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

#include "../unipc.h"
#include "pthread_rwlock.h"
int my_phread_rwlock_tryrdlock(my_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_nwaitwriters > 0)) {
        rc = EBUSY;
    }else {
        rw->rw_refcount++;
    }
    pthread_mutex_unlock(&rw->rw_mutex);
    return rc;
}