The Great and Terrible implementation of MPI-2

function index


Put data into a memory window on a remote process
int MPI_Put(
  void *origin_addr,
  int origin_count,
  MPI_Datatype origin_datatype,
  int target_rank,
  MPI_Aint target_disp,
  int target_count,
  MPI_Datatype target_datatype,
  MPI_Win win


[in] initial address of origin buffer (choice)
[in] number of entries in origin buffer (nonnegative integer)
[in] datatype of each entry in origin buffer (handle)
[in] rank of target (nonnegative integer)
[in] displacement from start of window to target buffer (nonnegative integer)
[in] number of entries in target buffer (nonnegative integer)
[in] datatype of each entry in target buffer (handle)  
[in] window object used for communication (handle)


The execution of a put operation is similar to the execution of a send by the origin process and a matching receive by the target process. The obvious difference is that all arguments are provided by one call --- the call executed by the origin process.

Transfers origin_count successive entries of the type specified by the origin_datatype, starting at address origin_addr on the origin node to the target node specified by the win, target_rank pair. The data are written in the target buffer at address target_addr = window_base + target_dispdisp_unit, where window_base and disp_unit are the base address and window displacement unit specified at window initialization, by the target process.

The target buffer is specified by the arguments target_count and target_datatype.

The data transfer is the same as that which would occur if the origin process executed a send operation with arguments origin_addr, origin_count, origin_datatype, target_rank, tag, comm, and the target process executed a receive operation with arguments target_addr, target_count, target_datatype, source, tag, comm, where target_addr is the target buffer address computed as explained above, and comm is a communicator for the group of win.

The communication must satisfy the same constraints as for a similar message-passing communication. The target_datatype may not specify overlapping entries in the target buffer. The message sent must fit, without truncation, in the target buffer. Furthermore, the target buffer must fit in the target window.

The target_datatype argument is a handle to a datatype object defined at the origin process. However, this object is interpreted at the target process: the outcome is as if the target datatype object was defined at the target process, by the same sequence of calls used to define it at the origin process. The target datatype must contain only relative displacements, not absolute addresses. The same holds for get and accumulate.

Advice to users.

The target_datatype argument is a handle to a datatype object that is defined at the origin process, even though it defines a data layout in the target process memory. This causes no problems in a homogeneous environment, or in a heterogeneous environment, if only portable datatypes are used.

The performance of a put transfer can be significantly affected, on some systems, from the choice of window location and the shape and location of the origin and target buffer: transfers to a target window in memory allocated by MPI_ALLOC_MEM may be much faster on shared memory systems; transfers from contiguous buffers will be faster on most, if not all, systems; the alignment of the communication buffers may also impact performance.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid MPI window object

Example Code

The following sample code illustrates MPI_Put.

#include "mpi.h"
#include "stdio.h"
/* tests put and get with post/start/complete/wait on 2 processes */
#define SIZE1 100
#define SIZE2 200
int main(int argc, char *argv[])
int rank, destrank, nprocs, *A, *B, i;
    MPI_Group comm_group, group;
    MPI_Win win;
int errs = 0;
if (nprocs != 2) {
        printf("Run this program with 2 processes\n");fflush(stdout);
    i = MPI_Alloc_mem(SIZE2 *
sizeof(int), MPI_INFO_NULL, &A);
if (i) {
        printf("Can't allocate memory in test program\n");fflush(stdout);
        MPI_Abort(MPI_COMM_WORLD, 1);
    i = MPI_Alloc_mem(SIZE2 *
sizeof(int), MPI_INFO_NULL, &B);
if (i) {
        printf("Can't allocate memory in test program\n");fflush(stdout);
        MPI_Abort(MPI_COMM_WORLD, 1);

    MPI_Comm_group(MPI_COMM_WORLD, &comm_group);
    if (rank == 0) {
        for (i=0; i<SIZE2; i++) A[i] = B[i] = i;
        MPI_Win_create(NULL, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win);
        destrank = 1;
        MPI_Group_incl(comm_group, 1, &destrank, &group);
        MPI_Win_start(group, 0, win);
        for (i=0; i<SIZE1; i++)
            MPI_Put(A+i, 1, MPI_INT, 1, i, 1, MPI_INT, win);
for (i=0; i<SIZE1; i++)
            MPI_Get(B+i, 1, MPI_INT, 1, SIZE1+i, 1, MPI_INT, win);
for (i=0; i<SIZE1; i++)
if (B[i] != (-4)*(i+SIZE1)) {
                printf("Get Error: B[i] is %d, should be %d\n", B[i], (-4)*(i+SIZE1));fflush(stdout);
    else { /* rank=1 */
        for (i=0; i<SIZE2; i++) B[i] = (-4)*i;
        MPI_Win_create(B, SIZE2*
sizeof(int), sizeof(int), MPI_INFO_NULL, MPI_COMM_WORLD, &win);
        destrank = 0;
        MPI_Group_incl(comm_group, 1, &destrank, &group);
        MPI_Win_post(group, 0, win);

        for (i=0; i<SIZE1; i++) {
            if (B[i] != i) {
                printf("Put Error: B[i] is %d, should be %d\n", B[i], i);fflush(stdout);
return errs;