326 lines
12 KiB
Groff
326 lines
12 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_ALLTOALLW" "3" "Feb 14, 2025" "" "Open MPI"
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.sp
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\fI\%MPI_Alltoallw\fP, \fI\%MPI_Ialltoallw\fP, \fI\%MPI_Alltoallw_init\fP \- All processes
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send data of different types to, and receive data of different types
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from, all processes
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.SH SYNTAX
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.SS C Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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#include <mpi.h>
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int MPI_Alltoallw(const void *sendbuf, const int sendcounts[],
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const int sdispls[], const MPI_Datatype sendtypes[],
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void *recvbuf, const int recvcounts[], const int rdispls[],
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const MPI_Datatype recvtypes[], MPI_Comm comm)
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int MPI_Ialltoallw(const void *sendbuf, const int sendcounts[],
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const int sdispls[], const MPI_Datatype sendtypes[],
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void *recvbuf, const int recvcounts[], const int rdispls[],
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const MPI_Datatype recvtypes[], MPI_Comm comm,
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MPI_Request *request)
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int MPI_Alltoallw_init(const void *sendbuf, const int sendcounts[],
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const int sdispls[], const MPI_Datatype sendtypes[],
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void *recvbuf, const int recvcounts[], const int rdispls[],
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const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Info info,
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MPI_Request *request)
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE MPI
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! or the older form: INCLUDE \(aqmpif.h\(aq
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MPI_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
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RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
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INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
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INTEGER COMM, IERROR
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MPI_IALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
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RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
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INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
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INTEGER COMM, REQUEST, IERROR
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MPI_ALLTOALLW_INIT(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
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RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, INFO, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
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INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
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INTEGER COMM, INFO, REQUEST, IERROR
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran 2008 Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE mpi_f08
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MPI_Alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf, recvcounts,
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rdispls, recvtypes, comm, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
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TYPE(*), DIMENSION(..) :: recvbuf
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INTEGER, INTENT(IN) :: sendcounts(*), sdispls(*), recvcounts(*),
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rdispls(*)
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TYPE(MPI_Datatype), INTENT(IN) :: sendtypes(*)
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TYPE(MPI_Datatype), INTENT(IN) :: recvtypes(*)
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TYPE(MPI_Comm), INTENT(IN) :: comm
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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MPI_Ialltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
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recvcounts, rdispls, recvtypes, comm, request, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
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TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
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INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
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recvcounts(*), rdispls(*)
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TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
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recvtypes(*)
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TYPE(MPI_Comm), INTENT(IN) :: comm
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TYPE(MPI_Request), INTENT(OUT) :: request
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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MPI_Alltoallw_init(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
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recvcounts, rdispls, recvtypes, comm, fIinfo, request, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
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TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
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INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
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recvcounts(*), rdispls(*)
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TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
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recvtypes(*)
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TYPE(MPI_Comm), INTENT(IN) :: comm
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TYPE(MPI_Info), INTENT(IN) :: info
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TYPE(MPI_Request), INTENT(OUT) :: request
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH INPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBsendbuf\fP: Starting address of send buffer.
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.IP \(bu 2
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\fBsendcounts\fP: Integer array, where entry i specifies the number of elements to send to rank i.
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.IP \(bu 2
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\fBsdispls\fP: Integer array, where entry i specifies the displacement (in bytes, offset from \fIsendbuf) from which to send data to rank i.\fP
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.IP \(bu 2
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\fBsendtypes\fP: Datatype array, where entry i specifies the datatype to use when sending data to rank i.
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.IP \(bu 2
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\fBrecvcounts\fP: Integer array, where entry j specifies the number of elements to receive from rank j.
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.IP \(bu 2
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\fBrdispls\fP: Integer array, where entry j specifies the displacement (in bytes, offset from \fIrecvbuf) to which data from rank j should\fP be written.
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.IP \(bu 2
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\fBrecvtypes\fP: Datatype array, where entry j specifies the datatype to use when receiving data from rank j.
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.IP \(bu 2
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\fBcomm\fP: Communicator over which data is to be exchanged.
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.IP \(bu 2
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\fBinfo\fP: Info (handle, persistent only)
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.UNINDENT
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.SH OUTPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBrecvbuf\fP: Address of receive buffer.
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.IP \(bu 2
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\fBrequest\fP: Request (handle, non\-blocking only).
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.IP \(bu 2
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\fBierror\fP: Fortran only: Error status.
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.UNINDENT
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.SH DESCRIPTION
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.sp
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\fI\%MPI_Alltoallw\fP is a generalized collective operation in which all
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processes send data to and receive data from all other processes. It
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adds flexibility to \fI\%MPI_Alltoallv\fP by allowing the user to specify the
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datatype of individual data blocks (in addition to displacement and
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element count). Its operation can be thought of in the following way,
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where each process performs 2n (n being the number of processes in
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communicator \fIcomm) independent point\-to\-point communications\fP
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(including communication with itself).
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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MPI_Comm_size(comm, &n);
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for (i = 0, i < n; i++)
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MPI_Send(sendbuf + sdispls[i], sendcounts[i],
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sendtypes[i], i, ..., comm);
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for (i = 0, i < n; i++)
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MPI_Recv(recvbuf + rdispls[i], recvcounts[i],
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recvtypes[i], i, ..., comm);
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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Process j sends the k\-th block of its local \fIsendbuf to process\fP k,
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which places the data in the j\-th block of its local \fIrecvbuf.\fP
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.sp
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When a pair of processes exchanges data, each may pass different element
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count and datatype arguments so long as the sender specifies the same
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amount of data to send (in bytes) as the receiver expects to receive.
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.sp
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Note that process i may send a different amount of data to process j
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than it receives from process j. Also, a process may send entirely
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different amounts and types of data to different processes in the
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communicator.
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.sp
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WHEN COMMUNICATOR IS AN INTER\-COMMUNICATOR
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.sp
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When the communicator is an inter\-communicator, the gather operation
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occurs in two phases. The data is gathered from all the members of the
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first group and received by all the members of the second group. Then
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the data is gathered from all the members of the second group and
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received by all the members of the first. The operation exhibits a
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symmetric, full\-duplex behavior.
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.sp
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The first group defines the root process. The root process uses MPI_ROOT
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as the value of \fIroot\fP\&. All other processes in the first group use
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\fBMPI_PROC_NULL\fP as the value of \fIroot\fP\&. All processes in the second group
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use the rank of the root process in the first group as the value of
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\fIroot\fP\&.
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.sp
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When the communicator is an intra\-communicator, these groups are the
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same, and the operation occurs in a single phase.
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.SH USE OF IN-PLACE OPTION
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.sp
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When the communicator is an intracommunicator, you can perform an
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all\-to\-all operation in\-place (the output buffer is used as the input
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buffer). Use the variable MPI_IN_PLACE as the value of \fIsendbuf\fP\&. In
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this case, \fIsendcounts\fP, \fIsdispls\fP, and \fIsendtypes\fP are ignored. The
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input data of each process is assumed to be in the area where that
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process would receive its own contribution to the receive buffer.
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.SH NOTES
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.sp
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The specification of counts, types, and displacements should not cause
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any location to be written more than once.
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.sp
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All arguments on all processes are significant. The \fIcomm\fP argument, in
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particular, must describe the same communicator on all processes.
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.sp
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The offsets of \fIsdispls\fP and \fIrdispls\fP are measured in bytes. Compare
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this to \fI\%MPI_Alltoallv\fP, where these offsets are measured in units of
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\fIsendtype\fP and \fIrecvtype\fP, respectively.
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.SH ERRORS
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.sp
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Almost all MPI routines return an error value; C routines as the return result
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of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler associated
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with the communication object (e.g., communicator, window, file) is called.
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If no communication object is associated with the MPI call, then the call is
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considered attached to MPI_COMM_SELF and will call the associated MPI error
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handler. When MPI_COMM_SELF is not initialized (i.e., before
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\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
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Model exclusively) the error raises the initial error handler. The initial
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error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
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MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
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argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
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error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
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handler is called for all other MPI functions.
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.sp
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Open MPI includes three predefined error handlers that can be used:
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.INDENT 0.0
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.IP \(bu 2
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\fBMPI_ERRORS_ARE_FATAL\fP
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Causes the program to abort all connected MPI processes.
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.IP \(bu 2
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\fBMPI_ERRORS_ABORT\fP
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An error handler that can be invoked on a communicator,
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window, file, or session. When called on a communicator, it
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acts as if \fI\%MPI_Abort\fP was called on that communicator. If
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called on a window or file, acts as if \fI\%MPI_Abort\fP was called
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on a communicator containing the group of processes in the
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corresponding window or file. If called on a session,
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aborts only the local process.
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.IP \(bu 2
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\fBMPI_ERRORS_RETURN\fP
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Returns an error code to the application.
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.UNINDENT
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.sp
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MPI applications can also implement their own error handlers by calling:
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
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.IP \(bu 2
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\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.UNINDENT
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.sp
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Note that MPI does not guarantee that an MPI program can continue past
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an error.
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.sp
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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.sp
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See the Error Handling section of the MPI\-3.1 standard for
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more information.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Alltoall\fP
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.IP \(bu 2
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\fI\%MPI_Alltoallv\fP
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.UNINDENT
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.UNINDENT
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.UNINDENT
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.SH COPYRIGHT
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2003-2025, The Open MPI Community
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.\" Generated by docutils manpage writer.
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.
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