如何解决此内存一致性错误?

Question

我有一个多线程Java程序，它正在获得内存一致性错误。我曾经天真地试图通过声明我所有的变量为volatile和方法为synchronized来解决这个问题，但这并没有奏效。

有时，前一个对象的内存会出现在其他新对象中。以下是真实世界的输出:

<Thread-13> OptionRow (AMGN_062714P116) expDate set to 2014-06-27
Thread-9 2) OFT-Thread (AIG_052314C50) populateTable expDate = 2014-06-27 year=2014 month=5 day=23
<Thread-9> OptionRow (AIG_052314C50) expDate set to 2014-05-23

您可以看到线程9将expDate设置为线程13设置的相同值。虽然这是错误的，但不知何故，正确的值赶上了。很难把这段代码做成一个小代码片段，所以我将尽可能准确地描述代码序列，同时保持它的简短。

edit:我根据请求修改了代码(原始代码太短)

这段代码中仍然缺少一些东西。我不能包含它，因为它将允许您连接到TDAmeritrade的API服务器。我可以创建随机生成的日期，这样更好吗?我知道这不会为你编译。我还在学习这个网站的协议。如果这是错误的，请告诉我。

另外，当我将其作为单个线程运行时，它工作了。没有内存错误。所以，这绝对是多线程。这个版本与我最初发布的版本不同。我希望使用ExecutorService线程池会有所帮助。没用的。

import java.util.Iterator;
import java.util.TreeSet;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import broker.Root;
import java.util.ArrayList;
import java.util.GregorianCalendar;
import networking.ParseBinaryOptionChain;
public class StackOverflowCode {
    public StackOverflowCode () {
        Root root = new Root();
        MyStatement myStatement = new MyStatement (root);
        root.setStatement(myStatement);
        networking.TDAConnection tdaConn = new networking.TDAConnection(root);
        tdaConn.login();
        root.setTDAConnection(tdaConn);
        Table table = new Table(root);
        new Thread(table).start();        
    }
    public static void main(String[] args){
        new StackOverflowCode();
    }
}
class Table implements Runnable {
    Root root;
    private ArrayList <OptionRow> optionList;
    public Table(Root r){
        // guess initial list size is 125,000 symbols
        optionList = new ArrayList<>(125000); 
        root = r;
    }
    @Override
    public void run() {
        getUnderlyingList(); 
    }
    public void addAll(ArrayList options) {
        optionList.addAll(options);
    }
    private void getUnderlyingList() {
        try {
            final TreeSet dbStocks = (TreeSet) root.getMyStatement().getStockSymbolsFromOptionsFilterDatabase();
            ExecutorService pool = Executors.newFixedThreadPool(10);
            String stock = null;
            for (Iterator it = dbStocks.iterator(); it.hasNext(); stock = (String) it.next()) {
                pool.submit(new Download(root, stock, this));
            }
            pool.shutdown();
            pool.awaitTermination(Long.MAX_VALUE, TimeUnit.MILLISECONDS);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
}
class Download implements Runnable {
    private String stock;
    private Root root;
    private Table parent;
    public Download(Root root, String stock, Table parent) {
        this.root = root;
        this.stock = stock;
        this.parent = parent;
    }
    @Override
    public void run() {
        PopulateTable pop = new PopulateTable(root, stock, parent);
        pop.populateTable();
    }
}
class PopulateTable {
    private String stockSymbol;
    private Root root;
    private Table parent;
    private ArrayList <OptionRow> optionList;
    private ParseBinaryOptionChain pBOC;
    private volatile OptionRow option;
    private volatile GregorianCalendar expDate;
    public PopulateTable(Root root, String stockSymbol, Table parent) {
        this.root = root;
        this.stockSymbol = stockSymbol;
        this.parent = parent;
        optionList = new ArrayList<>();
    }
    public synchronized void populateTable() {
        try {
            // Download all the options associated with the stock symbol
            // and parse them directly from the Internet.
            pBOC = root.getTDAConnection().requestBinaryOptionChain(stockSymbol);
            root.getMyStatement().setLastStockPrice(stockSymbol, pBOC.getsLast());
            root.getMyStatement().setCompanyName(stockSymbol, new networking.YahooConnect(root).symbolLookup(stockSymbol));
            // Here's where we will be going through each option. Collect the info
            // we are interested in here. Put the info in the options table. 
            while (pBOC.next()&&root.buttonIsOnline()){ 
                boolean isCall = false;
                if (pBOC.getPutCallIndicator()=='C') 
                    isCall = true;
                String date = pBOC.getODate();
                expDate = new GregorianCalendar (
                        Integer.parseInt(date.substring(0, 4)),
                        (Integer.parseInt(date.substring(4, 6))-1),
                        Integer.parseInt(date.substring(6, 8)));
                System.out.println ("<"+Thread.currentThread().getName()+"> ("+pBOC.getOSymbol()+") populateTable expDate = "
                        +root.getHelp().getSdfYearMonthDay().format(expDate.getTime())
                        +" year="+Integer.parseInt(date.substring(0, 4))
                        +" month="+Integer.parseInt(date.substring(4, 6))
                        +" day="+ Integer.parseInt(date.substring(6, 8)));
                System.out.println (Thread.currentThread().getName()+" 2) OFT-Thread ("+pBOC.getOSymbol()+") populateTable expDate = "
                        +root.getHelp().getSdfYearMonthDay().format(expDate.getTime())
                        +" year="+Integer.parseInt(date.substring(0, 4))
                        +" month="+Integer.parseInt(date.substring(4, 6))
                        +" day="+ Integer.parseInt(date.substring(6, 8)));
                option = new OptionRow(root, expDate, new GregorianCalendar());
                optionList.add(option);
            }
            // add all the options to the parent table
            parent.addAll(optionList);
            // Saves all the downloaded info to the database
            root.getMyStatement().insertOptionsInfoForFilter(optionList);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}
class OptionRow {
   private Root root;
   private volatile GregorianCalendar expDate;
   public OptionRow (Root root, GregorianCalendar expDate, Object... o) {
       this.root = root;
       this.expDate = expDate;
   }
}

如果有人能告诉我为什么会发生错误以及如何修复它，我真的很喜欢它?

Answer 1

我认为问题很简单，Root.getHelp().getSdfYearMonthDay()返回共享日期格式化程序。这些对象不是线程安全的，通常，共享这些对象会导致格式化另一个线程的日期。

代替

root.getHelp().getSdfYearMonthDay()

替换为:

new SimpleDateFormat("yyyy-MM-dd")

看看问题是否仍然存在。