When a window is created, the base, size, and displacement units of the window are cached and can be retrieved by using the MPI_Win_get_attr call.

int MPI_Win_get_attr(MPI_Win win, int win_keyval, void *attribute_val, int *flag)

win

the instantiated window object

win_keyval

One of (MPI_WIN_BASE, MPI_WIN_SIZE, MPI_WIN_DISP_UNIT)

attribute_val

the requested attribute value (unless the flag is false)

flag

whether a value is associated with the requested attribute key

When the window is open, it is available to members of an MPI group. It is possible to retrieve the group of processes that is attached to a particular window in the current epoch using the MPI_Win_get_group call.

int MPI_Win_get_group(MPI_Win win, MPI_Group *group)

win

the instantiated window object

group

the group associated with the provided window (out)