目录

synchronized

面向对象改进

synchronized加在方法上

线程八锁

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synchronized

线程1上锁之后，线程2无法获取锁不能够执行临时区，线程2阻塞等待线程1完成释放锁之后才能够使用。可以把synchronize类比成一个房间，每次有锁的人才能够进入房间做事情，就算cpu时间片用完，只要没有这个锁那么其他线程是无法进入房间的。当用完之后就会释放锁，并且唤醒那些阻塞的线程

解决

  @Slf4jpublic class Test {​static int counter = 0 ;​// 定义锁对象static Object lock = new Object();​public static void main(String[] args) throws InterruptedException {Thread t1 = new Thread(() ->{for (int i = 0; i < 5000; i++) {synchronized (lock){       // 上锁counter ++ ;}}});​Thread t2= new Thread(() ->{for (int i = 0; i < 5000; i++) {synchronized (lock){counter -- ;}}});​​t1.start();t2.start();t1.join();t2.join();System.out.println(counter);​}​}

synchonized实际上是使用对象锁保证了临界区内代码的原子性,临界区是不可分割的，不会被线程切换打断

面向对象改进

  @Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Room room = new Room();​Thread t1 = new Thread(() ->{for (int i = 0; i < 5000; i++) {room.increment();}});​Thread t2= new Thread(() ->{for (int i = 0; i < 5000; i++) {room.decrement();}});​​t1.start();t2.start();t1.join();t2.join();System.out.println(room.getCounter());​}​}​​class Room{int count = 0 ;​public void increment(){synchronized (this){count ++ ;}}​public void decrement(){synchronized (this){count --;}}​public int getCounter(){synchronized (this){return count;}}}

synchronized加在方法上

  class c1{public synchronized void test(){} }​class c1{public void test(){synchronized (this){​}}}​二者等价,锁住的是this对象

加载静态方法上相当于锁住类对象

线程八锁

情况1 ： 1 2或者2 1

  ​@Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();new Thread(() -> {log.debug("begin");n1.b();}).start();}​}​​@Slf4jclass Number{public synchronized void a(){log.debug("1");}​public synchronized void b(){log.debug("2");}​}

情况2 : 1s后1 2 或 1s后2 1

  ​@Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();new Thread(() -> {log.debug("begin");n1.b();}).start();​}​}​@Slf4jclass Number{public synchronized void a() throws InterruptedException {Thread.sleep(1000);log.debug("1");}​public synchronized void b(){log.debug("2");}​​}

情况3 : 3 ,1s后 1 2 || 3 , 2 1s后打印1 || 2 , 3 1s后打印1

  @Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();new Thread(() -> {log.debug("begin");n1.b();}).start();​new Thread(() -> {log.debug("begin");n1.c();}).start();​}​}​@Slf4jclass Number{public synchronized void a()  {try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public synchronized void b(){log.debug("2");}​public  void c(){log.debug("3");}​​}

情况4 : 先2，1s后打印1

  @Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();Number n2 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();​new Thread(() -> {log.debug("begin");n2.b();}).start();​​​}​}@Slf4jclass Number{public synchronized void a()  {try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public synchronized void b(){log.debug("2");}​​}

情况5 : 先2，1s后打印1

  @Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();​new Thread(() -> {log.debug("begin");n1.b();}).start();}​}​@Slf4jclass Number{public static synchronized void a()  {     // 锁住的是类对象try { Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public synchronized void b(){log.debug("2");}​​}​​

情况6 : 1s后打印1 后2 || 2 1s后打印1

  @Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();​new Thread(() -> {log.debug("begin");n1.b();}).start();​}​}​@Slf4jclass Number{public static synchronized void a()  {try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public static synchronized void b(){log.debug("2");}​}

情况7 : 先2 1s后打印1

  import lombok.extern.slf4j.Slf4j;​​@Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();Number n2 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();​new Thread(() -> {log.debug("begin");n2.b();}).start();​​​}​}​​@Slf4jclass Number{public static synchronized void a()  {try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public  synchronized void b(){log.debug("2");}​​}​​

情况8 : 1s后打印1 后2 || 2 1s后打印1

  import lombok.extern.slf4j.Slf4j;​​@Slf4jpublic class Test {public static void main(String[] args) throws InterruptedException {Number n1 = new Number();Number n2 = new Number();new Thread(() -> {log.debug("begin");n1.a();}).start();​new Thread(() -> {log.debug("begin");n2.b();}).start();​}​}​@Slf4jclass Number{public static synchronized void a()  {try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}log.debug("1");}​public static synchronized void b(){log.debug("2");}​}