> If (Rank = Master) {<br/> printf ("Please input a positive value: "); <br/> scanf (" % d ", & value); <br/> mpi_bcast (& Value, 1, mpi_int, Master, mpi_comm_world ); <br/>}</P> <p> mpi_bcast (& Value, 1, mpi_int, Master, mpi_comm_world); </P> <p> mpi_barrier (mpi_comm_world ); <br/> printf ("value of process % d is: % d/N", rank, value); <br/> mpi_finalize (); <br/> return 0; <br/>} 

Result:

[Root @ c0101 ~] # Mpicxx bcast. cpp-o a <br/> [root @ c0101 ~] # Mpiexec-N 5. /A <br/> Please input a positive value: 8 <br/> value of process 2 is: 8 <br/> value of process 0 is: 8 <br/> value of process 3 is: 8 <br/> value of process 4 is: 8 <br/> value of process 1 is: 8 <br/> [root @ c0101 ~] # 

 

 

In addition, the following deadlock occurs. In fact, it can be replaced by non-blocking communication mpi_isend.

Program Main <br/> implicit none <br/> include 'mpif. h' <br/> integer, parameter: n = 10 <br/> integer myid, numprocs, ierr, I <br/> integer dp (0: 10) <br/> call mpi_init (ierr) <br/> call mpi_comm_rank (mpi_comm_world, myid, ierr) <br/> call mpi_comm_size (mpi_comm_world, numprocs, ierr) <br/> do I = 0, n <br/> dp (I) =-1 <br/> enddo <br/> dp (myid) = myid <br/> call mpi_barrier (mpi_comm_world, ierr) <br/> If (myid. ne. numprocs-1) Call mpi_bcast (dp (myid), 1, mpi_integer, <br/> & myid, mpi_comm_world, ierr) <br/> If (myid. eq. (numprocs-1) Then <br/> do I = 0, numprocs-2 <br/> call mpi_bcast (dp (I), 1, mpi_integer, I, <br/> & mpi_comm_world, ierr) <br/> enddo <br/> Print *, dp <br/> endif <br/> call mpi_finalize (ierr) <br/> end