收集被修改;枚举操作可能无法执行.例外
码：
public static string GetValue(List<StateBag> stateBagList,string name)
{
string retValue = string.Empty;
if (stateBagList != null)
{
foreach (StateBag stateBag in stateBagList)
{
if (stateBag.Name.Equals(name,StringComparison.InvariantCultureIgnoreCase))
{
retValue = stateBag.Value;
}
}
}
return retValue;
}
在某个时间点获得此异常并非每次都在这个地方.
堆栈跟踪：
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource
resource)at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at Tavisca.TravelNxt.Shared.Entities.StateBag.GetValue(List`1 stateBagList,String name)
@no我试过以下代码,但仍然有异常
码：
class StateBag
{
public string Name;
public string Value;
}
class Program
{
static List<StateBag> _concurrent = new List<StateBag>();
static void Main()
{
var sw = new Stopwatch();
try
{
sw.Start();
Thread thread1 = new Thread(new ThreadStart(A));
Thread thread2 = new Thread(new ThreadStart(B));
thread1.Start();
thread2.Start();
thread1.Join();
thread2.Join();
sw.Stop();
}
catch (Exception ex)
{
}
Console.WriteLine("Average: {0}",sw.ElapsedTicks);
Console.ReadKey();
}
private static Object thisLock = new Object();
public static string GetValue(List<StateBag> stateBagList,string name)
{
string retValue = string.Empty;
if (stateBagList != null)
{
lock (thisLock)
{
foreach (StateBag stateBag in stateBagList)
{
if (stateBag.Name.Equals(name,StringComparison.InvariantCultureIgnoreCase))
{
retValue = stateBag.Value;
}
}
}
}
return retValue;
}
static void A()
{
for (int i = 0; i < 5000; i++)
{
_concurrent.Add(new StateBag() { Name = "name" + i,Value = i.ToString() });
}
}
static void B()
{
for (int i = 0; i < 5000; i++)
{
var t = GetValue(_concurrent,"name" + i);
}
}
}
解决方法
Getting Collection was modified; enumeration operation may not execute. exception
原因：当您循环的枚举在同一个线程或其他某个线程中被修改时,会发生此异常.
现在,在您提供的代码中,没有任何此类方案.这意味着您可能在多线程环境中调用它,并且在其他一些线程中修改了集合.
解决方案：在枚举上实现锁定,以便一次只能访问一个线程.这样的事情应该做到这一点.
private static Object thisLock = new Object();
public static string GetValue(List<StateBag> stateBagList,string name)
{
string retValue = string.Empty;
if (stateBagList != null)
{
lock(thisLock)
{
foreach (StateBag stateBag in stateBagList)
{
if (stateBag.Name.Equals(name,StringComparison.InvariantCultureIgnoreCase))
{
retValue = stateBag.Value;
}
}
}
}
return retValue;
}
