MPI_T_pvar_read - Read the value of a performance variable

       All  MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the
       function and Fortran routines in the last argument.  Before the value is returned, the current MPI  error
       handler  is called.  By default, this error handler aborts the MPI job.  The error handler may be changed
       with   MPI_Comm_set_errhandler   (for   communicators),   MPI_File_set_errhandler   (for   files),    and
       MPI_Win_set_errhandler  (for  RMA windows).  The MPI-1 routine MPI_Errhandler_set may be used but its use
       is deprecated.  The predefined error handler MPI_ERRORS_RETURN may be used to cause error  values  to  be
       returned.   Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI
       implementations will attempt to continue whenever possible.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.

       MPI_T_ERR_INVALID
              - Invalid use of the interface or bad parameter values(s).
       MPI_T_ERR_INVALID_HANDLE
              - The handle is invalid.
       MPI_T_ERR_INVALID_SESSION
              - Session argument is not valid.
       MPI_T_ERR_NOT_INITIALIZED
              - The MPI tool information interface is not initialized.
       MPI_ERR_OTHER
              - Other error; use MPI_Error_string to get more information about this error code.

                                                    1/21/2022                                 MPI_T_pvar_read(3)

session
              - identifier of performance experiment session (handle)
       handle - handle of a performance variable (handle)

       MPI_T_pvar_read -  Read the value of a performance variable

       The  MPI_T_pvar_read() call queries the value of the performance variable with the handle "handle" in the
       session identified by the parameter session and stores  the  result  in  the  buffer  identified  by  the
       parameter  buf.  The user is responsible to ensure that the buffer is of the appropriate size to hold the
       entire value of the performance variable (based on the datatype and count returned by  the  corresponding
       previous calls to MPI_T_pvar_get_info() and MPI_T_pvar_handle_alloc(), respectively).

       The constant MPI_T_PVAR_ALL_HANDLES cannot be used as an argument for the function MPI_T_pvar_read().

buf    - initial address of storage location for variable value (choice)

       #ifdef ENABLE_QMPI
       #ifndef MPICH_MPI_FROM_PMPI
       int QMPI_T_pvar_read(QMPI_Context context, int tool_id, MPI_T_pvar_session session,
       MPI_T_pvar_handle handle, void *buf) MPICH_API_PUBLIC

       This routine is thread-safe.  This means that this routine may be safely used by multiple threads without
       the  need  for  any  user-provided thread locks.  However, the routine is not interrupt safe.  Typically,
       this is due to the use of memory allocation routines such as malloc or other non-MPICH  runtime  routines
       that are themselves not interrupt-safe.