2019年11月15日
题目
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。
解题1：CountDownLatch
class Foo {
private CountDownLatch countDownLatchTwo = new CountDownLatch(1);
private CountDownLatch countDownLatchThree = 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();
countDownLatchTwo.countDown();
}
public void second(Runnable printSecond) throws InterruptedException {
countDownLatchTwo.await();
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
countDownLatchThree.countDown();
}
public void third(Runnable printThird) throws InterruptedException {
countDownLatchThree.await();
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}
解题2
class Foo {
private boolean firstFinished;
private boolean secondFinished;
private Object lock = new Object();
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
synchronized (lock) {
// printFirst.run() outputs "first". Do not change or remove this line.
printFirst.run();
firstFinished = true;
lock.notifyAll();
}
}
public void second(Runnable printSecond) throws InterruptedException {
synchronized (lock) {
while (!firstFinished) {
lock.wait();
}
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
secondFinished = true;
lock.notifyAll();
}
}
public void third(Runnable printThird) throws InterruptedException {
synchronized (lock) {
while (!secondFinished) {
lock.wait();
}
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}
}
