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Leetcode(Java多线程)-1114. 按序打印

热度:49   发布时间:2023-12-29 08:06:15.0

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。

方法1:volatile

class Foo {volatile int num = 0;public Foo() {}public void first(Runnable printFirst) throws InterruptedException {while(num!=0){}// printFirst.run() outputs "first". Do not change or remove this line.printFirst.run();num++;}public void second(Runnable printSecond) throws InterruptedException {while(num!=1){}// printSecond.run() outputs "second". Do not change or remove this line.printSecond.run();num++;}public void third(Runnable printThird) throws InterruptedException {while(num!=2){}// printThird.run() outputs "third". Do not change or remove this line.printThird.run();}
}

方法2:synchronize wait notifyAll

class Foo {Object lock = new Object();boolean fisrtDone = false;boolean secondDone = false;public Foo() {}public void first(Runnable printFirst) throws InterruptedException {synchronized(lock){// printFirst.run() outputs "first". Do not change or remove this line.printFirst.run();fisrtDone = true;lock.notifyAll();}}public void second(Runnable printSecond) throws InterruptedException {synchronized(lock){while(!fisrtDone){lock.wait();}// printSecond.run() outputs "second". Do not change or remove this line.printSecond.run();secondDone = true;lock.notifyAll();}}public void third(Runnable printThird) throws InterruptedException {synchronized(lock){while(!secondDone){lock.wait();}// printThird.run() outputs "third". Do not change or remove this line.        printThird.run();}}
}

思路3:AtomInteger

class Foo {private AtomicInteger firstJobDone = new AtomicInteger(0);private AtomicInteger secondJobDone = new AtomicInteger(0);public Foo() {}public void first(Runnable printFirst) throws InterruptedException {// printFirst.run() outputs "first".printFirst.run();// mark the first job as done, by increasing its count.firstJobDone.incrementAndGet();}public void second(Runnable printSecond) throws InterruptedException {while (firstJobDone.get() != 1) {// waiting for the first job to be done.}// printSecond.run() outputs "second".printSecond.run();// mark the second as done, by increasing its count.secondJobDone.incrementAndGet();}public void third(Runnable printThird) throws InterruptedException {while (secondJobDone.get() != 1) {// waiting for the second job to be done.}// printThird.run() outputs "third".printThird.run();}
}

思路4:ConutDownLatch

class Foo {CountDownLatch first = new CountDownLatch(1);CountDownLatch second = new CountDownLatch(1);public Foo() {}public void first(Runnable printFirst) throws InterruptedException {// printFirst.run() outputs "first".printFirst.run();first.countDown();}public void second(Runnable printSecond) throws InterruptedException {first.await();// printSecond.run() outputs "second".printSecond.run();second.countDown();}public void third(Runnable printThird) throws InterruptedException {second.await();// printThird.run() outputs "third".printThird.run();}
}

 

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