互斥锁与条件变量实现读写锁----my_pthread_rwlock_unlock

#include "../unipc.h"
#include "pthread_rwlock.h"


int my_pthread_rwlock_unlock(pthread_rwlock_t *rw)
{
    int rc;

    if(rw->rw_magic != RW_MAGIC)
        return EINVAL;

    rc = pthread_mutex_lock(&rw->rw_mutex);
    if(rc != 0)
        return rc;


    if(rw->rw_refcount == -1) {
        rw->rw_refcount = 0;
    }else {
        rw->rw_refcount--;
    }
    /*write's priority is higher than read's priority,prevent continue read will let write wait forever*/
    if(rw->rw_nwaitwriters > 0) {
     /*if the lock is write, then refcount is zero, if the lock is read, maybe refcount is > zero.send cond_signal when all lock is free*/
        if(rw->rw_refcount == 0)
            rc = pthread_cond_signal(&rw->rw_condwriters);
    }else if(rw->rw_nwaitreaders > 0) { /*no writers waits */
        rc = pthread_cond_broadcast(&rw->rw_condreaders);
    }


    pthread_mutex_unlock(&rw->rw_mutex);

    return rc;
}