MPI_Neighbor_alltoall(3) MPI MPI_Neighbor_alltoall(3) NAME MPI_Neighbor_alltoall - Sends and Receivs data from all neighboring processes SYNOPSIS int MPI_Neighbor_alltoall(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, int recvcount, MPI_Datatype recvtype, MPI_Comm comm) int MPI_Neighbor_alltoall_c(const void *sendbuf, MPI_Count sendcount, MPI_Datatype sendtype, void *recvbuf, MPI_Count recvcount, MPI_Datatype recvtype, MPI_Comm comm) INPUT PARAMETERS sendbuf - starting address of send buffer (choice) sendcount - number of elements sent to each neighbor (non-negative integer) sendtype - data type of send buffer elements (handle) recvcount - number of elements received from each neighbor (non-negative inte- ger) recvtype - data type of receive buffer elements (handle) comm - communicator with topology structure (handle) OUTPUT PARAMETERS recvbuf - starting address of receive buffer (choice) NOTES In this function, each process i receives data items from each process j if an edge (j,i) exists in the topology graph or Cartesian topology. Simi- larly, each process i sends data items to all processes j where an edge (i,j) exists. This call is more general than MPI_NEIGHBOR_ALLGATHER in that different data items can be sent to each neighbor. The k-th block in send buffer is sent to the k-th neighboring process and the l-th block in the receive buffer is received from the l-th neighbor. 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 inte- ger 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 state- ment. All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran. ERRORS 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 ar- gument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error han- dler 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 guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. MPI_SUCCESS - No error; MPI routine completed successfully. MPI_ERR_BUFFER - Invalid buffer pointer. Usually a null buffer where one is not valid. MPI_ERR_COMM - Invalid communicator. A common error is to use a null communica- tor in a call (not even allowed in MPI_Comm_rank ). MPI_ERR_COUNT - Invalid count argument. Count arguments must be non-negative; a count of zero is often valid. MPI_ERR_TYPE - Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit ) is used in a com- munication call. MPI_ERR_OTHER - Other error; use MPI_Error_string to get more information about this error code. 4/10/2026 MPI_Neighbor_alltoall(3)
NAME | SYNOPSIS | INPUT PARAMETERS | OUTPUT PARAMETERS | NOTES | THREAD AND INTERRUPT SAFETY | NOTES FOR FORTRAN | ERRORS
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