Leetcode 的多线程编程真好玩，提交多几次就过了，薛定谔的 AC

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我觉得代码没问题，可能是他判题的机制需要改善一下，不能光看打印啊。。

题目：请设计修改程序，以确保 two() 方法在 one() 方法之后被执行，three() 方法在 two() 方法之后被执行。

https://leetcode-cn.com/problems/print-in-order/

这个代码可能提交 10 次会有一次通过 [滑稽]

import java.util.concurrent.atomic.AtomicInteger;

class Foo {

    public Foo() {

    }

    private AtomicInteger counter = new AtomicInteger(0);
    
    public void first(Runnable printFirst) throws InterruptedException {
        while (!counter.compareAndSet(0, 1)) ;
        printFirst.run();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        while (!counter.compareAndSet(1, 2));
        printSecond.run();
    }

    public void third(Runnable printThird) throws InterruptedException {
        while (!counter.compareAndSet(2, 3));
        printThird.run();
    }
}

1 replies

lhx2008

Jul 28, 2019

想了一下可能确实是我的问题，要 CAS 包起来就没问题了

import java.util.concurrent.atomic.AtomicInteger;

class Foo {

public Foo() {

}

private AtomicInteger counter = new AtomicInteger(0);

public void first(Runnable printFirst) throws InterruptedException {
while (!counter.compareAndSet(0, 1)) ;
printFirst.run();
while (!counter.compareAndSet(1, 2)) ;
}

public void second(Runnable printSecond) throws InterruptedException {
while (!counter.compareAndSet(2, 3));
printSecond.run();
while (!counter.compareAndSet(3, 4)) ;

}

public void third(Runnable printThird) throws InterruptedException {
while (!counter.compareAndSet(4, 5));
printThird.run();
while (!counter.compareAndSet(5, 6));
}
}