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我得到了一個讀/寫鎖的實現，如下所示。請注意，在功能開始時，有一個pthread_mutex_lock呼叫。如果無論如何都使用pthread_mutex_lock，那麼使用讀/寫鎖有什麼好處。如何比簡單地使用pthread_mutex_lock好？爲什麼讀/寫鎖需要鎖？
int pthread_rwlock_rlock_np(pthread_rwlock_t *rwlock)
{
pthread_mutex_lock(&(rwlock->mutex));
rwlock->r_waiting++;
while (rwlock->r_wait > 0)
{
pthread_cond_wait(&(rwlock->r_ok), &(rwlock->mutex));
}
rwlock->reading++;
rwlock->r_waiting--;
pthread_mutex_unlock(&(rwlock->mutex));
return 0;
}
int pthread_rwlock_wlock_np(pthread_rwlock_t *rwlock)
{
pthread_mutex_lock(&(rwlock->mutex));
if(pthread_mutex_trylock(&(rwlock->w_lock)) == 0)
{
rwlock->r_wait = 1;
rwlock->w_waiting++;
while (rwlock->reading > 0)
{
pthread_cond_wait(&(rwlock->w_ok), &(rwlock->mutex));
}
rwlock->w_waiting--;
pthread_mutex_unlock(&(rwlock->mutex));
return 0;
}
else
{
rwlock->wu_waiting++;
while (pthread_mutex_trylock(&(rwlock->w_lock)) != 0)
{
pthread_cond_wait(&(rwlock->w_unlock), &(rwlock->mutex));
}
rwlock->wu_waiting--;
rwlock->r_wait = 1;
rwlock->w_waiting++;
while (rwlock->reading > 0)
{
pthread_cond_wait(&(rwlock->w_ok), &(rwlock->mutex));
}
rwlock->w_waiting--;
pthread_mutex_unlock(&(rwlock->mutex));
return 0;
}
}