从头认识多线程-2.2 synchronized持有对象锁与类锁的相同点

这一章节我们来讨论一下synchronized持有对象锁与类锁的相同点。

1.当所有方法都不使用同步的时候

代码清单

package com.ray.deepintothread.ch02.topic_2;public class SynchInstance1 {public static void main(String[] args) throws InterruptedException {MyTestObjectOne myTestObjectOne = new MyTestObjectOne();for (int i = 0; i < 5; i++) {ThreadOne threadTwo = new ThreadOne(myTestObjectOne);Thread thread = new Thread(threadTwo);thread.setName("" + i);thread.start();}}}class ThreadOne implements Runnable {private MyTestObjectOne myTestObjectOne;public ThreadOne(MyTestObjectOne myTestObjectOne) {this.myTestObjectOne = myTestObjectOne;}@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {myTestObjectOne.test1();} else {myTestObjectOne.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectOne {public void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");Thread.sleep(200);System.out.println(Thread.currentThread().getName() + " method test1 end");}public void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");Thread.sleep(200);System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

0 method test1 begin
0 method test1 waiting
4 method test1 begin
4 method test1 waiting
2 method test1 begin
2 method test1 waiting
1 method test2 begin
1 method test2 waiting
3 method test2 begin
3 method test2 waiting
0 method test1 end
4 method test1 end
2 method test1 end
1 method test2 end
3 method test2 end

持有类锁的情况：

package com.ray.deepintothread.ch02.topic_3;public class SynchInstance1 {public static void main(String[] args) throws InterruptedException {for (int i = 0; i < 5; i++) {ThreadOne threadTwo = new ThreadOne();Thread thread = new Thread(threadTwo);thread.setName("" + i);thread.start();}}}class ThreadOne implements Runnable {@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {MyTestObjectOne.test1();} else {MyTestObjectOne.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectOne {public static void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");Thread.sleep(200);System.out.println(Thread.currentThread().getName() + " method test1 end");}public static void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");Thread.sleep(200);System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

0 method test1 begin
0 method test1 waiting
2 method test1 begin
2 method test1 waiting
3 method test2 begin
3 method test2 waiting
1 method test2 begin
1 method test2 waiting
4 method test1 begin
4 method test1 waiting
2 method test1 end
3 method test2 end
0 method test1 end
1 method test2 end
4 method test1 end

从两个输出可以看见，方法是交叉的执行，没有任何同步在里面的

2.当所有方法都使用同步的时候

代码清单

package com.ray.deepintothread.ch02.topic_2;public class SynchInstance2 {public static void main(String[] args) throws InterruptedException {MyTestObjectTwo myTestObjectTwo = new MyTestObjectTwo();for (int i = 0; i < 5; i++) {ThreadTwo threadTwo = new ThreadTwo(myTestObjectTwo);Thread thread = new Thread(threadTwo);thread.setName("" + i);thread.start();}}}class ThreadTwo implements Runnable {private MyTestObjectTwo myTestObjectTwo;public ThreadTwo(MyTestObjectTwo myTestObjectTwo) {this.myTestObjectTwo = myTestObjectTwo;}@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {myTestObjectTwo.test1();} else {myTestObjectTwo.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectTwo {public synchronized void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");System.out.println(Thread.currentThread().getName() + " method test1 end");}public synchronized void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

1 method test2 begin
1 method test2 waiting
1 method test2 end
0 method test1 begin
0 method test1 waiting
0 method test1 end
2 method test1 begin
2 method test1 waiting
2 method test1 end
4 method test1 begin
4 method test1 waiting
4 method test1 end
3 method test2 begin
3 method test2 waiting
3 method test2 end

package com.ray.deepintothread.ch02.topic_3;public class SynchInstance2 {public static void main(String[] args) throws InterruptedException {for (int i = 0; i < 5; i++) {ThreadTwo threadTwo = new ThreadTwo();Thread thread = new Thread(threadTwo);thread.setName("" + i);thread.start();}}}class ThreadTwo implements Runnable {@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {MyTestObjectTwo.test1();} else {MyTestObjectTwo.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectTwo {public static synchronized void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");System.out.println(Thread.currentThread().getName() + " method test1 end");}public static synchronized void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

0 method test1 begin
0 method test1 waiting
0 method test1 end
1 method test2 begin
1 method test2 waiting
1 method test2 end
3 method test2 begin
3 method test2 waiting
3 method test2 end
2 method test1 begin
2 method test1 waiting
2 method test1 end
4 method test1 begin
4 method test1 waiting
4 method test1 end

从输出和debug发现，每一个方法都是按照顺序执行，同步起效

但是比较奇怪的是，每次都是整个方法执行完了才到下一个方法执行

按照平常的执行，应该是像上面一样，交叉的执行，因为我们使用多线程而且是访问不同的方法，如果同步是方法级别，应该可以想象到线程1访问test1的时候，我线程2同时可以访问test2，如果不是，那么synchronized持有的是锁不是方法级别的，而是对象级别或者类级别，而一般类级别对于的是静态方法和代码块。

3.特点

（1）所有同步方法只能按顺序执行，上面的例子有所演示

（2）synchronized只同步标记的方法，不标记的还是不同步

package com.ray.deepintothread.ch02.topic_2;public class SynchInstance3 {public static void main(String[] args) throws InterruptedException {MyTestObjectThree myTestObjectThree = new MyTestObjectThree();for (int i = 0; i < 5; i++) {ThreadThree threadThree = new ThreadThree(myTestObjectThree);Thread thread = new Thread(threadThree);thread.setName("" + i);thread.start();}}}class ThreadThree implements Runnable {private MyTestObjectThree myTestObjectThree;public ThreadThree(MyTestObjectThree myTestObjectThree) {this.myTestObjectThree = myTestObjectThree;}@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {myTestObjectThree.test1();} else {myTestObjectThree.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectThree {public synchronized void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");System.out.println(Thread.currentThread().getName() + " method test1 end");}public void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

0 method test1 begin
3 method test2 begin
3 method test2 waiting
3 method test2 end
1 method test2 begin
1 method test2 waiting
1 method test2 end
0 method test1 waiting
0 method test1 end
2 method test1 begin
2 method test1 waiting
2 method test1 end
4 method test1 begin
4 method test1 waiting
4 method test1 end

package com.ray.deepintothread.ch02.topic_3;public class SynchInstance3 {public static void main(String[] args) throws InterruptedException {MyTestObjectThree myTestObjectThree = new MyTestObjectThree();for (int i = 0; i < 5; i++) {ThreadThree threadThree = new ThreadThree(myTestObjectThree);Thread thread = new Thread(threadThree);thread.setName("" + i);thread.start();}}}class ThreadThree implements Runnable {private MyTestObjectThree myTestObjectThree;public ThreadThree(MyTestObjectThree myTestObjectThree) {this.myTestObjectThree = myTestObjectThree;}@Overridepublic void run() {try {if (Integer.parseInt(Thread.currentThread().getName()) % 2 == 0) {myTestObjectThree.test1();} else {myTestObjectThree.test2();}} catch (InterruptedException e) {e.printStackTrace();}}}class MyTestObjectThree {public synchronized void test1() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test1 begin");System.out.println(Thread.currentThread().getName() + " method test1 waiting");System.out.println(Thread.currentThread().getName() + " method test1 end");}public void test2() throws InterruptedException {System.out.println(Thread.currentThread().getName() + " method test2 begin");System.out.println(Thread.currentThread().getName() + " method test2 waiting");System.out.println(Thread.currentThread().getName() + " method test2 end");}}

输出：

0 method test1 begin
0 method test1 waiting
0 method test1 end
2 method test1 begin
2 method test1 waiting
2 method test1 end
1 method test2 begin
1 method test2 waiting
4 method test1 begin
4 method test1 waiting
4 method test1 end
1 method test2 end
3 method test2 begin
3 method test2 waiting
3 method test2 end

总结：这一章节我们讨论了synchronized持有锁的情况。

这一章节就到这里，谢谢

------------------------------------------------------------------------------------

我的github：https://github.com/raylee2015/DeepIntoThread

目录：http://blog.csdn.net/raylee2007/article/details/51204573