java 多线程实现生产者模型问题

Question

你的代码没有问题，我重新组织了一下，以便更好地观察结果。import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;/**
 * 多线程生产者-消费者示例
 */
public class Basket {    public static final int BASKET_CAPACITY = 5;    private List<String> list = new ArrayList<>();    private Lock lock = new ReentrantLock();    private Condition setter = lock.newCondition(); //篮子为满的条件    private Condition getter = lock.newCondition(); //篮子为空的条件    // 放入苹果
    public void addApple() throws InterruptedException {
        try {
            lock.lock();
            while (list.size() >= BASKET_CAPACITY) {
                outputThreadMessage("篮子已满，等待取出", false);
                setter.await();
            }
            list.add("红富士");
            outputThreadMessage("放入苹果: 篮子里还有" + list.size(), false);            getter.signalAll();
        } finally {
            lock.unlock();
        }
    }    // 取出苹果
    public void removeApple() throws InterruptedException {
        try {
            lock.lock();
            while (list.size() <= 0) {
                outputThreadMessage("篮子已空，等待放入", true);
                getter.await();
            }
            list.remove(0);
            outputThreadMessage("取出苹果: 篮子里还有" + list.size(), true);            setter.signalAll();
        } finally {
            lock.unlock();
        }
    }    public static void main(String[] args) {
        final Basket baskert = new Basket();        // 通过调整 AddAppleTask 和 RemoveAppleTask 的线程数，可以
        // 观察篮子满或空的情况
        
        new Thread(new AddAppleTask(baskert)).start();
        new Thread(new AddAppleTask(baskert)).start();        new Thread(new RemoveAppleTask(baskert)).start();
        new Thread(new RemoveAppleTask(baskert)).start();
    }    /**
     * 放入苹果线程
     */
    private static class AddAppleTask implements Runnable {        private final Basket basket;        public AddAppleTask(Basket basket) {
            this.basket = basket;
        }        public void run() {
            try {
                while (waitRandomTime()) {
                    basket.addApple();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }    }    /**
     * 取出苹果线程
     */
    private static class RemoveAppleTask implements Runnable {        private final Basket basket;        public RemoveAppleTask(Basket basket) {
            this.basket = basket;
        }        public void run() {
            try {
                while (waitRandomTime()) {
                    basket.removeApple();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }        }    }    /////////////////////////////////////////////////////////    public static final Random RANDOM = new Random();    private static void outputThreadMessage(String message, boolean err) {
        if (err) {
            System.err.printf("[%10s] %s\n", Thread.currentThread().getName(), message);
        } else {
            System.out.printf("[%10s] %s\n", Thread.currentThread().getName(), message);
        }
    }    private static boolean waitRandomTime() {
        try {
            Thread.sleep(RANDOM.nextInt(1000) + 500);
            return true;
        } catch (InterruptedException e) {
            e.printStackTrace();
            return false;
        }
    }
}

Answer 1

之前那个有问题，因为控制台的输出并不是严格按照先后顺序来的，所以不能依赖控制台输出来观察多线程的运行，必须先按照先后顺序把消息记下来，然后再一把输出。import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;/**
 * 多线程生产者-消费者示例
 */
public class Basket {    public static final int BASKET_CAPACITY = 5;    private List<String> list = new ArrayList<>();    private Lock lock = new ReentrantLock();    private Condition setter = lock.newCondition(); //篮子为满的条件    private Condition getter = lock.newCondition(); //篮子为空的条件    // 放入苹果
    public void addApple() throws InterruptedException {
        try {
            lock.lock();
            while (list.size() >= BASKET_CAPACITY) {
                addMessage("+++ 篮子已满，等待取出");
                setter.await();
            }
            list.add("红富士");
            addMessage("+++ 放入苹果: 篮子里还有" + list.size());            getter.signalAll();
        } finally {
            lock.unlock();
        }
    }    // 取出苹果
    public void removeApple() throws InterruptedException {
        try {
            lock.lock();
            while (list.size() <= 0) {
                addMessage("--- 篮子已空，等待放入");
                getter.await();
            }
            list.remove(0);
            addMessage("--- 取出苹果: 篮子里还有" + list.size());            setter.signalAll();
        } finally {
            lock.unlock();
        }
    }    /////////////////////////////////////////////////////////    public static void main(String[] args) throws Exception {
        final Basket baskert = new Basket();        // 通过调整 AddAppleTask 和 RemoveAppleTask 的线程数，可以
        // 观察篮子满或空的情况        startTask(new AddAppleTask(baskert));
        startTask(new AddAppleTask(baskert));
        startTask(new AddAppleTask(baskert));        startTask(new RemoveAppleTask(baskert));
        startTask(new RemoveAppleTask(baskert));        System.out.println("线程运行中，请等待 10 秒...");        Thread.sleep(10000);    // 让线程运行 10 秒钟
        stop = true;
        Thread.sleep(2000);     // 等待所有线程停止        outputMessagesWithOrder();       // 按照次序打印消息
    }    private static void startTask(Runnable runnable) {
        Thread thread = new Thread(runnable);
        thread.setDaemon(true);
        thread.start();
    }    /////////////////////////////////////////////////////////    /**
     * 放入苹果线程
     */
    private static class AddAppleTask implements Runnable {        private final Basket basket;        public AddAppleTask(Basket basket) {
            this.basket = basket;
        }        public void run() {
            try {
                while (waitRandomTime()) {
                    basket.addApple();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }    }    /**
     * 取出苹果线程
     */
    private static class RemoveAppleTask implements Runnable {        private final Basket basket;        public RemoveAppleTask(Basket basket) {
            this.basket = basket;
        }        public void run() {
            try {
                while (waitRandomTime()) {
                    basket.removeApple();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }        }    }    /////////////////////////////////////////////////////////    public static final Random RANDOM = new Random();    private static boolean stop = false;    private static List<String> messages = new ArrayList<>();    private static final AtomicInteger serial = new AtomicInteger();    private static synchronized void addMessage(String message) {
        messages.add(String.format("%4d[%8s] %s",
                serial.incrementAndGet(), Thread.currentThread().getName(), message));
    }    private static void outputMessagesWithOrder() {
        Collections.sort(messages);        for (String message : messages) {
            System.out.println(message);
        }
    }    private static boolean waitRandomTime() {
        try {
            Thread.sleep(RANDOM.nextInt(1000) + 500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return !stop;
    }
}

Answer 2

谢谢
不过你的输出结果和预期相同，是不是因为你waitRandomTime方法调用了sleep。为什么不用sleep执行顺序就不对，巧合吗

Answer 3

数量 50 100，500  结果都一样
你代码耗时太低了，应该是计算线程优先级的问题，我这里调到30就能出现你想要的结果，加上Thread.sleep(1000)调到20就能出现你要的结果。