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

#include "../unipc.h"
#include "pthread_rwlock.h"
void rwlock_cancelwrwait(void *arg)
{
    int rc;
    my_pthread_rwlock_t * rw;

    rw = (my_pthread_rwlock_t *)arg;

    rw->rw_nwaitwriters--;
    rc = pthread_mutex_unlock(&rw->rw_mutex);
}

int my_pthread_rwlock_wrlock(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;

    while(rw->rw_refcount != 0) {
        rw->rw_nwaitwriters++;
        pthread_cleanup_push(rwlock_cancelwrwait,(void*)rw);
        rc = pthread_cond_wait(&rw->rw_condwriters,&rw->rw_mutex);
        pthread_cleanup_pop(0);
        rw->rw_nwaitwriters--;
        if(rc != 0)
            break;
    }
    rw->rw_refcount = -1;
    pthread_mutex_unlock(&rw->rw_mutex);
    return rc;
}