MPI_File_set_atomicity(3)

NAME
     MPI_File_set_atomicity - Sets the atomicity mode

SYNOPSIS
     C:

          #include "mpi.h"

          int MPI_File_set_atomicity(MPI_File fh, int flag)


     Fortran:

          INCLUDE "mpif.h" (or USE MPI)

          INTEGER fh, ierror
          LOGICAL flag

          CALL MPI_FILE_SET_ATOMICITY(fh, flag, ierror)


DESCRIPTION
     MPI_File_set_atomicity sets the atomicity mode.  Let fh be the set of
     file handles created by one collective open operation. This routine
     accepts the following arguments:

     fh        Specifies the file handle (handle)

     flag      Indicates true to set atomic mode, false to set nonatomic mode
               (logical)

     ierror    Specifies the return code value for successful completion,
               which is in MPI_SUCCESS.  MPI_SUCCESS is defined in the mpif.h
               file.

     You can set the consistency semantics for data access operations that use
     fh by collectively calling MPI_File_set_atomicity on fh.
     MPI_File_set_atomicity is collective; all processes in the group must
     pass identical values for fh and flag.  If flag is true, atomic mode is
     set; if flag is false, nonatomic mode is set.

     Changing the consistency semantics for an open file affects only new data
     accesses.  All completed data accesses are guaranteed to abide by the
     consistency semantics in effect during their execution.  Nonblocking data
     accesses and split collective operations that have not completed (for
     example, because of MPI_WAIT) are guaranteed to abide only by nonatomic
     mode consistency semantics.

     Because the semantics guaranteed by atomic mode are stronger than those
     guaranteed by nonatomic mode, an implementation is free to adhere to the
     more stringent atomic mode semantics for outstanding requests.
   Notes for Fortran
     All MPI objects (for example, MPI_Datatype, MPI_Comm, MPI_File) are of
     type INTEGER.

SEE ALSO
     MPI_File_open(3), MPI_IO(3)