# 18.2.370. MPI_T_pvar_start

MPI_T_pvar_start, MPI_T_pvar_stop - Start/stop a performance variable

## 18.2.370.1. SYNTAX

### 18.2.370.1.1. C Syntax

    #include <mpi.h>

    int MPI_T_pvar_start(MPI_T_pvar_session session, MPI_T_pvar_handle handle)

    int MPI_T_pvar_stop(MPI_T_pvar_session session, MPI_T_pvar_handle handle)

## 18.2.370.2. INPUT PARAMETERS

- `session`: Performance experiment session.

- `handle`: Performance variable handle.

## 18.2.370.3. DESCRIPTION

MPI_T_pvar_start starts the performance variable with the handle specified in handle. The special value MPI_T_PVAR_ALL_HANDLES can be passed in handle to start all non-continuous handles in the session specified in session.

MPI_T_pvar_stop stops the performance variable with the handle specified in handle. The special value MPI_T_PVAR_ALL_HANDLES can be passed in handle to stop all non-continuous handles in the session specified in session.

Continuous performance variables can neither be started nor stopped.

## 18.2.370.4. ERRORS

MPI_T_pvar_start and MPI_T_pvar_stop() will fail if:

- `MPI_T_ERR_NOT_INITIALIZED`: The MPI Tools interface not initialized

- `MPI_T_ERR_INVALID_SESSION`: Session parameter is not a valid session

- `MPI_T_ERR_INVALID_HANDLE`: Invalid handle or handle not associated with the session

- `MPI_T_ERR_PVAR_NO_STARTSTOP`: The variable cannot be started or stopped

See also

- MPI_T_pvar_get_info