多线程同步之 锁对象 的理解

package function.thread;

 

class ThreadDemo1 implements Runnable {

 

public void run() {

// 为了更清楚地看到不正确的结果，这里放一个大的循环

String ThreadName = Thread.currentThread().getName();

if (ThreadName.equals("Thread-0")) {

System.out.println(ThreadName+" enter synchronized before.....\n");

synchronized (this) {//锁住的不是当前整个对象，而是和当前对象里同步相关的内容

System.out.println(ThreadName+" enter.....");

try {

for(int i = 0;i<10;i++){

System.out.println(ThreadName+" print ....");

// 为了演示产生的问题，这里设置一次睡眠

Thread.sleep(200);

}

 

} catch (InterruptedException e) {

}

// 输出结果

System.out.println(ThreadName+" go off.....\n");

}

} else if (ThreadName.equals("Thread-1")) {

//即使竞争线程进入了上述if 分支，并且进入到了syschronize块里

//另外的线程也可以可以执行如下syschronize之前的内容

//所以锁对象是一个概念，是一种机制，而不是字面上理解的锁住整个对象

try {

for(int j =0;j<10;j++){

System.out.println(ThreadName+" enter synchronized before....."+j);

Thread.sleep(200);

}

} catch (InterruptedException e) {

e.printStackTrace();

}

synchronized (this) {

System.out.println(ThreadName+" enter.....");

try {

for(int i = 0;i<10;i++){

System.out.println(ThreadName+" print......");

Thread.sleep(200);

}

 

} catch (InterruptedException e) {

}

System.out.println(ThreadName+" go off.....\n");

}

}

}

}

 

public class ThreadSync1 {

public static void main(String args[]) {

ThreadDemo1 th1 = new ThreadDemo1();

new Thread(th1).start();

new Thread(th1).start();

 

}

}

 

运行结果：

Thread-0 enter synchronized before.....

 

Thread-1 enter synchronized before.....0

Thread-0 enter.....

Thread-0 print ....

Thread-0 print ....

Thread-1 enter synchronized before.....1

Thread-0 print ....

Thread-1 enter synchronized before.....2

Thread-0 print ....

Thread-1 enter synchronized before.....3

Thread-0 print ....

Thread-1 enter synchronized before.....4

Thread-0 print ....

Thread-1 enter synchronized before.....5

Thread-0 print ....

Thread-1 enter synchronized before.....6

Thread-0 print ....

Thread-1 enter synchronized before.....7

Thread-0 print ....

Thread-1 enter synchronized before.....8

Thread-0 print ....

Thread-1 enter synchronized before.....9

Thread-0 go off.....

 

Thread-1 enter.....

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 print......

Thread-1 go off.....