实现一个锁(Implementing a lock)

 我试图了解锁的工作原理。 
 
 假设我想在C ++中实现一个非常简单的锁 
 
class Resource{
    public:
    bool lock();
    void unlock();
    ... methods to change/read the Resource ...

    private:
    bool isLocked;
}
 
 Resource的用户调用lock() ，并且如果isLocked为true，则lock()返回false，并且Resource的用户必须等待或执行其他操作。 如果isLocked为false，则lock()将isLocked设置为true，并返回true。 然后，调用者可以做任何他想要的资源。 之后他在资源上调用unlock()将isLocked设置为false。 
 
 但是，如果资源的两个用户恰好同时调用lock()会怎么样？ 这种情况很少发生吗？ 我认为更正式的，这涉及到使lock()操作“原子”，尽管我不能确切地确定这个词的含义。 

I'm trying to understand how locks work.
 
Let's say I want to implement a really simple lock in C++
 
class Resource{
    public:
    bool lock();
    void unlock();
    ... methods to change/read the Resource ...

    private:
    bool isLocked;
}
 
The user of the Resource calls lock(), and if isLocked is true, then lock() returns false, and the user of the Resource has to either wait, or do something else. If isLocked is false, then lock() sets isLocked to true, and returns true. Then the caller can do whatever he wants to the resource. He calls unlock() on the resource afterwards to set isLocked to false.
 
However, what if two users of the resource call lock() at precisely the same time? Does this situation rarely happen? I think more formally, this involves making the lock() operation "atomic", though I'm not precisely sure what that word means.

原文：https://stackoverflow.com/questions/10058747