# 17.2.459. MPI_Win_shared_query

MPI_Win_shared_query — Query a shared memory window

## 17.2.459.1. SYNTAX

### 17.2.459.1.1. C Syntax

    #include <mpi.h>

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

### 17.2.459.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_WIN_SHARED_QUERY(WIN, RANK, SIZE, DISP_UNIT, BASEPTR, IERROR)
            INTEGER WIN, RANK, DISP_UNIT, IERROR
            INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR

### 17.2.459.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Win_shared_query(win, rank, size, disp_unit, baseptr, ierror)
         USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_PTR
         TYPE(MPI_Win), INTENT(IN) :: win
         INTEGER, INTENT(IN) :: rank
         INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: size
         INTEGER, INTENT(OUT) :: disp_unit
         TYPE(C_PTR), INTENT(OUT) :: baseptr
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 17.2.459.2. INPUT PARAMETERS

- `win`: Shared memory window object (handle).

- `rank`: Rank in the group of window win (non-negative integer) or `MPI_PROC_NULL`.

## 17.2.459.3. OUTPUT PARAMETERS

- `size`: Size of the window segment (non-negative integer).

- `disp_unit`: Local unit size for displacements, in bytes (positive integer).

- `baseptr`: Address for load/store access to window segment (choice).

- `ierror`: Fortran only: Error status (integer).

## 17.2.459.4. DESCRIPTION

MPI_Win_shared_query 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-3.1 section 11.7. This function can only be called with windows of flavor 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.

## 17.2.459.5. C NOTES

The parameter baseptr is of type `void *` to allow passing any pointer object for this parameter. The provided argument should be a pointer to a pointer of arbitrary type (e.g. `void **`).

## 17.2.459.6. ERRORS

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

- `MPI_ERRORS_ARE_FATAL` Causes the program to abort all connected MPI processes.

- `MPI_ERRORS_ABORT` An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.

- `MPI_ERRORS_RETURN` Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

- MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

- MPI_File_create_errhandler then MPI_File_set_errhandler

- MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

- MPI_Win_create_errhandler then MPI_Win_set_errhandler

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3.1 standard for more information.

See also

- MPI_Alloc_mem

- MPI_Win_allocate_shared