标签:Java INT start 理解 volatile Got MY Incrementing Change
volatile修饰符修饰变量,不可以修饰类和方法,volatile不是线程安全的,但是一写多读的多线程情况下是线程安全的。
多线程的特性:
- 可见性 各线程之间的变量会同步到主线程
- 原子性
volatile是可见的,但不是原子的。
synchronized是可见的也是原子的。
一个线程写,多个线程读可以使用volatile,这样的情况下的多线程是安全的。
多个线程写,多个线程读不能使用volatile,这样的情况下的多线程是不安全的。
package crelle.test.juc; /** * 一个线程写,多个线程读 线程安全 */ public class VolatileSingleWriterTest { private static volatile int MY_INT = 0; public static void main(String[] args) { new ChangeListener().start(); new ChangeListener().start(); new ChangeListener().start(); new ChangeListener().start(); new ChangeListener().start(); new ChangeListener().start(); new ChangeMaker().start(); } static class ChangeListener extends Thread { @Override public void run() { int local_value = MY_INT; while ( local_value < 5){ if( local_value!= MY_INT){ System.out.println("Got Change for MY_INT : "+ MY_INT); local_value= MY_INT; } } } } static class ChangeMaker extends Thread{ @Override public void run() { int local_value = MY_INT; while (MY_INT <5){ System.out.println("Incrementing MY_INT to : "+( local_value+1)); MY_INT = ++local_value; try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } } } }
结果: Incrementing MY_INT to : 1 Got Change for MY_INT : 1 Got Change for MY_INT : 1 Got Change for MY_INT : 1 Got Change for MY_INT : 1 Got Change for MY_INT : 1 Got Change for MY_INT : 1 Incrementing MY_INT to : 2 Got Change for MY_INT : 2 Got Change for MY_INT : 2 Got Change for MY_INT : 2 Got Change for MY_INT : 2 Got Change for MY_INT : 2 Got Change for MY_INT : 2 Incrementing MY_INT to : 3 Got Change for MY_INT : 3 Got Change for MY_INT : 3 Got Change for MY_INT : 3 Got Change for MY_INT : 3 Got Change for MY_INT : 3 Got Change for MY_INT : 3 Incrementing MY_INT to : 4 Got Change for MY_INT : 4 Got Change for MY_INT : 4 Got Change for MY_INT : 4 Got Change for MY_INT : 4 Got Change for MY_INT : 4 Got Change for MY_INT : 4 Incrementing MY_INT to : 5 Got Change for MY_INT : 5 Got Change for MY_INT : 5 Got Change for MY_INT : 5 Got Change for MY_INT : 5 Got Change for MY_INT : 5 Got Change for MY_INT : 5 Process finished with exit code 0
package crelle.test.juc; /** * 多个线程写,多个线程读 线程不安全 */ public class VolatileMultiWriterTest { private static volatile int MY_INT = 0; public static void main(String[] args) { new ChangeListener().start(); new ChangeMaker().start(); new ChangeMaker().start(); new ChangeMaker().start(); new ChangeMaker().start(); new ChangeMaker().start(); new ChangeMaker().start(); } static class ChangeListener extends Thread { @Override public void run() { int local_value = MY_INT; while ( local_value < 5){ if( local_value!= MY_INT){ System.out.println("Got Change for MY_INT : "+ MY_INT); local_value= MY_INT; } } } } static class ChangeMaker extends Thread{ @Override public void run() { int local_value = MY_INT; while (MY_INT <5){ System.out.println("Incrementing MY_INT to : "+( local_value+1)); MY_INT = ++local_value; try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } } } }
结果:
Incrementing MY_INT to : 1 Incrementing MY_INT to : 1 Incrementing MY_INT to : 1 Got Change for MY_INT : 1 Incrementing MY_INT to : 2 Incrementing MY_INT to : 2 Incrementing MY_INT to : 2 Got Change for MY_INT : 2 Incrementing MY_INT to : 2 Incrementing MY_INT to : 2 Incrementing MY_INT to : 3 Incrementing MY_INT to : 2 Incrementing MY_INT to : 3 Incrementing MY_INT to : 3 Got Change for MY_INT : 3 Incrementing MY_INT to : 3 Incrementing MY_INT to : 3 Incrementing MY_INT to : 4 Incrementing MY_INT to : 3 Incrementing MY_INT to : 4 Incrementing MY_INT to : 4 Got Change for MY_INT : 4 Incrementing MY_INT to : 4 Incrementing MY_INT to : 4 Incrementing MY_INT to : 5 Got Change for MY_INT : 5 Incrementing MY_INT to : 4 Incrementing MY_INT to : 5 Incrementing MY_INT to : 5 Process finished with exit code 0
标签:Java,INT,start,理解,volatile,Got,MY,Incrementing,Change 来源: https://www.cnblogs.com/crelle/p/13304832.html
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