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

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

int my_pthread_rwlock_trywrlock(pthread_rwlock_t *rw)
{
    int rc;

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

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

    if(rw->rw_refcount != 0) {
        rc = EBUSY;
    }else {
        rw->rw_refcount = -1;
    }
    pthread_mutex_unlock(&rw->rw_mutex);
    return rc;
}