引言

　　生產者和消費者問題是線程模型中的經典問題：生產者和消費者在同一時間段內共用同一個存儲空間，如下圖所示，生產者向空間里存放數據，而消費者取用數據，如果不加以協調可能會出現以下情況：

生產者消費者圖

　　存儲空間已滿，而生產者占用着它，消費者等着生產者讓出空間從而去除產品，生產者等着消費者消費產品，從而向空間中添加產品。互相等待，從而發生死鎖。

JAVA解決線程模型的三種方式

　　1、wait()和notify()

import java.util.LinkedList;

public class ProducerConsumer {
    private LinkedList<Object> storeHouse = new LinkedList<Object>();
    private int MAX = 10;

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Comsumer().start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                synchronized (storeHouse) {
                    try {
                        while (storeHouse.size() == MAX) {
                            System.out.println("storeHouse is full , please wait");
                            storeHouse.wait();
                        }
                        Object newOb = new Object();
                        if (storeHouse.add(newOb)) {
                            System.out.println("Producer put a Object to storeHouse");
                            Thread.sleep((long) (Math.random() * 3000));
                            storeHouse.notify();
                        }
                    } catch (InterruptedException ie) {
                        System.out.println("producer is interrupted!");
                    }

                }
            }
        }
    }

    class Comsumer extends Thread {
        public void run() {
            while (true) {
                synchronized (storeHouse) {
                    try {
                        while (storeHouse.size() == 0) {
                            System.out.println("storeHouse is empty , please wait");
                            storeHouse.wait();
                        }
                        storeHouse.removeLast();
                        System.out.println("Comsumer get  a Object from storeHouse");
                        Thread.sleep((long) (Math.random() * 3000));
                        storeHouse.notify();
                    } catch (InterruptedException ie) {
                        System.out.println("Consumer is interrupted");
                    }

                }
            }

        }
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer pc = new ProducerConsumer();
        pc.start();
    }
}

 

　　2、await()和signal()，即線程鎖的方式

package sort;

import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ProducerConsumer {
    private LinkedList<Object> myList = new LinkedList<Object>();
    private int MAX = 10;
    private final Lock lock = new ReentrantLock();
    private final Condition full = lock.newCondition();
    private final Condition empty = lock.newCondition();

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Consumer().start();
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer s2 = new ProducerConsumer();
        s2.start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                lock.lock();
                try {
                    while (myList.size() == MAX) {
                        System.out.println("warning: it's full!");
                        full.await();
                    }
                    Object o = new Object();
                    if (myList.add(o)) {
                        System.out.println("Producer: " + o);
                        empty.signal();
                    }
                } catch (InterruptedException ie) {
                    System.out.println("producer is interrupted!");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

    class Consumer extends Thread {
        public void run() {
            while (true) {
                lock.lock();
                try {
                    while (myList.size() == 0) {
                        System.out.println("warning: it's empty!");
                        empty.await();
                    }
                    Object o = myList.removeLast();
                    System.out.println("Consumer: " + o);
                    full.signal();
                } catch (InterruptedException ie) {
                    System.out.println("consumer is interrupted!");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

}

 

　　3、阻塞隊列的方式

import java.util.concurrent.*;

public class ProducerConsumer {
    // 建立一個阻塞隊列
    private LinkedBlockingQueue<Object> queue = new LinkedBlockingQueue<Object>(10);

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Consumer().start();
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer s3 = new ProducerConsumer();
        s3.start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                try {
                    Object o = new Object();
                    // 取出一個對象
                    queue.put(o);
                    System.out.println("Producer: " + o);
                } catch (InterruptedException e) {
                    System.out.println("producer is interrupted!");
                }
                // }
            }
        }
    }

    class Consumer extends Thread {
        public void run() {
            while (true) {
                try {
                    // 取出一個對象
                    Object o = queue.take();
                    System.out.println("Consumer: " + o);
                } catch (InterruptedException e) {
                    System.out.println("producer is interrupted!");
                }
                // }
            }
        }
    }

}

結論

  三種方式原理一致，都是對獨占空間加鎖，阻塞和喚醒線程，第一種方式比較傳統，第三種方式最簡單，只需存儲和取用，線程同步的操作交由LinkedBlockingQueue全權處理。