MPI_Win_shared_query(3) Query the size and base pointer for a patch of a shared memory window.


int MPI_Win_shared_query(MPI_Win win, int rank, MPI_Aint *size, int *disp_unit, void *baseptr)

This function queries the process-local address for remote memory segments created with MPI_Win_allocate_shared . This function can return different process-local addresses for the same physical memory on different processes.

The returned memory can be used for load/store accesses subject to the constraints defined in MPI 3.0, Section 11.7. This function can only be called with windows of type MPI_Win_flavor_shared . If the passed window is not of flavor MPI_Win_flavor_shared , the error MPI_ERR_RMA_FLAVOR is raised. When rank is MPI_PROC_NULL , the pointer, disp_unit, and size returned are the pointer, disp_unit, and size of the memory segment belonging the lowest rank that specified size > 0. If all processes in the group attached to the window specified size = 0, then the call returns size = 0 and a baseptr as if MPI_Alloc_mem was called with size = 0.


- window object used for communication (handle)
- target rank


- size of the segment at the given rank
- local unit size for displacements, in bytes (positive integer)
- base pointer in the calling process' address space of the shared segment belonging to the target rank.


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.


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 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 MPI window object