/*D
   MPI_T_pvar_read - Read the value of a performance variable

Synopsis:
.vb
int MPI_T_pvar_read(MPI_T_pvar_session session, MPI_T_pvar_handle handle,
                    void *buf)
.ve

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().

.N ThreadSafe

.N Errors
.N MPI_SUCCESS
.N MPI_T_ERR_INVALID
.N MPI_T_ERR_INVALID_HANDLE
.N MPI_T_ERR_INVALID_SESSION
.N MPI_T_ERR_NOT_INITIALIZED
.N MPI_ERR_OTHER

D*/

