#include <db.h>

u_int32_t
DB_TXN->id(DB_TXN *tid);  

The DB_TXN->id() method returns the unique transaction id associated with the specified transaction. Locking calls made on behalf of this transaction should use the value returned from DB_TXN->id() as the locker parameter to the DB_ENV->lock_get() or DB_ENV->lock_vec() calls.