我们提供了一个类:
- public class Foo {
- public void one() { print("one"); }
- public void two() { print("two"); }
- public void three() { print("three"); }
- }
三个不同的线程将会共用一个 Foo 实例.
线程 A 将会调用 one() 方法
线程 B 将会调用 two() 方法
线程 C 将会调用 three() 方法
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.
示例 1:
输入: [1,2,3]
输出: "onetwothree"
解释:
有三个线程会被异步启动.
输入 [1,2,3] 表示线程 A 将会调用 one() 方法, 线程 B 将会调用 two() 方法, 线程 C 将会调用 three() 方法.
正确的输出是 "onetwothree".
示例 2:
输入: [1,3,2]
输出: "onetwothree"
解释:
输入 [1,3,2] 表示线程 A 将会调用 one() 方法, 线程 B 将会调用 three() 方法, 线程 C 将会调用 two() 方法.
正确的输出是 "onetwothree".
注意:
尽管输入中的数字似乎暗示了顺序, 但是我们并不保证线程在操作系统中的调度顺序.
你看到的输入格式主要是为了确保测试的全面性.
- class Foo {
- private CountDownLatch second = new CountDownLatch(1);
- private CountDownLatch third = new CountDownLatch(1);
- public Foo() {
- }
- public void first(Runnable printFirst) throws InterruptedException {
- // printFirst.run() outputs "first". Do not change or remove this line.
- printFirst.run();
- second.countDown();
- }
- public void second(Runnable printSecond) throws InterruptedException {
- second.await();
- // printSecond.run() outputs "second". Do not change or remove this line.
- printSecond.run();
- third.countDown();
- }
- public void third(Runnable printThird) throws InterruptedException {
- third.await();
- // printThird.run() outputs "third". Do not change or remove this line.
- printThird.run();
- }
- }
- class Foo {
- private Semaphore seam_first_two = new Semaphore(0);
- private Semaphore seam_two_second = new Semaphore(0);
- public Foo() {
- }
- public void first(Runnable printFirst) throws InterruptedException {
- // printFirst.run() outputs "first". Do not change or remove this line.
- printFirst.run();
- seam_first_two.release();
- }
- public void second(Runnable printSecond) throws InterruptedException {
- seam_first_two.acquire();
- // printSecond.run() outputs "second". Do not change or remove this line.
- printSecond.run();
- seam_two_second.release();
- }
- public void third(Runnable printThird) throws InterruptedException {
- seam_two_second.acquire();
- // printThird.run() outputs "third". Do not change or remove this line.
- printThird.run();
- }
- }
来源: http://www.bubuko.com/infodetail-3400819.html