信号量可以只用锁来制作吗？
我想知道是否可以仅使用锁来构建信号量。我见过使用中断禁用/启用以及使用原子原语（如测试和设置）的实现，但是是否可以仅使用锁来实现？
似乎做类似的事情
guard = 0;
...
while(test&set(guard));
基本上与做 lock.acquire() 相同。我在这里错过了什么吗？
编辑：我问这个问题的部分原因是因为我在这里阅读这些幻灯片：http://www.cs.washington.edu/homes/arvind/cs422/lectureNotes/l7-6.pdf 这些幻灯片提供了以下实现使用中断禁用和测试和设置的信号量，但提出了使用锁的信号量的实现作为一个问题，我认为这意味着使用锁的实现可能由于某种原因而不起作用。
I was wondering if a semaphore can be built using just locks. I've seen implementations with interrupt disable/enable and using atomic primitives like test&set, but is it possible to implement one using locks only?
It seems like doing something like
guard = 0;
...
while(test&set(guard));
is basically the same as doing a lock.acquire(). Am I missing anything here?
Edit: Part of the reason I'm asking this question is because I was reading these slides here: http://www.cs.washington.edu/homes/arvind/cs422/lectureNotes/l7-6.pdf These slides offer implementations of semaphores using interrupt disable and test&set, but poses the implementation of semaphores using locks as a question, which I took to imply that an implementation using locks might not work for some reason.
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我认为问题在于你在那个循环中忙着等待。您所说的 acquire() 是一个进入睡眠状态的操作，只有在获取信号量后才会被唤醒。
I think the problem is that you're busy-waiting in that loop. What you call acquire() would be an operation that goes to sleep and is only woken up once the the semaphore has been acquired.