并發可能產生的三種問題

臟讀

定義：A事務執行過程中B事務讀取了A事務的修改，但是A事務并沒有結束（提交），A事務后來可能成功也可能失敗。

比喻：A修改了源代碼并且并沒有提交到源代碼系統，A直接通過QQ將代碼發給了B，A后來取消了修改。

代碼示例
代碼如下:
[TestMethod]
         public void 臟讀_測試()
         {
             //前置條件
             using (var context = new TestEntities())
             {
                 Assert.AreEqual(1, context.Tables.Count());
             }

             var autoResetEvent = new AutoResetEvent(false);

             var transactionOptions1 = new TransactionOptions { IsolationLevel = IsolationLevel.ReadCommitted };
             var transactionOptions2 = new TransactionOptions { IsolationLevel = IsolationLevel.ReadUncommitted };

             using (var ts1 = new TransactionScope(TransactionScopeOption.Required, transactionOptions1))
             {
                 //添加數據
                 using (var context = new TestEntities())
                 {
                     context.Tables.Add(new Table() { Id = Guid.NewGuid(), Name = "段光偉" });
                     context.SaveChanges();
                 }

                 ThreadPool.QueueUserWorkItem(data =>
                 {
                     using (var ts2 = new TransactionScope(TransactionScopeOption.Required, transactionOptions2))
                     {