【Java多线程系列三】实现线程同步的方法

两种实现线程同步的方法

方法	特性
synchronized	不需要显式的加锁，易实现
ReentrantLock	需要显式地加解锁，灵活性更好，性能更优秀，结合Condition可实现多种条件锁

package com.concurrent.test;

import java.util.Stack;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Description: 三种方法实现生产者/消费者
 */
public class ThreadSynchronizeTest {

    public static void main(String[] args) {
        ProducerConsumer producerConsumer = new ProducerConsumerViaBlockingQueue();
        producerConsumer.test();
    }
}

abstract class ProducerConsumer {
    protected int capacity = 10;
    protected int element = 0;

    protected abstract void produce() throws InterruptedException;

    protected abstract void consume() throws InterruptedException;

    public void test() {
        Thread producer = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        produce();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });

        Thread consumer = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        consume();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

            }
        });

        producer.start();
        consumer.start();

    }
}

/**
 * 方法一：ReentrantLock结合Condition
 */
class ProducerConsumerViaReentrantLock extends ProducerConsumer {
    private Stack<Integer> stack = new Stack<>();
    private ReentrantLock lock = new ReentrantLock();
    private Condition notFull = lock.newCondition();
    private Condition notEmpty = lock.newCondition();

    @Override
    protected void produce() throws InterruptedException {
        try {
            lock.lock();
            if (stack.size() == capacity) {
                notFull.await();
            }

            ++element;
            System.out.println(Thread.currentThread().getId() + "," + Thread.currentThread().getName() + " produce " + element);
            stack.push(element);
            notEmpty.signalAll();
            Thread.sleep(1000L);
        } finally {
            lock.unlock();
        }
    }

    @Override
    protected void consume() throws InterruptedException {
        try {
            lock.lock();
            if (stack.isEmpty()) {
                notEmpty.await();
            }
            int element = stack.pop();
            System.out.println(Thread.currentThread().getId() + "," + Thread.currentThread().getName() + " consume " + element);
            notFull.signalAll();
        } finally {
            lock.unlock();
        }
    }

}

/**
 * 方法二：synchronized 结合  wait、notify、notifyAll
 */
class ProducerConsumerViaObjectLock extends ProducerConsumer {

    private Stack<Integer> stack = new Stack<>();
    private Object lock = new Object();

    @Override
    protected void produce() throws InterruptedException {
        /*
         * 1,lock为监视器
         * 2,wait/notify/notifyAll方法必须在synchronized块内调用
         * 3,调用wait/notify/notifyAll方法但不持有监视器的使用权将会抛出java.lang.IllegalMonitorStateException
         */
        synchronized (lock) {
            if (stack.size() == capacity) {
                lock.wait();
            }

            ++element;
            System.out.println(Thread.currentThread().getId() + "," + Thread.currentThread().getName() + " produce " + element);
            stack.push(element);
            lock.notifyAll();
            Thread.sleep(1000L);
        }
    }

    @Override
    protected void consume() throws InterruptedException {
        synchronized (lock) {
            if (stack.isEmpty()) {
                lock.wait();
            }

            int element = stack.pop();
            System.out.println(Thread.currentThread().getId() + "," + Thread.currentThread().getName() + " consume " + element);
            lock.notifyAll();
        }
    }
}

/**
 * 方法三：BlockingQueue
 */
class ProducerConsumerViaBlockingQueue extends ProducerConsumer {

    private BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(capacity);

    @Override
    protected void produce() throws InterruptedException {
        ++element;
        System.out.println(Thread.currentThread().getId() + "," + Thread.currentThread().getName() + " produce " + element);
        queue.put(element);
        Thread.sleep(1000L);
    }

    @Override
    protected void consume() throws InterruptedException {
        int element = queue.take();
        System.out.println(Thread.currentThread().getId() + " consume " + element);
        Thread.sleep(10000L);
    }
}