第6章 多线程锁

6.1 synchronized

 

 

6.2 公平锁和非公平锁

源码：

 

 

6.3 可重入锁

6.3.1 synchronized(隐式)

package JUC.lock;

public class SyncLockDemo {

    public synchronized void add() {
        add();
    }

    public static void main(String[] args) {

        //递归调用，栈溢出
//        new SyncLockDemo().add();

        // synchronized
        Object o = new Object();
        new Thread(() -> {
            synchronized (o) {
                System.out.println(Thread.currentThread().getName()+" 外层");

                synchronized (o) {
                    System.out.println(Thread.currentThread().getName()+" 中层");

                    synchronized (o) {
                        System.out.println(Thread.currentThread().getName()+" 内层");
                    }
                }
            }

        }, "t1").start();
    }
}

6.3.2 Lock(显式)

package JUC.lock;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockDemo {

    public static void main(String[] args) {
        //Lock演示可重入锁
        Lock lock = new ReentrantLock();
        //创建线程
        new Thread(() -> {
            try {
                //上锁
                lock.lock();
                System.out.println(Thread.currentThread().getName()+" 外层");

                try {
                    //上锁
                    lock.lock();
                    System.out.println(Thread.currentThread().getName()+" 内层");
                } finally {
                    //释放锁
                    //如果释放锁这里注释掉，那么底下的aa线程不会执行
                    lock.unlock();
                }
            } finally {
                //释放锁
                lock.unlock();
            }
        },"t1").start();

        new Thread(() -> {
            lock.lock();
            System.out.println("aaaa");
            lock.unlock();
        },"aa").start();

    }

}

 

 

6.4 死锁

 

 

 

package JUC.lock;

import java.util.concurrent.TimeUnit;

public class DeadLock {

    //创建两个对象
    static Object a = new Object();
    static Object b = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            synchronized (a) {
                System.out.println(Thread.currentThread().getName()+ " 持有锁a，试图获取锁b");
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (b) {
                    System.out.println(Thread.currentThread().getName()+ " 获取锁b");
                }
            }
        },"A").start();

        new Thread(() -> {
            synchronized (b) {
                System.out.println(Thread.currentThread().getName()+ " 持有锁b，试图获取锁a");
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (a) {
                    System.out.println(Thread.currentThread().getName()+ " 获取锁s");
                }
            }
        },"B").start();
    }
}