246. Window Info

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Hints specified via info (see Section The Info Object ) allow a user to provide information to direct optimization. Providing hints may enable an implementation to deliver increased performance or use system resources more efficiently. However, hints do not change the semantics of any MPI interfaces. In other words, an implementation is free to ignore all hints. Hints are specified on a per window basis, in window creation functions and MPI_WIN_SET_INFO, via the opaque info object. When an info object that specifies a subset of valid hints is passed to MPI_WIN_SET_INFO there will be no effect on previously set or default hints that the info does not specify.

Advice to implementors.

It may happen that a program is coded with hints for one system, and later executes on another system that does not support these hints. In general, unsupported hints should simply be ignored. Needless to say, no hint can be mandatory. However, for each hint used by a specific implementation, a default value must be provided when the user does not specify a value for the hint. ( End of advice to implementors.)

MPI_WIN_SET_INFO(win, info)
INOUT winwindow object (handle)
IN infoinfo object (handle)

int MPI_Win_set_info(MPI_Win win, MPI_Info info)
MPI_Win_set_info(win, info, ierror)
TYPE(MPI_Win), INTENT(IN) :: win
TYPE(MPI_Info), INTENT(IN) :: info

MPI_WIN_SET_INFO sets new values for the hints of the window associated with win. The call is collective on the group of win. The info object may be different on each process, but any info entries that an implementation requires to be the same on all processes must appear with the same value in each process's info object.

Advice to users.

Some info items that an implementation can use when it creates a window cannot easily be changed once the window has been created. Thus, an implementation may ignore hints issued in this call that it would have accepted in a creation call. ( End of advice to users.)

MPI_WIN_GET_INFO(win, info_used)
IN winwindow object (handle)
OUT info_usednew info object (handle)

int MPI_Win_get_info(MPI_Win win, MPI_Info *info_used)
MPI_Win_get_info(win, info_used, ierror)
TYPE(MPI_Win), INTENT(IN) :: win
TYPE(MPI_Info), INTENT(OUT) :: info_used

MPI_WIN_GET_INFO returns a new info object containing the hints of the window associated with win. The current setting of all hints actually used by the system related to this window is returned in info_used. If no such hints exist, a handle to a newly created info object is returned that contains no key/value pair. The user is responsible for freeing info_used via MPI_INFO_FREE.

Advice to users.

The info object returned in info_used will contain all hints currently active for this window. This set of hints may be greater or smaller than the set of hints specified when the window was created, as the system may not recognize some hints set by the user, and may recognize other hints that the user has not set. ( End of advice to users.)

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