各种锁的理解

公平锁和非公平锁

公平锁：非常公平，线程不能插队
非公平锁，线程可以插队
Lock lock = new ReentrantLock();就是非公平锁

可重入锁

同步方法嵌套，线程在拿到外边锁了，也会获取到里边的锁，

synchronized锁

public class Demo1 {

    public static void main(String[] args) {
        Phone phone = new Phone();
        new Thread(()->{
            phone.send();
        },"a").start();

        new Thread(()->{
            phone.send();
        },"b").start();
    }
}

class Phone{
    public synchronized void send(){
        System.out.println(Thread.currentThread().getName() + "---send");
        call();
    }

    public synchronized void call(){
        System.out.println(Thread.currentThread().getName() + "----call");
    }
}

Lock锁

public class Demo1 {

    public static void main(String[] args) {
        Phone phone = new Phone();
        new Thread(()->{
            phone.send();
        },"a").start();

        new Thread(()->{
            phone.send();
        },"b").start();
    }
}

class Phone{
    Lock lock = new ReentrantLock();

    public  void send(){
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getName() + "---send");
            call();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public  void call(){
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getName() + "----call");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

自旋锁

死锁

public class DiedLockDemo {
    public static void main(String[] args) {
        String strA = "strA";
        String strB = "strB";
        new Thread(new MyDied(strA, strB)).start();
        new Thread(new MyDied(strB, strA)).start();
    }
}


class MyDied implements Runnable{
    private String strA;
    private String strB;

    public MyDied(String strA, String strB) {
        this.strA = strA;
        this.strB = strB;
    }

    @Override
    public void run() {
        synchronized (strA) {
            System.out.println(Thread.currentThread().getName() + "---strA");
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (strB) {
                System.out.println(Thread.currentThread().getName() + "---strB");
            }
        }
    }
}

查看死锁
在死锁情况下，idea的Terminal窗口

idea的Terminal窗口输入jps -l ，查询进程号

然后在输入：jstack 进程号

信息拉到最下边就可以看到死锁的信息