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