Java 线程不共享静态数据

Question

我有两个线程应该共享静态变量数据（不是常量），它们必须相应地执行。但是这些线程中没有一个能够获取更新后的静态变量数据，除了每个线程都为静态变量维护自己的状态。

我已将静态变量放在单例中并将其声明为 volatile，但结果仍然相同。

有人可以提出这种方法的问题吗？可以采取什么措施来解决这个问题。

谢谢， 阿杰

below is the code

following is the singleton class

***************************************************************************
public class ThreadFinder {

    public static String pageName;//HashMap threadInfo = new HashMap(); //new HashMap();

private static ThreadFinder singletonObject;
/** A private Constructor prevents any other class from instantiating. */
private ThreadFinder () {
    }
public static synchronized ThreadFinder getSingletonObject() {
    if (singletonObject == null) {
        singletonObject = new ThreadFinder();
    }
    return singletonObject;
}
public static synchronized void setPageName(String Name) {

    pageName = Name;
    //return;
}
public static synchronized String getPageName() {

    return pageName;
    //return;
}
public Object clone() throws CloneNotSupportedException {
    throw new CloneNotSupportedException();
}
//public static void main(String args[])
//{
    //ThreadFinder.getSingletonObject().setPageName("IDEN");
    //System.out.println("page name--------->"+ThreadFinder.getSingletonObject().getPageName());
    //ThreadFinder.getSingletonObject().setPageName("THER");
    //System.out.println("page name--------->"+ThreadFinder.getSingletonObject().getPageName());
//}
}

********************************************************************************

from page 1 below code executes and sets the singleton page variable value to "A" and first pollertimer thread uses the page value as A.

m_poller.setModbusMaster(this.m_connection.getModbusMaster());
m_poller.addListener(this);
ThreadFinder.getSingletonObject().setPageName("A");  //Setting the page name here
PollerTimer polerTimerThread = new PollerTimer(period,"A");  // this is thread

*********************************************************************************

from page2 below code executes and sets the singleton page variable value to "B" and second pollertimer thread uses the page value as B.

m_poller.setModbusMaster(this.m_connection.getModbusMaster());
m_poller.addListener(this);
ThreadFinder.getSingletonObject().setPageName("B");  //Setting the page name here
PollerTimer polerTimerThread = new PollerTimer(period,"B");  // this is thread

***********************************************************************************

Now when first pollertimer thread queries page value using getPageName() it is getting value A instead of B, though it was updated to B by the second thread.

Answer 1

如果你打算改变它的状态，那么声明你的引用单例 volatile 不会有帮助。您需要使用由 volatile var 引用的 不可变 单例，或者使该单例中的 每个单独的 var 为 volatile。这只是在你没有原子性问题的情况下。第二种方法与根本没有单例几乎相同，只是一些 static volatile 全局变量。