• 线程同步的实现方式(volatile、synchronized、CountDownLatch)


    题目:

    自定义容器,提供新增元素(add)和获取元素数量(size)方法。启动两个线程。

    线程1向容器中新增10个数据。线程2监听容器元素数量,当容器元素数量为5时,线程2输出信息并终止。

    方法一:volatile

    /**
     * volatile
     */import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.TimeUnit;
    
    public class Test_01 {
        public static void main(String[] args) {
            final Test_01_Container t = new Test_01_Container();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i < 10; i++) {
                        System.out.println("add Object to Container " + i);
                        t.add(new Object());
                        try {
                            TimeUnit.SECONDS.sleep(1);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }).start();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        if (t.size() == 5) {
                            System.out.println("size = 5");
                            break;
                        }
                    }
                }
            }).start();
        }
    }
    
    class Test_01_Container {
        volatile List<Object> container = new ArrayList<>();
    
        public void add(Object o) {
            this.container.add(o);
        }
    
        public int size() {
            return this.container.size();
        }
    }

    方法二:synchronized

    /**
     * wait notify
     */
    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.TimeUnit;
    
    public class Test_02 {
        public static void main(String[] args) {
            final Test_02_Container t = new Test_02_Container();
            final Object lock = new Object();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    synchronized (lock) {
                        if (t.size() != 5) {
                            try {
                                lock.wait(); // 线程进入等待队列。
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                        System.out.println("size = 5");
                        lock.notifyAll(); // 唤醒其他等待线程
                    }
                }
            }).start();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    synchronized (lock) {
                        for (int i = 0; i < 10; i++) {
                            System.out.println("add Object to Container " + i);
                            t.add(new Object());
                            if (t.size() == 5) {
                                lock.notifyAll();
                                try {
                                    lock.wait();
                                } catch (InterruptedException e) {
                                    e.printStackTrace();
                                }
                            }
                            try {
                                TimeUnit.SECONDS.sleep(1);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }).start();
        }
    }
    
    class Test_02_Container {
        List<Object> container = new ArrayList<>();
    
        public void add(Object o) {
            this.container.add(o);
        }
    
        public int size() {
            return this.container.size();
        }
    }

    方法三:CountDownLatch

    /**
     * CountDownLatch 门闩
     */
    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.TimeUnit;
    
    public class Test_03 {
        public static void main(String[] args) {
            final Test_03_Container t = new Test_03_Container();
            final CountDownLatch latch = new CountDownLatch(1);
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    if (t.size() != 5) {
                        try {
                            latch.await(); // 等待门闩的开放。 不是进入等待队列
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.println("size = 5");
                }
            }).start();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i < 10; i++) {
                        System.out.println("add Object to Container " + i);
                        t.add(new Object());
                        if (t.size() == 5) {
                            latch.countDown(); // 门闩-1
                        }
                        try {
                            TimeUnit.SECONDS.sleep(1);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }).start();
        }
    }
    
    class Test_03_Container {
        List<Object> container = new ArrayList<>();
    
        public void add(Object o) {
            this.container.add(o);
        }
    
        public int size() {
            return this.container.size();
        }
    }
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  • 原文地址:https://www.cnblogs.com/jing99/p/10646490.html
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