小编use*_*036的帖子

通过这个示例信号量实现(对于SMP系统),我理解多处理器原子检查需要测试和设置.但是,一旦我们添加原子检查不是禁用中断冗余？无论如何,禁用中断仅在一个处理器上提供原子性.除了信号量队列之外,还需要加以保护.

class semaphore {
private int t;
private int count;
private queue q;

public semaphore(int init)
{
    t = 0;
    count = init;
    q = new queue();
}

public void P()
{
    Disable interrupts;
    while (TAS(t) != 0) { /* just spin */ };
    if (count > 0) {
        count--;
        t = 0;
        Enable interrupts;
        return;
    }
    Add process to q;
    t = 0;
    Enable interrupts;
    Redispatch;
}

public V()
{
    Disable interrupts;
    while (TAS(t) != 0) { /* just …