引言
生产者和消费者问题是线程模型中的经典问题：生产者和消费者在同一时间段内共用同一个存储空间，如下图所示，生产者向空间里存放数据，而消费者取用数据，如果不加以协调可能会出现以下情况：
生产者消费者图
存储空间已满，而生产者占用着它，消费者等着生产者让出空间从而去除产品，生产者等着消费者消费产品，从而向空间中添加产品。互相等待，从而发生死锁。
JAVA解决线程模型的三种方式
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()，即线程锁的方式
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、阻塞队列的方式
import java.util.concurrent.*;public class ProducerConsumer { // 建立一个阻塞队列
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(); // 取出一个对象 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 { // 取出一个对象
Object o = queue.take();
System.out.println("Consumer: " + o);
} catch (InterruptedException e) {
System.out.println("producer is interrupted!");
} // } }
}
}
}
结论
三种方式原理一致，都是对独占空间加锁，阻塞和唤醒线程，第一种方式比较传统，第三种方式最简单，只需存储和取用，线程同步的操作交由LinkedBlockingQueue全权处理。
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