java并发

学习ReentrantLock

一丶什么是ReentrantLock

　　ReentrantLock是java并发包中锁的一种实现, 它是重入锁, 即获取锁之后,自身可再次获取锁, 自身并不会造成死锁, 可以认为它是关键字sychronized的替代品,但它比sychronized有更丰富的功能, 如提供Condition等待, 提供中断等功能. 

二丶ReentrantLock的功能

　　ReentrantLock实现了Lock接口, 因此它有如下功能

　　1. 获取锁

void lock();

　　2. 获取锁, 等待过程可中断

void lockInterruptibly() throws InterruptedException;

　　3. 尝试获取锁, 如果没有获取到锁, 立即返回

boolean tryLock();

　　4. 尝试获取锁, 并且在指定时间内等待, 当超出指定时间后, 或被中断之后立即返回

boolean tryLock(long time, TimeUnit unit) throws InterruptedException;

　　5. 释放锁

void unlock();

　　6. 新建条件

Condition newCondition();

三丶使用例子

　　使用ReentrantLock成为线程安全的阻塞队列

public class BlockingQueue {
    
    private int[] datas;
    private int count;
    private int firstIndex;
    private int endIndex;
    
    private ReentrantLock lock=new ReentrantLock();
    
    // 未空的条件， 等待take
    private final Condition notEmpty = lock.newCondition();
    // 未满的条件， 等待put
    private final Condition notFull = lock.newCondition();
    
    
    public BlockingQueue(int capacity) {
        this.datas = new int[capacity];
        this.count = 0;
    }
    
    public void put(int data) throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly(); // 先获取锁 
        try {
            while(count == datas.length){ //这里需要加上循环判断, 队列已满, 不能存, 释放锁, 挂起等待
                notFull.await();  // 如果条件不满足, 会先释放锁, 挂起当前线程, 直到条件满足被通知唤醒
            }
            enqueue(data);
        }finally {
            lock.unlock();
        }
    }
    
    public int take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly(); // 先获取锁 
        try {
            while(count == 0){  // 这里需要加上循环判断, 个数为0, 不能取, 释放锁, 挂起等待
                notEmpty.await(); // 如果条件不满足, 会先释放锁, 挂起当前线程, 直到条件满足被通知唤醒
            }
            int data=dequeue();
            return data;
        }finally {
            lock.unlock();
        }
    }
    
    private void enqueue(int data){
        datas[endIndex]=data;
        
        
        endIndex++;
        if(endIndex==datas.length){
            endIndex=0;
        }
        
        count++;
        notEmpty.signal();  //condition 发信号，将内部队列的第一个线程移至Lock队列中
    }
    
    private int dequeue(){
        int data=datas[firstIndex];
     
        firstIndex++;
        if(firstIndex==datas.length){
            firstIndex=0;
        }
        
        count--;
        notFull.signal();
        return data;
    }
    
}

　　场景测试类:

public class ReentrantTests {

    public static void main(String[] args) throws InterruptedException {
        // 
        BlockingQueue blockingQueue=new BlockingQueue(20);
        
        Thread producer=new Thread(new ProducerRunnable(blockingQueue, 1));
        Thread consumer1=new Thread(new ConsumerRunnable("消费者1", blockingQueue, 2));
        Thread consumer2=new Thread(new ConsumerRunnable("消费者2", blockingQueue, 3));
        
        
        producer.start();
        consumer1.start();
        consumer2.start();
        
//        producer.join();
        consumer1.join();
        consumer2.join();
    }
    
    
    
}
class ProducerRunnable implements  Runnable{

    private BlockingQueue bq;
    private int interval;
    
    public ProducerRunnable(BlockingQueue bq, int interval) {
        this.bq = bq;
        this.interval=interval;
    }

    @Override public void run() {
        int mix=10000;
        int i=0;
        try {
            while(i<mix){
                this.bq.put(i);
                i++;
                System.out.println("生产者停顿"+interval*100+"ms...");
                Thread.sleep(interval * 100);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


class ConsumerRunnable implements  Runnable{

    private BlockingQueue bq;
    private int interval;
    private String name;

    public ConsumerRunnable(String name,BlockingQueue bq, int interval) {
        this.name = name;
        this.bq = bq;
        this.interval=interval;
    }

    @Override public void run() {
        int mix=10000;
        int i=0;
        try {
            while(i<mix){
                int data=this.bq.take();
                System.out.println(this.name+"获取数据"+data);
                System.out.println(this.name+"停顿"+interval*100+"ms...");
                Thread.sleep(interval * 100);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

　　完整源码: ReentraLock