How to design sequence lock API

#include "seqlock.h"
typedef struct {
    unsigned seq;
    pthread_mutex_t lock;
} seqlock_t;
int pthread_seqlock_init(pthread_seqlock_t *seqlock);
int pthread_rwlock_destroy(pthread_seqlock_t *seqlock);

I try to understand sequence lock but sequence lock API to new for me