無法使用線程和XDocument寫入XML文件

Question

string filepath = Environment.CurrentDirectory + @"Expense.xml";

public void  WriteToXML(object param)
{
Expense exp = (Expense)param;
   if (File.Exists(filepath)) {
    XDocument xDocument = XDocument.Load(filepath);

    XElement root = xDocument.Element("Expenses");
    IEnumerable<XElement> rows = root.Descendants("Expense");
    XElement firstRow = rows.First();

    firstRow.AddBeforeSelf(new XElement("Expense",
           new XElement("Id", exp.Id.ToString()),
           new XElement("Amount", exp.Amount.ToString()),
           new XElement("Contact", exp.Contact),
           new XElement("Description", exp.Description),
           new XElement("Datetime", exp.Datetime)));
    xDocument.Save(filepath);
 }
}

Expense exp = new Expense();
exp.Id = new Random().Next(1, 10000);
exp.Amount = float.Parse(text1[count].Text);
exp.Contact = combo1[count].SelectedItem.ToString();
exp.Description = rtext1[count].Text.ToString();
exp.Datetime = DateTime.Now.ToString("MM-dd-yyyy");

workerThread = new Thread(newParameterizedThreadStart(WriteToXML));
workerThread.Start(exp); // throws System.IO.IOException

我無法使用輔助程序寫入XML文件-我收到此錯誤：

System.IO.IOException：'該進程無法訪問文件'C：\\ work \\ FinanceManagement \\ FinanceManagement \\ bin \\ DebugExpense.xml'，因為該文件正在被另一個進程使用。

但是如果我像WriteToXML(exp);一樣使用它WriteToXML(exp); 有用。 我認為XDocument.Load(filepath)不是線程安全的。 我該如何解決這個問題？

Answer 1

嘗試引入lock ，看看它是否可以解決問題：

// Declare this somewhere in your project, can be in same class as WriteToXML
static object XmlLocker;

然后在邏輯周圍包裹一個lock ：

public void WriteToXML(object param)
{
    Expense exp = (Expense)param;

    lock (XmlLocker) // <-- this limits one thread at a time
    {
        if (File.Exists(filepath))
        {
            XDocument xDocument = XDocument.Load(filepath);

            XElement root = xDocument.Element("Expenses");
            IEnumerable<XElement> rows = root.Descendants("Expense");
            XElement firstRow = rows.First();

            firstRow.AddBeforeSelf(new XElement("Expense",
                   new XElement("Id", exp.Id.ToString()),
                   new XElement("Amount", exp.Amount.ToString()),
                   new XElement("Contact", exp.Contact),
                   new XElement("Description", exp.Description),
                   new XElement("Datetime", exp.Datetime)));
            xDocument.Save(filepath);
        }
    }
}