即使在线程终止后锁也不会释放答案

【问题标题】：Lock not released even after thread terminates即使在线程终止后锁也不会释放
【发布时间】：2018-07-23 16:18:15
【问题描述】：

在下面的程序中，不知何故程序没有结束。当我调试时，在检查lock 变量期间显示锁被生产者线程持有，如下所示

java.util.concurrent.locks.ReentrantLock@55584367[被线程锁定池 1 线程 1] java.util.concurrent.locks.ReentrantLock$NonfairSync@5b9fb7bc[状态= 8、空队列]

public class LocksTest {

    public static void main(String[] args) {
        List<String> contents = new ArrayList<>();
        Lock lock = new ReentrantLock();
        String greenColor = "\u001B[32m";
        String yellowColor = "\u001B[33m";
        String redColor = "\u001B[31m";
        MyProducer myProducer = new MyProducer(greenColor, contents, lock);
        MyConsumer myConsumer1 = new MyConsumer(yellowColor, contents, lock);
        MyConsumer myConsumer2 = new MyConsumer(redColor, contents, lock);

        ExecutorService service = Executors.newFixedThreadPool(3);
        service.execute(myProducer);
        service.execute(myConsumer2);
        service.execute(myConsumer1);
// new Thread(myProducer).start();
// new Thread(myConsumer1).start();
// new Thread(myConsumer2).start();
        service.shutdown();
    }
}

class MyProducer implements Runnable {

    private String color;
    private List<String> contents;
    private Lock lock;

    public MyProducer(String color,
                      List<String> contents,
                      Lock lock) {
        this.color = color;
        this.contents = contents;
        this.lock = lock;
    }

    @Override
    public void run() {

        int count = 0;
        while (true) {
            if (lock.tryLock()) {
                try {
                    contents.add("" + ++count);
                    System.out.println(color + "Adding " + count);
                    if (count == 5) {
                        System.out.println(color + "Adding " + "EOF");
                        contents.add("EOF");
                        break;
                    }

                    try {
                        Thread.sleep(1000l);
                    } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace();
                    }

                } finally {
                    lock.unlock();
                }
            }
        }
    }
}

class MyConsumer implements Runnable {

    private String color;
    private List<String> contents;
    private Lock lock;

    public MyConsumer(String color,
                      List<String> contents,
                      Lock lock) {
        this.color = color;
        this.contents = contents;
        this.lock = lock;
    }

    @Override
    public void run() {
        String value = null;
        while (true) {
            if (lock.tryLock()) {
                try {
                    if (!contents.isEmpty()) {
                        Iterator<String> stringItr = contents.iterator();

                        while (stringItr.hasNext())
                            value = stringItr.next();
                        System.out.println(color + "Consuming " + value);
                        stringItr.remove();
                    }
                    if ("EOF".equals(value)) {
                        break;
                    }
                } finally {
                    lock.unlock();
                }
            }
        }
    }
}

结果如下：

[32mAdding 1
[33mConsuming 1
[32mAdding 2
[33mConsuming 2
[32mAdding 3
[33mConsuming 3
[32mAdding 4
[33mConsuming 4
[32mAdding 5
[32mAdding EOF
[33mConsuming EOF
[31mConsuming 5

和

[32mAdding 1
[32mAdding 2
[32mAdding 3
[32mAdding 4
[32mAdding 5
[32mAdding EOF
[33mConsuming EOF
[31mConsuming 5
[31mConsuming 4
[31mConsuming 3
[31mConsuming 2
[31mConsuming 1

虽然结果符合预期，但我不确定程序为什么没有终止？其次，一个终止的线程可以持有lock（我观察到这种奇怪的行为是用传统的线程使用方式评论的）？！

【问题讨论】：

你有两个 while(true) 循环，但是当你解锁时你没有摆脱它们？尝试休息； lock.unlock() 之后；
您需要在工作队列中添加尽可能多的“毒丸”。
@PerryMonschau ：在那里添加一个中断会导致循环退出而不添加所有必需的项目。
@Ivan：“毒丸”是什么意思？
@Adithya dzone.com/articles/producers-and-consumers-part-3

标签： java concurrency reentrantlock

【解决方案1】：

好吧，消费者和生产者共享一个锁对我来说有点奇怪，但你的问题是生产者放置了一个 EOF 并且你有 2 个消费者。所以消费者（不是你的生产者）不能打破 while 循环。

【讨论】：