从头认识java-18.6 synchronized在其它对象上同步和ThreadLocal来消除共享对象的同步问题

这一章节我们来介绍在其它对象上同步与ThreadLocal。

前一章节我们使用了

1.synchronized在其它对象上同步

class ThreadA implements Runnable {
private Object object = new Object();

private synchronized void test() throws InterruptedException {
System.out.println("dosomething");
Thread.sleep(5000);
synchronized (object) {
System.out.println("dosomething");
}
}

@Override
public void run() {
while (true) {
try {
test();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

2.ThreadLocal来消除共享对象的同步问题

package com.ray.ch18;

public class Test {

public static void main(String[] args) {
new Thread(new Accessor(new ThreadLocalVarHoder())).start();
new Thread(new Accessor(new ThreadLocalVarHoder())).start();
new Thread(new Accessor(new ThreadLocalVarHoder())).start();
}
}

class Accessor implements Runnable {
private ThreadLocalVarHoder threadLocalVarHoder;

public Accessor(ThreadLocalVarHoder threadLocalVarHoder) {
this.threadLocalVarHoder = threadLocalVarHoder;
}

@Override
public void run() {
for (int i = 0; i < 3; i++) {
threadLocalVarHoder.increment();
System.out.println(Thread.currentThread().getName() + " "
+ threadLocalVarHoder.get());
}
}

}

class ThreadLocalVarHoder {
private static ThreadLocal<Integer> value = new ThreadLocal<Integer>() {
protected Integer initialValue() {
return 0;
}
};

public void increment() {
value.set(value.get() + 1);
}

public int get() {
return value.get();
}
}

输出：

Thread-0 1
Thread-0 2
Thread-0 3
Thread-1 1
Thread-2 1
Thread-2 2
Thread-2 3
Thread-1 2
Thread-1 3

从上面的输出能够看见。每个线程都是读取自己线程上面的副本的值，它的改动这些不涉及原来的对象。

总结：这一章节简介了synchronized在其它对象上同步和ThreadLocal来消除共享对象的同步问题。

这一章节就到这里，谢谢。

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