MPI\_ALLGATHERV(3) Open MPI MPI\_ALLGATHERV(3) MPI\_Allgatherv, MPI\_Iallgatherv <#mpi-iallgatherv>, MPI\_Allgatherv\_init <#mpi-allgatherv-init> - Gathers data from all processes and delivers it to all. Each process may contribute a different amount of data. # [SYNTAX](#SYNTAX) ## [C Syntax](#C_Syntax) ``` #include int MPI_Allgatherv(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, const int recvcounts[], const int displs[], MPI_Datatype recvtype, MPI_Comm comm) int MPI_Iallgatherv(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, const int recvcounts[], const int displs[], MPI_Datatype recvtype, MPI_Comm comm, MPI_Request *request) int MPI_Allgatherv_init(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, const int recvcounts[], const int displs[], MPI_Datatype recvtype, MPI_Comm comm, MPI_Info info, MPI_Request *request) ``` ## [Fortran Syntax](#Fortran_Syntax) ``` USE MPI ! or the older form: INCLUDE 'mpif.h' MPI_ALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, DISPLS, RECVTYPE, COMM, IERROR) SENDBUF(*), RECVBUF(*) INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*) INTEGER DISPLS(*), RECVTYPE, COMM, IERROR MPI_IALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, DISPLS, RECVTYPE, COMM, REQUEST, IERROR) SENDBUF(*), RECVBUF(*) INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*), INTEGER DISPLS(*), RECVTYPE, COMM, REQUEST, IERROR MPI_ALLGATHERV_INIT(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, DISPLS, RECVTYPE, COMM, INFO, REQUEST, IERROR) SENDBUF(*), RECVBUF(*) INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*), INTEGER DISPLS(*), RECVTYPE, COMM, INFO, REQUEST, IERROR ``` ## [Fortran 2008 Syntax](#Fortran_2008_Syntax) ``` USE mpi_f08 MPI_Allgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs, recvtype, comm, ierror) TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf TYPE(*), DIMENSION(..) :: recvbuf INTEGER, INTENT(IN) :: sendcount, recvcounts(*), displs(*) TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype TYPE(MPI_Comm), INTENT(IN) :: comm INTEGER, OPTIONAL, INTENT(OUT) :: ierror MPI_Iallgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs, recvtype, comm, request, ierror) TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf INTEGER, INTENT(IN) :: sendcount INTEGER, INTENT(IN), ASYNCHRONOUS :: recvcounts(*), displs(*) TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype TYPE(MPI_Comm), INTENT(IN) :: comm TYPE(MPI_Request), INTENT(OUT) :: request INTEGER, OPTIONAL, INTENT(OUT) :: ierror MPI_Allgatherv_init(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs, recvtype, comm, info, request, ierror) TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf INTEGER, INTENT(IN) :: sendcount INTEGER, INTENT(IN), ASYNCHRONOUS :: recvcounts(*), displs(*) TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype TYPE(MPI_Comm), INTENT(IN) :: comm TYPE(MPI_Info), INTENT(IN) :: info TYPE(MPI_Request), INTENT(OUT) :: request INTEGER, OPTIONAL, INTENT(OUT) :: ierror ``` # [INPUT PARAMETERS](#INPUT_PARAMETERS) - **sendbuf**: Starting address of send buffer (choice). - **sendcount**: Number of elements in send buffer (integer). - **sendtype**: Datatype of send buffer elements (handle). - **recvcount**: Integer array (of length group size) containing the number of elements that are received from each process. - **displs**: Integer array (of length group size). Entry i specifies the displacement (relative to recvbuf) at which to place the incoming data from process i. - **recvtype**: Datatype of receive buffer elements (handle). - **comm**: Communicator (handle). - **info**: Info (handle, persistent only). # [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS) - **recvbuf**: Address of receive buffer (choice). - **request**: Request (handle, non-blocking only). - **ierror**: Fortran only: Error status (integer). # [DESCRIPTION](#DESCRIPTION) MPI\_Allgatherv is similar to MPI\_Allgather <#mpi-allgather> in that all processes gather data from all other processes, except that each process can send a different amount of data. The block of data sent from the jth process is received by every process and placed in the jth block of the buffer *recvbuf.* The type signature associated with sendcount, sendtype, at process j must be equal to the type signature associated with recvcounts\[j], recvtype at any other process. The outcome is as if all processes executed calls to ``` MPI_Allgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcount, displs,recvtype,root,comm); // for root = 0 , ..., n-1. ``` The rules for correct usage of MPI\_Allgatherv are easily found from the corresponding rules for MPI\_Gatherv <#mpi-gatherv>. # [USE OF IN-PLACE OPTION](#USE_OF_IN-PLACE_OPTION) When the communicator is an intracommunicator, you can perform an all-gather operation in-place (the output buffer is used as the input buffer). Use the variable MPI\_IN\_PLACE as the value of *sendbuf*. In this case, *sendcount* and *sendtype* are ignored. The input data of each process is assumed to be in the area where that process would receive its own contribution to the receive buffer. Specifically, the outcome of a call to MPI\_Allgatherv that used the in-place option is identical to the case in which all processes executed *n* calls to ``` MPI_Allgatherv ( MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, recvbuf, recvcounts, displs, recvtype, root, comm ); // for root =0, ... , n-1. ``` Note that MPI\_IN\_PLACE is a special kind of value; it has the same restrictions on its use as MPI\_BOTTOM. Because the in-place option converts the receive buffer into a send-and-receive buffer, a Fortran binding that includes INTENT must mark these as INOUT, not OUT. # [WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR](#WHEN_COMMUNICATOR_IS_AN_INTER-COMMUNICATOR) When the communicator is an inter-communicator, the gather operation occurs in two phases. The data is gathered from all the members of the first group, concatenated, and received by all the members of the second group. Then the data is gathered from all the members of the second group, concatenated, and received by all the members of the first. The send buffer arguments in the one group must be consistent with the receive buffer arguments in the other group, and vice versa. The operation must exhibit symmetric, full-duplex behavior. # [ERRORS](#ERRORS) Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument. Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI\_COMM\_SELF and will call the associated MPI error handler. When MPI\_COMM\_SELF is not initialized (i.e., before MPI\_Init <#mpi-init>/MPI\_Init\_thread <#mpi-init-thread>, after MPI\_Finalize <#mpi-finalize>, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI\_Comm\_set\_errhandler <#mpi-comm-set-errhandler> on MPI\_COMM\_SELF when using the World model, or the mpi\_initial\_errhandler CLI argument to mpiexec or info key to MPI\_Comm\_spawn <#mpi-comm-spawn>/MPI\_Comm\_spawn\_multiple <#mpi-comm-spawn-multiple>. If no other appropriate error handler has been set, then the MPI\_ERRORS\_RETURN error handler is called for MPI I/O functions and the MPI\_ERRORS\_ABORT error handler is called for all other MPI functions. Open MPI includes three predefined error handlers that can be used: - **MPI\_ERRORS\_ARE\_FATAL** Causes the program to abort all connected MPI processes. - **MPI\_ERRORS\_ABORT** An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI\_Abort <#mpi-abort> was called on that communicator. If called on a window or file, acts as if MPI\_Abort <#mpi-abort> was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process. - **MPI\_ERRORS\_RETURN** Returns an error code to the application. MPI applications can also implement their own error handlers by calling: - MPI\_Comm\_create\_errhandler <#mpi-comm-create-errhandler> then MPI\_Comm\_set\_errhandler <#mpi-comm-set-errhandler> - MPI\_File\_create\_errhandler <#mpi-file-create-errhandler> then MPI\_File\_set\_errhandler <#mpi-file-set-errhandler> - MPI\_Session\_create\_errhandler <#mpi-session-create-errhandler> then MPI\_Session\_set\_errhandler <#mpi-session-set-errhandler> or at MPI\_Session\_init <#mpi-session-init> - MPI\_Win\_create\_errhandler <#mpi-win-create-errhandler> then MPI\_Win\_set\_errhandler <#mpi-win-set-errhandler> Note that MPI does not guarantee that an MPI program can continue past an error. See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>. See the Error Handling section of the MPI-3.1 standard for more information. **See also:** - MPI\_Gatherv <#mpi-gatherv> - MPI\_Allgather <#mpi-allgather> # [Copyright](#Copyright) 2003-2026, The Open MPI Community October 26, 2026 --- Document: MPI_Allgatherv(3) from openmpi-cuda-13.3 5.0.11-r1 (Chainguard OS) Source: https://github.com/open-mpi/ompi