lock_descriptor
struct lock_descriptor *from_vertex; /* edge emanating from lock */
struct lock_descriptor *to_vertex; /* edge pointing to lock */
struct lock_descriptor *l_next; /* next active/sleep lock */
struct lock_descriptor *l_prev; /* previous active/sleep lock */
struct lock_descriptor *l_stack; /* for stack operations */
struct lock_descriptor *l_stack1; /* for stack operations */
struct lock_descriptor *l_dstack; /* stack for debug functions */
typedef struct lock_descriptor lock_descriptor_t;
struct lock_descriptor active_locks;
struct lock_descriptor sleeping_locks;