并发编程总结

1、ABCD四个线程按照是顺序执行的方法要用join().

2、lock锁的用法：

Lock lock = ...;
lock.lock();
try{
    //处理任务
}catch(Exception ex){

}finally{
    lock.unlock();   //释放锁
}

这是一个个模板，lock的实现类是ReentrantLock，现在我们来一个简单的demo

public class LockThread {
    Lock lock = new ReentrantLock(); 
    public void lock(String name) {  
        // 获取锁  
        lock.lock();  
        try {  
            System.out.println(name + " get the lock");  
            // 访问此锁保护的资源  
        } finally {  
            // 释放锁  
            lock.unlock();  
            System.out.println(name + " release the lock");  
        }  
    }  

    public static void main(String[] args) {
        LockThread lt = new LockThread();  
        new Thread(() -> lt.lock("A")).start();  
        new Thread(() -> lt.lock("B")).start();  
    }
}

当然，他的优点可以使读写分离锁，代码安排上

class Queue {
    //共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。
    private Object data = null;

    ReadWriteLock lock = new ReentrantReadWriteLock();

    // 读数据
    public void get() {
        // 加读锁
        lock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + " be ready to read data!");
            Thread.sleep((long) (Math.random() * 1000));
            System.out.println(Thread.currentThread().getName() + " have read data :" + data);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 释放读锁
            lock.readLock().unlock();
        }
    }

    // 写数据
    public void put(Object data) {
        // 加写锁
        lock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + " be ready to write data!");
            Thread.sleep((long) (Math.random() * 1000));
            this.data = data;
            System.out.println(Thread.currentThread().getName() + " have write data: " + data);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 释放写锁
            lock.writeLock().unlock();
        }

    }
}

public class ReadWriteLockDemo {
    public static void main(String[] args) {
        final Queue queue = new Queue();
        //一共启动6个线程，3个读线程，3个写线程
        for (int i = 0; i < 3; i++) {
            //启动1个读线程
            new Thread() {
                public void run() {
                    while (true) {
                        queue.get();
                    }
                }

            }.start();
            //启动1个写线程
            new Thread() {
                public void run() {
                    while (true) {
                        queue.put(new Random().nextInt(10000));
                    }
                }
            }.start();
        }
    }
}

对于其他线程知识还有sleep和wait的区别，sleep就是睡觉还占着床，wait就是你先占那里等一会儿，他会释放锁。