MPI\_SESSION\_INIT(3) Open MPI MPI\_SESSION\_INIT(3) MPI\_Session\_init — Creates a new session handle # [SYNTAX](#SYNTAX) ## [C Syntax](#C_Syntax) ``` #include int MPI_Session_init(MPI_Info info, MPI_Errhandler errhandler, MPI_Session *session) ``` ## [Fortran Syntax](#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](#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](#INPUT_PARAMETERS) - **info** : info object (handle) [**errhandler (error handler to be attached to the returned session)**](#errhandler) (handle) # [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS) - **session** : New session (handle). - **ierror** : Fortran only: Error status (integer). # [DESCRIPTION](#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](#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](#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](#Copyright) 2003-2026, The Open MPI Community October 9, 2026 --- Document: MPI_Session_init(3) from openmpi-cuda-13.2 5.0.11-r1 (Chainguard OS) Source: https://github.com/open-mpi/ompi