typedef struct data_source data_source;

typedef struct queue queue;

/**
 * Returns:
 *  0 - on success
 * -1 - on data source failure
 * -2 - on queue overflow
 */
int get_data(data_source *ds, queue *queue);

/**
 * Returns:
 *  0 - on success
 * -1 - on error and error_code is set to
 *      1 - if queue overflow occurs
 *      2 - if data source failure detected
 */
int get_data(data_source *ds, queue *queue, int *error_code);