MPI_Recv(3)                        Open MPI                        MPI_Recv(3)



NAME
       MPI_Recv - Performs a standard-mode blocking receive.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
            int source, int tag, MPI_Comm comm, MPI_Status *status)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_RECV(BUF, COUNT, DATATYPE, SOURCE, TAG, COMM, STATUS, IERROR)
            <type>    BUF(*)
            INTEGER   COUNT, DATATYPE, SOURCE, TAG, COMM
            INTEGER   STATUS(MPI_STATUS_SIZE), IERROR


C++ Syntax
       #include <mpi.h>
       void Comm::Recv(void* buf, int count, const Datatype& datatype,
            int source, int tag, Status& status) const

       void Comm::Recv(void* buf, int count, const Datatype& datatype,
            int source, int tag) const


INPUT PARAMETERS
       count     Maximum number of elements to receive (integer).

       datatype  Datatype of each receive buffer entry (handle).

       source    Rank of source (integer).

       tag       Message tag (integer).

       comm      Communicator (handle).


OUTPUT PARAMETERS
       buf       Initial address of receive buffer (choice).

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       This basic receive operation, MPI_Recv, is blocking: it returns only
       after the receive buffer contains the newly received message. A receive
       can complete before the matching send has completed (of course, it can
       complete only after the matching send has started).

       The blocking semantics of this call are described in Section 3.4 of the
       MPI-1 Standard, "Communication Modes."

       The receive buffer contains a number (defined by the value of count) of
       consecutive elements. The first element in the set of elements is
       located at address_buf. The type of each of these elements is specified
       by datatype.

       The length of the received message must be less than or equal to the
       length of the receive buffer. An  MPI_ERR_TRUNCATE is returned upon the
       overflow condition.

       If a message that is shorter than the length of the receive buffer
       arrives, then only those locations corresponding to the (shorter)
       received message are modified.


NOTES
       The count argument indicates the maximum number of entries of type
       datatype that can be received in a message. Once a message is received,
       use the MPI_Get_count function to determine the actual number of
       entries within that message.

       To receive messages of unknown length, use the MPI_Probe function. (For
       more information about MPI_Probe and MPI_Cancel, see their respective
       man pages; also, see Section 3.8 of the MPI-1 Standard, "Probe and
       Cancel.")

       A message can be received by a receive operation only if it is
       addressed to the receiving process, and if its source, tag, and
       communicator (comm) values match the source, tag, and comm values
       specified by the receive operation. The receive operation may specify a
       wildcard value for source and/or tag, indicating that any source and/or
       tag are acceptable. The wildcard value for source is source =
       MPI_ANY_SOURCE. The wildcard value for tag is tag = MPI_ANY_TAG. There
       is no wildcard value for comm. The scope of these wildcards is limited
       to the proceses in the group of the specified communicator.

       The message tag is specified by the tag argument of the receive
       operation.

       The argument source, if different from MPI_ANY_SOURCE, is specified as
       a rank within the process group associated with that same communicator
       (remote process group, for intercommunicators). Thus, the range of
       valid values for the source argument is {0,...,n-1} {MPI_ANY_SOURCE},
       where n is the number of processes in this group.

       Note the asymmetry between send and receive operations: A receive
       operation may accept messages from an arbitrary sender; on the other
       hand, a send operation must specify a unique receiver. This matches a
       "push" communication mechanism, where data transfer is effected by the
       sender (rather than a "pull" mechanism, where data transfer is effected
       by the receiver).

       Source = destination is allowed, that is, a process can send a message
       to itself. However, it is not recommended for a process to send
       messages to itself using the blocking send and receive operations
       described above, since this may lead to deadlock. See Section 3.5 of
       the MPI-1 Standard, "Semantics of Point-to-Point Communication."

       If your application does not need to examine the status field, you can
       save resources by using the predefined constant MPI_STATUS_IGNORE as a
       special value for the status argument.


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.


SEE ALSO
       MPI_Irecv
       MPI_Probe






1.4.1                            Jan 14, 2010                      MPI_Recv(3)
