多线程 – 信号量P和V操作是否为原子？

可以在信号量上执行的P()和V()操作是否保证原子？信号量可以防止两个进程进入P()？

解决方法

取自我的大学笔记：

We can think if P and V as controlling
access to a resource:

When a process wants to use the
resource,it performs a P operation:
if this succeeds,it decrements the
amount of resource available and the
process continues; if all the
resource is currently in use,the
process has to wait.

When a process is finished with the
resource,it performs a V operation:
if there were processes waiting on the
resource,one of these is woken up;
if there were no waiting processes,
the semaphore is incremented
indicating that there is now more of
the resource free. Note that the
definition of V doesn’t specify which
process is woken up if more than one
process has been suspended on the same
semaphore.

信号量可以解决互斥和条件同步问题.所以你的问题的答案是：是的.

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