java volatile 可见行(Visibility)，原子性(Atomicity)，有序性(Ordering)
Tue, Feb 16, 2021
2-minute read
prove java volatile visibility
Volatile
1.1 assume int number = 0; add volatile keyword before changing value of number
code:before add volatile keyword
package com.exa.study.thread;
import java.util.concurrent.TimeUnit;
class MyData {
int number = 0;
public void addTo60() {
this.number = 60;
}
}
/**
*1.prove java volatile visibility
* 1.1 assume int number = 0; add volatile keyword before changing value of number
*/
public class VolatileDemo {
public static void main(String[] args) {
MyData myData = new MyData();
new Thread(() -> {
System.out.println(Thread.currentThread().getName()+"\t come in");
try {
TimeUnit.SECONDS.sleep(3);
} catch (Exception e) {
e.printStackTrace();
}
myData.addTo60();
System.out.println(Thread.currentThread().getName()+"\t update number"+ myData.number);
}, "AAA").start();
// the second main thread
while(myData.number == 0){
// main thread would be waiting until number is not 0
}
System.out.println(Thread.currentThread().getName()+"\t umission is over");
}
}
AAA come in AAA update number60
It shows main thread doesnot know the number has updated to 60.
class MyData {
volatile int number = 0;
public void addTo60() {
this.number = 60;
}
}
Volatile
Java volatile keyword doesn’t means atomic
2.1 atomic :
- An atomic operation is one that cannot be interrupted by the thread
- method was executed successfully or failure
Volatile
atomic means the result would be 20000
However, when run the method twice, we can get two different result, means it is actually making non-atomic operation.
Volatile
