MPI_SESSION_INIT(3)

MPI_Session_init — Creates a new session handle

SYNTAX

  C Syntax

            #include <mpi.h>

            int MPI_Session_init(MPI_Info info, MPI_Errhandler errhandler, MPI_Session *session)

  Fortran Syntax

            USE MPI
            ! or the older form: INCLUDE 'mpif.h'

            MPI_SESSION_INIT(INFO, ERRHANDLER, SESSION, IERROR)
                INTEGER INFO, ERRHANDLER, SESSION, IERROR

  Fortran 2008 Syntax

            USE mpi_f08

            MPI_Session_init(info, errhandler, session, ierror)
                TYPE(MPI_Info), INTENT(IN) :: info
                TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
                TYPE(MPI_Session), INTENT(OUT) :: session
                INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

    •   info : info object (handle)

    •

        errhandler (error handler to be attached to the returned session)
            (handle)

OUTPUT PARAMETERS

    •   session : New session (handle).

    •   ierror : Fortran only: Error status (integer).

DESCRIPTION

MPI_Session_init is used to instantiate an MPI Session. The returned session handle can be used to query the runtime system about characteristics of the job within which the process is running, as well as other system resources. Other MPI communications can also be initiated in the context of an MPI session handle. All sessions must be finalized via MPI_Session_finalize <#mpi-session-finalize> before the MPI process terminates.

Multiple sessions can be created and destroyed during the lifetime of an MPI process. This is different than MPI world model, which can be initialized at most exactly once (and then subsequently finalized) during the lifetime of an MPI process.

NOTES

The info argument is used to request MPI functionality requirements and possible MPI implementation specific capabilities.

The errhandler argument specifies an error handler to invoke in the event that the Session instantiation call encounters an error.

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_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_Init <#mpi-init>

            •   MPI_Initialized <#mpi-initialized>

            •   MPI_Init_thread <#mpi-init-thread>

            •   MPI_Finalize <#mpi-finalize>

            •   MPI_Finalized <#mpi-finalized>

            •   MPI_Group_from_session_pset <#mpi-group-from-session-pset>

            •   MPI_Session_c2f <#mpi-session-c2f>

            •   MPI_Session_call_errhandler <#mpi-session-call-errhandler>

            •   MPI_Session_create_errhandler <#mpi-session-create-errhandler>

            •   MPI_Session_f2c <#mpi-session-f2c>

            •   MPI_Session_finalize <#mpi-session-finalize>

            •   MPI_Session_get_errhandler <#mpi-session-get-errhandler>

            •   MPI_Session_get_info <#mpi-session-get-info>

            •   MPI_Session_get_nth_pset <#mpi-session-get-nth-pset>

            •   MPI_Session_get_num_psets <#mpi-session-get-num-psets>

            •   MPI_Session_get_pset_info <#mpi-session-get-pset-info>

            •   MPI_Session_init

            •   MPI_Session_set_errhandler <#mpi-session-set-errhandler>

            •   MPI_T_pvar_session_create <#mpi-t-pvar-session-create>

            •   MPI_T_pvar_session_free <#mpi-t-pvar-session-free>

Copyright
2003-2026, The Open MPI Community