使用线程安全的 ConcurrentDictionary 集合

Question

我有一个这样的函数，它使用非线程安全的集合列表，也是线程安全的，它使用锁操作符：

public void ShowData(ref DataGridView dmRequests, ref DataGridView URL, ref DataGridView dmData, ref DataGridView errorCodes)
{
    List<KeyValuePair<string, ulong>> dmReqList = new List<KeyValuePair<string, ulong>>();
    List<KeyValuePair<string, ulong>> urlReqList = new List<KeyValuePair<string, ulong>>(); 
    List<KeyValuePair<string, ulong>> dmDataList = new List<KeyValuePair<string, ulong>>();
    List<KeyValuePair<string, ulong>> errCodesList = new List<KeyValuePair<string, ulong>>();

    lock (m_logStruct.domainName)
    {
        dmReqList = m_logStruct.domainName.ToList();
    }
    lock(m_logStruct.URL)
    {
        urlReqList = m_logStruct.URL.ToList();
    }
    lock(m_logStruct.domainData)
    {
        dmDataList = m_logStruct.domainData.ToList();
    }
    lock(m_logStruct.errorCodes)
    {
        errCodesList = m_logStruct.errorCodes.ToList();
    }

    dmRequests.DataSource = dmReqList.OrderBy(x => x.Key).ToList();
    URL.DataSource = urlReqList.OrderBy(x => x.Key).ToList();
    dmData.DataSource = dmDataList.OrderBy(x => x.Key).ToList();
    errorCodes.DataSource = errCodesList.OrderBy(x => x.Key).ToList();
}

我想将其转换为无锁。为此，我在这个函数中使用了 ConcurrentDictionary 集合而不是 List 集合，所以我的函数开始看起来是这样的：

public void ShowData(ref DataGridView dmRequests, ref DataGridView URL, ref DataGridView dmData, ref DataGridView errorCodes)
{
    try
    {
        ConcurrentDictionary<string, ulong> dmReqList = new ConcurrentDictionary<string, ulong>();
        ConcurrentDictionary<string, ulong> urlReqList = new ConcurrentDictionary<string, ulong>();
        ConcurrentDictionary<string, ulong> dmDataList = new ConcurrentDictionary<string, ulong>();
        ConcurrentDictionary<string, ulong> errCodesList = new ConcurrentDictionary<string, ulong>();

        dmReqList = m_logStruct.domainName;
        urlReqList = m_logStruct.URL;
        dmDataList = m_logStruct.domainData;
        errCodesList = m_logStruct.errorCodes;

        dmRequests.DataSource = dmReqList.OrderBy(x => x.Key);
        URL.DataSource = urlReqList.OrderBy(x => x.Key).ToList();//I get error here: Index is out of range                
        dmData.DataSource = dmDataList.OrderBy(x => x.Key).ToList();              
        errorCodes.DataSource = errCodesList.OrderBy(x => x.Key).ToList();
    }
    catch(IOException e)
    {
        MessageBox.Show(e + " Something bad has been occurred here!");
    }

}

但是在这个函数中我开始得到错误（索引超出范围）。如何正确使用线程安全集合（ConcurrentDictionary）？如何解决我的错误？

Answer 1

如果您要替换存储列表的变量，它不会是并发的。您需要使用它提供的并发方法。请参阅MSDN article 中的示例。

使用TryAdd、TryUpdate、TryRemove 或AddOrUpdate 来添加到列表或更新列表，而不是：

dmReqList = m_logStruct.domainName;

执行以下操作：

foreach (var item in m_logStruct.domainName)
{
    dmReqList.TryAdd(item.Key, item.Value);
}

更新： 正如 Alexei 所指出的，您正在本地定义 dmReqList。这意味着您不会从它作为 ConcurrentDictionary 中获得任何好处，因为无论如何其他线程都无法访问它。此外，您从原始示例中暗示 m_logStruct 可以通过其他线程访问，因为您对其应用了锁。如果暗示是正确的，那么这就是需要成为 ConcurrentDictionary 的内容。因此，您的代码需要看起来更像这样：

private ConcurrentDictionary<string, ulong> _domainNames = new ConcurrentDictionary<string, ulong>();

public void ShowData(ref DataGridView dmRequests)
{
    dmRequests.DataSource = _domainNames.OrderBy(x => x.Key);  //Set the current values of the dictionary to the grid.
}

public void MultiThreadedMethod()
{
    _domainNames.TryAdd(someKey, someValue);  //Access the dictionary from multiple threads.
}