Volatile只保证所有线程，甚至线程本身，都是递增的。例如:计数器在同一时间看到变量的同一面。它不是用来代替同步或原子或其他东西，它完全使读取同步。请不要将其与其他java关键字进行比较。如下例所示，volatile变量操作也是原子性的，它们会立即失败或成功。

package io.netty.example.telnet;

import java.util.ArrayList;
import java.util.List;

public class Main {

    public static volatile  int a = 0;
    public static void main(String args[]) throws InterruptedException{

        List<Thread> list = new  ArrayList<Thread>();
        for(int i = 0 ; i<11 ;i++){
            list.add(new Pojo());
        }

        for (Thread thread : list) {
            thread.start();
        }

        Thread.sleep(20000);
        System.out.println(a);
    }
}
class Pojo extends Thread{
    int a = 10001;
    public void run() {
        while(a-->0){
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Main.a++;
            System.out.println("a = "+Main.a);
        }
    }
}

即使你放不放，结果也总会不一样。但是，如果您像下面那样使用AtomicInteger，结果将始终相同。同步也是如此。

    package io.netty.example.telnet;

    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.atomic.AtomicInteger;

    public class Main {

        public static volatile  AtomicInteger a = new AtomicInteger(0);
        public static void main(String args[]) throws InterruptedException{

            List<Thread> list = new  ArrayList<Thread>();
            for(int i = 0 ; i<11 ;i++){
                list.add(new Pojo());
            }

            for (Thread thread : list) {
                thread.start();
            }

            Thread.sleep(20000);
            System.out.println(a.get());

        }
    }
    class Pojo extends Thread{
        int a = 10001;
        public void run() {
            while(a-->0){
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Main.a.incrementAndGet();
                System.out.println("a = "+Main.a);
            }
        }
    }

Volatile具有内存可见性的语义。基本上，volatile字段的值在写操作完成后对所有读取器(特别是其他线程)可见。如果没有volatile，读者可以看到一些未更新的值。

回答您的问题:是的，我使用一个volatile变量来控制某些代码是否继续循环。循环测试易变值，如果为真则继续。可以通过调用“stop”方法将条件设置为false。循环看到false，并在stop方法完成执行后测试该值时终止。

我强烈推荐的《Java并发实践》一书对volatile做了很好的解释。这本书的作者与问题中提到的IBM文章的作者是同一人(事实上，他在那篇文章的末尾引用了他的书)。我对volatile的使用被他的文章称为“模式1状态标志”。

如果您想了解更多关于volatile在底层是如何工作的，请阅读Java内存模型。如果你想超越这个层次，看看像Hennessy & Patterson这样的优秀计算机体系结构书籍，阅读关于缓存一致性和缓存一致性的内容。

绝对是的。(不仅是Java, c#也是如此。)有时，您需要获取或设置一个值，该值保证是给定平台上的原子操作，例如int或boolean，但不需要线程锁定的开销。volatile关键字允许您确保在读取值时获得的是当前值，而不是在另一个线程上写入时被废弃的缓存值。

每个访问volatile字段的线程在继续之前都会读取它的当前值，而不是(可能)使用缓存的值。

只有成员变量可以是易变的或瞬变的。

The volatile key when used with a variable, will make sure that threads reading this variable will see the same value . Now if you have multiple threads reading and writing to a variable, making the variable volatile will not be enough and data will be corrupted . Image threads have read the same value but each one has done some chages (say incremented a counter) , when writing back to the memory, data integrity is violated . That is why it is necessary to make the varible synchronized (diffrent ways are possible)

如果修改是由一个线程完成的，而其他线程只需要读取这个值，则volatile将是合适的。

是的，我经常使用它——它对多线程代码非常有用。你指的那篇文章很好。不过有两件重要的事情要记住:

You should only use volatile if you completely understand what it does and how it differs to synchronized. In many situations volatile appears, on the surface, to be a simpler more performant alternative to synchronized, when often a better understanding of volatile would make clear that synchronized is the only option that would work. volatile doesn't actually work in a lot of older JVMs, although synchronized does. I remember seeing a document that referenced the various levels of support in different JVMs but unfortunately I can't find it now. Definitely look into it if you're using Java pre 1.5 or if you don't have control over the JVMs that your program will be running on.