1 原始构成

synchronized是关键字属于JVM层面， monitorenter(底层是通过monitor对象来完成，其wait/notify 等方法也依赖于monitor对象只有在同步块或方法中才能调wait/notify等方法） monitorexit

Lock是具体类(java.util.concurrent.locks.Lock)是api层面的锁

2 使用方法

synchronized不需要用户去手动释放锁，当synchronized 代码执行完后系统会自动让线程释放对锁的占用

ReentrantLock则需要用户去手动释放锁若没有主动释放锁，就有可能导致出现死锁现象。

需要Lock()和unLock()方法配合try/finally语句块来完成。

3 等待是否可中断

synchronized不可中断，除非抛出异常或者正常运行完成

ReentrantLock可中断

1. 设置超时方法tryLock(long timeout, TimeUnit unit)
2. lockInterruptibly()放代码块中，调用interrupt() 方法可中断

4 加锁是否公平

synchronized非公平锁

ReentrantLock两者都可以，默认非公平锁，构造方法可以传入boolean值，true 为公平锁，false为非公平锁

5 锁绑定多个条f件condition

synchronized没有

ReentrantLock用来实现分组唤醒需要唤醒的线程们，可以精确唤醒，而不是像synchronized要么随机唤醒一个线程 要么唤醒全部线程。 案例： A->B->C三个线程 依次打印 A打5次 B打10次 C打15次 循环打印10次

public class Demo16 {

    public static void main(String[] args) throws InterruptedException {
        Share share = new Share();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.aPrint5();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "AA").start();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.bPrint10();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "BB").start();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.cPrint15();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "CC").start();

    }
}

class Share {

    private Integer number = 1;

    private Lock lock = new ReentrantLock();
    private Condition c1 = lock.newCondition();
    private Condition c2 = lock.newCondition();
    private Condition c3 = lock.newCondition();

    public void aPrint5() throws InterruptedException {
        lock.lock();
        try {
            while (number != 1) {
                c1.await();
            }

            for (int i = 0; i < 5; i++) {
                System.out.println(Thread.currentThread().getName());
            }

            number = 2;
            c2.signal();
        }finally {
            lock.unlock();
        }
    }

    public void bPrint10() throws InterruptedException {
        lock.lock();
        try {
            while (number != 2) {
                c2.await();
            }

            for (int i = 0; i < 10; i++) {
                System.out.println(Thread.currentThread().getName());
            }

            number = 3;
            c3.signal();
        }finally {
            lock.unlock();
        }

    }

    public void cPrint15() throws InterruptedException {
        lock.lock();
        try {
            while (number != 3) {
                c3.await();
            }

            for (int i = 0; i < 15; i++) {
                System.out.println(Thread.currentThread().getName());
            }

            number = 1;
            c1.signal();
        }finally {
            lock.unlock();
        }

    }
}