# MPI_T_pvar_read

Read the value of a performance variable

## Synopsis

    int MPI_T_pvar_read(MPI_T_pvar_session session, MPI_T_pvar_handle handle,
                        void *buf)

## Input Parameters

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

## Output Parameters

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

## Notes

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().

## Thread and Interrupt Safety

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.

## Errors

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.