380. Changes from Version 2.0 to Version 2.1


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    1. Section Message Data on page Message Data , Section C++ Datatypes on page C++ Datatypes , and Annex Defined Values and Handles on page Defined Values and Handles .
    In addition, the MPI_LONG_LONG should be added as an optional type; it is a synonym for MPI_LONG_LONG_INT.


    2. Section Message Data on page Message Data , Section C++ Datatypes on page C++ Datatypes , and Annex Defined Values and Handles on page Defined Values and Handles .
    MPI_LONG_LONG_INT, MPI_LONG_LONG (as synonym), MPI_UNSIGNED_LONG_LONG, MPI_SIGNED_CHAR, and MPI_WCHAR are moved from optional to official and they are therefore defined for all three language bindings.
    3. Section Return Status on page Return Status .
    MPI_GET_COUNT with zero-length datatypes: The value returned as the count argument of MPI_GET_COUNT for a datatype of length zero where zero bytes have been transferred is zero. If the number of bytes transferred is greater than zero, MPI_UNDEFINED is returned.


    4. Section Derived Datatypes on page Derived Datatypes .
    General rule about derived datatypes: Most datatype constructors have replication count or block length arguments. Allowed values are nonnegative integers. If the value is zero, no elements are generated in the type map and there is no effect on datatype bounds or extent.


    5. Section Canonical MPI_PACK and MPI_UNPACK on page Canonical MPI_PACK and MPI_UNPACK .
    MPI_BYTE should be used to send and receive data that is packed using MPI_PACK_EXTERNAL.


    6. Section All-Reduce on page All-Reduce .
    If comm is an intercommunicator in MPI_ALLREDUCE, then both groups should provide count and datatype arguments that specify the same type signature (i.e., it is not necessary that both groups provide the same count value).
    7. Section Group Accessors on page Group Accessors .
    MPI_GROUP_TRANSLATE_RANKS and MPI_PROC_NULL: MPI_PROC_NULL is a valid rank for input to MPI_GROUP_TRANSLATE_RANKS, which returns MPI_PROC_NULL as the translated rank.


    8. Section Caching on page Caching .
    About the attribute caching functions:
    Advice to implementors.

    High-quality implementations should raise an error when a keyval that was created by a call to MPI_XXX_CREATE_KEYVAL is used with an object of the wrong type with a call to MPI_YYY_GET_ATTR, MPI_YYY_SET_ATTR, MPI_YYY_DELETE_ATTR, or MPI_YYY_FREE_KEYVAL. To do so, it is necessary to maintain, with each keyval, information on the type of the associated user function. ( End of advice to implementors.)

    9. Section Naming Objects on page Naming Objects .
    In MPI_COMM_GET_NAME: In C, a null character is additionally stored at name[resultlen]. resultlen cannot be larger then MPI_MAX_OBJECT-1. In Fortran, name is padded on the right with blank characters. resultlen cannot be larger then MPI_MAX_OBJECT.


    10. Section Overview of the Functions on page Overview of the Functions .
    About MPI_GRAPH_CREATE and MPI_CART_CREATE: All input arguments must have identical values on all processes of the group of comm_old.


    11. Section Cartesian Constructor on page Cartesian Constructor .
    In MPI_CART_CREATE: If ndims is zero then a zero-dimensional Cartesian topology is created. The call is erroneous if it specifies a grid that is larger than the group size or if ndims is negative.


    12. Section General (Graph) Constructor on page General (Graph) Constructor .
    In MPI_GRAPH_CREATE: If the graph is empty, i.e., nnodes == 0, then MPI_COMM_NULL is returned in all processes.


    13. Section General (Graph) Constructor on page General (Graph) Constructor .
    In MPI_GRAPH_CREATE: A single process is allowed to be defined multiple times in the list of neighbors of a process (i.e., there may be multiple edges between two processes). A process is also allowed to be a neighbor to itself (i.e., a self loop in the graph). The adjacency matrix is allowed to be non-symmetric.
    Advice to users.

    Performance implications of using multiple edges or a non-symmetric adjacency matrix are not defined. The definition of a node-neighbor edge does not imply a direction of the communication. ( End of advice to users.)

    14. Section Topology Inquiry Functions on page Topology Inquiry Functions .
    In MPI_CARTDIM_GET and MPI_CART_GET: If comm is associated with a zero-dimensional Cartesian topology, MPI_CARTDIM_GET returns ndims=0 and MPI_CART_GET will keep all output arguments unchanged.


    15. Section Topology Inquiry Functions on page Topology Inquiry Functions .
    In MPI_CART_RANK: If comm is associated with a zero-dimensional Cartesian topology, coord is not significant and 0 is returned in rank.


    16. Section Topology Inquiry Functions on page Topology Inquiry Functions .
    In MPI_CART_COORDS: If comm is associated with a zero-dimensional Cartesian topology, coords will be unchanged.


    17. Section Cartesian Shift Coordinates on page Cartesian Shift Coordinates .
    In MPI_CART_SHIFT: It is erroneous to call MPI_CART_SHIFT with a direction that is either negative or greater than or equal to the number of dimensions in the Cartesian communicator. This implies that it is erroneous to call MPI_CART_SHIFT with a comm that is associated with a zero-dimensional Cartesian topology.


    18. Section Partitioning of Cartesian structures on page Partitioning of Cartesian structures .
    In MPI_CART_SUB: If all entries in remain_dims are false or comm is already associated with a zero-dimensional Cartesian topology then newcomm is associated with a zero-dimensional Cartesian topology.


    19. Section Environmental Inquiries on page Environmental Inquiries .
    In MPI_GET_PROCESSOR_NAME: In C, a null character is additionally stored at name[resultlen]. resultlen cannot be larger then MPI_MAX_PROCESSOR_NAME-1. In Fortran, name is padded on the right with blank characters. resultlen cannot be larger then MPI_MAX_PROCESSOR_NAME.


    20. Section Error Handling on page Error Handling .
    MPI_{COMM,WIN,FILE}_GET_ERRHANDLER behave as if a new error handler object is created. That is, once the error handler is no longer needed, MPI_ERRHANDLER_FREE should be called with the error handler returned from MPI_ERRHANDLER_GET or MPI_{COMM,WIN,FILE}_GET_ERRHANDLER to mark the error handler for deallocation. This provides behavior similar to that of MPI_COMM_GROUP and MPI_GROUP_FREE.


    21. Section Startup on page Startup , see explanations to MPI_FINALIZE.
    MPI_FINALIZE is collective over all connected processes. If no processes were spawned, accepted or connected then this means over MPI_COMM_WORLD; otherwise it is collective over the union of all processes that have been and continue to be connected, as explained in Section Releasing Connections on page Releasing Connections .


    22. Section Startup on page Startup .
    About MPI_ABORT:
    Advice to users.

    Whether the errorcode is returned from the executable or from the MPI process startup mechanism (e.g., mpiexec), is an aspect of quality of the MPI library but not mandatory. ( End of advice to users.)

    Advice to implementors.

    Where possible, a high-quality implementation will try to return the errorcode from the MPI process startup mechanism (e.g. mpiexec or singleton init). ( End of advice to implementors.)

    23. Section The Info Object on page The Info Object .
    An implementation must support info objects as caches for arbitrary ( key, value) pairs, regardless of whether it recognizes the key. Each function that takes hints in the form of an MPI_Info must be prepared to ignore any key it does not recognize. This description of info objects does not attempt to define how a particular function should react if it recognizes a key but not the associated value. MPI_INFO_GET_NKEYS, MPI_INFO_GET_NTHKEY, MPI_INFO_GET_VALUELEN, and MPI_INFO_GET must retain all ( key, value) pairs so that layered functionality can also use the Info object.


    24. Section Communication Calls on page Communication Calls .
    MPI_PROC_NULL is a valid target rank in the MPI RMA calls MPI_ACCUMULATE, MPI_GET, and MPI_PUT. The effect is the same as for MPI_PROC_NULL in MPI point-to-point communication. See also item Changes from Version 2.0 to Version 2.1 in this list.
    25. Section Communication Calls on page Communication Calls .
    After any RMA operation with rank MPI_PROC_NULL, it is still necessary to finish the RMA epoch with the synchronization method that started the epoch. See also item Changes from Version 2.0 to Version 2.1 in this list.
    26. Section Accumulate Functions on page Accumulate Functions .
    MPI_REPLACE in MPI_ACCUMULATE, like the other predefined operations, is defined only for the predefined MPI datatypes.


    27. Section File Info on page File Info .
    About MPI_FILE_SET_VIEW and MPI_FILE_SET_INFO: When an info object that specifies a subset of valid hints is passed to MPI_FILE_SET_VIEW or MPI_FILE_SET_INFO, there will be no effect on previously set or defaulted hints that the info does not specify.


    28. Section File Info on page File Info .
    About MPI_FILE_GET_INFO: If no hint exists for the file associated with fh, a handle to a newly created info object is returned that contains no key/value pair.


    29. Section File Views on page File Views .
    If a file does not have the mode MPI_MODE_SEQUENTIAL, then MPI_DISPLACEMENT_CURRENT is invalid as disp in MPI_FILE_SET_VIEW.
    30. Section External Data Representation: ``external32'' on page External Data Representation: ``external32'' .
    The bias of 16 byte doubles was defined with 10383. The correct value is 16383.
    31. Section Class Member Functions for MPI on page Class Member Functions for MPI .
    In the example in this section, the buffer should be declared as const void* buf.
    32. Section Additional Support for Fortran Numeric Intrinsic Types on page Additional Support for Fortran Numeric Intrinsic Types .
    About MPI_TYPE_CREATE_F90_xxxx:
    Advice to implementors.

    An application may often repeat a call to MPI_TYPE_CREATE_F90_xxxx with the same combination of ( xxxx, p, r). The application is not allowed to free the returned predefined, unnamed datatype handles. To prevent the creation of a potentially huge amount of handles, the MPI implementation should return the same datatype handle for the same ( REAL/COMPLEX/INTEGER, p, r) combination. Checking for the combination ( p, r) in the preceding call to MPI_TYPE_CREATE_F90_xxxx and using a hash-table to find formerly generated handles should limit the overhead of finding a previously generated datatype with same combination of ( xxxx, p, r). ( End of advice to implementors.)

    33. Section Defined Constants on page Defined Constants .
    MPI_BOTTOM is defined as void * const MPI::BOTTOM.



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