如何解决此内存一致性错误？

Question

我有一个多线程 Java 程序出现内存一致性错误。我天真地试图通过声明我所有的变量 volatile 和同步方法来解决这个问题，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。这是真实世界的输出：

<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 设置为与线程 13 设置的值相同的值。不过那是错误的，不知何故，正确的值赶上了。把这个小代码sn-p做起来很难，所以我会尽量准确描述代码序列，同时保持简短。

编辑：我修改了每个请求的代码（原始代码太短）

这段代码仍然缺少一些东西。我不能包含它，因为它允许您连接到 TDAmeritrade 的 API 服务器。如果这样会更好，我可以创建随机生成的日期吗？我知道这不会为你编译。我仍在学习该站点的协议。让我知道这是否有误。

此外，当我将其作为单线程运行时，它可以工作。没有内存错误。所以，肯定是多线程。此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。它没有帮助。

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解决它，我会非常喜欢它？

Answer 1

我认为问题只是Root.getHelp().getSdfYearMonthDay() 正在返回一个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")

并查看问题是否仍然存在。我敢打赌它已经消失了。