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<TITLE>MPI_Win_allocate_shared</TITLE>
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MPI_Win_allocate_shared
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Create an MPI Window object for one-sided communication and shared memory access, and allocate memory at each process.
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Synopsis
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int MPI_Win_allocate_shared(MPI_Aint size, int disp_unit, MPI_Info info, MPI_Comm comm,
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void *baseptr, MPI_Win * win)
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This is a collective call executed by all processes in the group of comm. On
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each process i, it allocates memory of at least size bytes that is shared among
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all processes in comm, and returns a pointer to the locally allocated segment
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in baseptr that can be used for load/store accesses on the calling process. The
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locally allocated memory can be the target of load/store accesses by remote
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processes; the base pointers for other processes can be queried using the
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function <tt>MPI_Win_shared_query</tt>.
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The call also returns a window object that can be used by all processes in comm
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to perform RMA operations. The size argument may be different at each process
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and size = 0 is valid. It is the user's responsibility to ensure that the
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communicator comm represents a group of processes that can create a shared
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memory segment that can be accessed by all processes in the group. The
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allocated memory is contiguous across process ranks unless the info key
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alloc_shared_noncontig is specified. Contiguous across process ranks means that
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the first address in the memory segment of process i is consecutive with the
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last address in the memory segment of process i − 1. This may enable the user
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to calculate remote address offsets with local information only.
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Input Parameters
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size size of window in bytes (nonnegative integer)
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disp_unit local unit size for displacements, in bytes (positive integer)
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info info argument (handle)
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comm communicator (handle)
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Output Parameters
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baseptr initial address of window (choice)
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win window object returned by the call (handle)
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Thread and Interrupt Safety
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This routine is thread-safe. This means that this routine may be
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safely used by multiple threads without the need for any user-provided
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thread locks. However, the routine is not interrupt safe. Typically,
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this is due to the use of memory allocation routines such as <tt>malloc
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</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
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Notes for Fortran
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All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
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an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
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</tt>is an integer and has the same meaning as the return value of the routine
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in C. In Fortran, MPI routines are subroutines, and are invoked with the
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<tt>call</tt> statement.
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All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
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</tt>in Fortran.
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Errors
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All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
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C routines as the value of the function and Fortran routines in the last
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argument. Before the value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job. The error handler
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may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
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<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
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RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
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its use is deprecated. The predefined error handler
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<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
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Note that MPI does not guarentee that an MPI program can continue past
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an error; however, MPI implementations will attempt to continue whenever
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possible.
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MPI_SUCCESS No error; MPI routine completed successfully.
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MPI_ERR_ARG Invalid argument. Some argument is invalid and is not
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identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
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MPI_ERR_COMM Invalid communicator. A common error is to use a null
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communicator in a call (not even allowed in <tt>MPI_Comm_rank</tt>).
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MPI_ERR_INFO Invalid Info
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MPI_ERR_OTHER Other error; use <tt>MPI_Error_string</tt> to get more information
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about this error code.
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MPI_ERR_SIZE
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See Also
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MPI_Win_allocate MPI_Win_create MPI_Win_create_dynamic MPI_Win_free MPI_Win_shared_query
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