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NAME

MPI_Sendrecv - Perform a blocking send and receive of two buffers

SYNOPSIS

#include <mpi.h> int MPI_Sendrecv(void *sendbuf , int sendcount , MPI_Datatype sendtype , int dest , int sendtag , void *recvbuf , int recvcount , MPI_Datatype recvtype , int source , int recvtag , MPI_Comm comm , MPI_Status *status );

#include <pmpi.h> int PMPI_Sendrecv(void *sendbuf , int sendcount , MPI_Datatype sendtype , int dest , int sendtag , void *recvbuf , int recvcount , MPI_Datatype recvtype , int source , int recvtag , MPI_Comm comm , MPI_Status *status );

#include <mpi.h> void MPI::Comm::Sendrecv(const void *sendbuf , int sendcount , const MPI::Datatype &sendtype , int dest , int sendtag , void *recvbuf , int recvcount , const MPI::Datatype &recvtype , int source , int recvtag , MPI::Status &status ) const; void MPI::Comm::Sendrecv(const void *sendbuf , int sendcount , const MPI::Datatype &sendtype , int dest , int sendtag , void *recvbuf , int recvcount , const MPI::Datatype &recvtype , int source , int recvtag ) const;

INCLUDE 'mpif.h' MPI_SENDRECV(sendbuf , sendcount , sendtype , dest , sendtag , recvbuf , recvcount , recvtype , source , recvtag , comm , status , ierr ) <type> sendbuf (*), recvbuf (*) INTEGER sendcount , sendtype , dest , sendtag , recvcount , recvtype , source INTEGER recvtag , comm , status (MPI_STATUS_SIZE), ierr

INPUT PARAMETERS

sendbuf - send buffer (array)

sendcount - count of elements in send buffer (integer)

sendtype - type of elements in send buffer (handle)

dest - destination rank (integer)

sendtag - send communication tag (integer)

recvcount - count of elements in receive buffer (integer)

recvtype - type of elements in receive buffer (handle)

source - source rank (integer)

recvtag - receive communication tag (integer)

comm - communicator for message (handle)

OUTPUT PARAMETERS

recvbuf - receive buffer (array)

status - status of the communication (structure)

DESCRIPTION

The MPI_Sendrecv() function is used to send a message to the process with rank dest in the communicator comm , using the sendtag envelope. The send may (or may not) block depending on the amount of internal buffering done in the MPI implementation. The send consists of sendcount elements of type sendtype in an array specified by sendbuf . Simultaneously, the function also waits for a receive that matches source , recvtag , and communicator, comm , which will be copied into the buffer recvbuf . If the message is larger than the buffer, it will be truncated and the MPI_ERROR field of status will be set to MPI_ERR_TRUNCATE. The recvtype and recvcount determine exactly how the message is interpreted. Note that for performance reasons this MPI library does not check that the sent and received datatypes match.

If recvtag is MPI_ANY_TAG then any tag will match. Similarly, if source is MPI_ANY_SOURCE then so will a message from any source. The original tag and source are stored in the MPI_TAG and MPI_SOURCE fields of status respectively. One additional field, status->size holds the total size of the message in bytes.

This function is useful for communication because the internal send and receive operations can complete in any order. Individual MPI_Send() and MPI_Recv() function calls can deadlock since a receive must be posted before a blocking send can complete. The use of MPI_Sendrecv() allows simple communication patterns in rings of processes without worry of deadlock.

If the destination is MPI_PROC_NULL then no send is posted, and this function acts like a MPI_Recv(). Similarly if the source is MPI_PROC_NULL then no receive is posted, and this function acts like a MPI_Send(). In this case, status is filled with MPI_ANY_TAG MPI_PROC_NULL MPI_SUCCESS and zero size in bytes. If there is no send or receive to post, then this function will immediately return MPI_SUCCESS.

Note that the send and receive buffers should not overlap. If that is required, see the MPI_Sendrecv_replace() function.

The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Sendrecv() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_COUNT - Invalid element count;

MPI_ERR_BUFFER - Invalid buffer;

MPI_ERR_TAG - Invalid tag;

MPI_ERR_TYPE - Invalid data type;

MPI_ERR_RANK - Invalid source or destination;

MPI_ERR_INTERN - Out of memory error.

SEE ALSO

MPI_Send (3) MPI_Recv (3) MPI_Sendrecv_replace (3)

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