为什么循环遍历时有时候会发生错误呢？怎么解决？
多线程中访问public List<Entity> Entities { get { lock(syncObjecct){return ....}} set{ lock(syncObject){....}}; Entities对象时，为什么循环遍历时有时候会发生错误（Note: 我已经加锁对象并且用for循环而不是foreach循环访问对象）。
我的程序：
private List<Entity> entities = new List<Entities>();
public List<Entity> Entities { get { lock(syncObjecct){return ...entities.}} set{ lock(syncObject){....entities = value}};
private void Insert(Entity entity)
{
Entities.add(entity);
}
private void Remove()
{
if (Entityes.Count >0 )
Entities.Remove(0);
}
int main()
{
//多个线程添加删除访问Entities链表时候遍历有时会发生错误
for (int i = 0; i <Entities.Count;i++)
{
var item = Entities[0]; //报错：集合已经被修改
}
}
芜湖不芜浏览 88回答 1
1回答
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慕无忌1623718
）【异常的原因】按您给出的代码，问题出在public List<Entity> Entities{get; set;}上：这个属性方法在获取List<Entity>实例的执行过程中利用了lock(){}来保持同步；但是，一旦这个属性方法执行结束就跳出了lock(){}的同步范围。这意味着：在主函数中所获取的List<Entity>实例已经不再受到lock的保护了！遍历集合发生将抛出异常（通常是“集合序数变化……”之类的异常）2）【解决方法】关键是为遍历集合的方法提供同步功能。见下面的代码using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Threading; namespace ConsoleApplication1{ class Program { static EntityList list = new EntityList(); static void Main(string[] args) { //启动线程：向集合中添加 Thread threadAdding = new Thread(Adding); threadAdding.IsBackground = true; threadAdding.Start(); //启动线程：从集合中删除 Thread threadRemoving = new Thread(Removing); threadRemoving.IsBackground = true; threadRemoving.Start(); //启动线程：遍历集合 Thread threadWork = new Thread(Work); threadWork.IsBackground = true; threadWork.Start(); Console.ReadKey(); } static void Adding() { int id = 0; while (true) { id++; list.Insert(new Entity() { Id = id, Gender = "Male", Name = "Someone" + id.ToString() }); Thread.Sleep(750); } } static void Removing() { while (true) { list.Remove(); Thread.Sleep(1000); } } static void Work() { while (true) { //遍历集合 foreach (var e in list) { Console.WriteLine(e.ToString()); } Console.WriteLine("------------"); Thread.Sleep(1000); } } } /// <summary> /// 实体对象 /// </summary> class Entity { public int Id { get; set; } public string Name { get; set; } public string Gender { get; set; } public override string ToString() { return string.Format( "Id={0} Name={1} Gender={2}", Id, Name, Gender ); } } /// <summary> /// 实体对象列表（集合） /// </summary> class EntityList : IEnumerable<Entity> { object syncObject = new object(); List<Entity> list = new List<Entity>(); public void Insert(Entity entity) { lock (syncObject) { list.Add(entity); } } public void Remove() { lock (syncObject) { if (list.Count > 0) list.RemoveAt(0); } } //带同步功能的集合遍历接口 public IEnumerator<Entity> GetEnumerator() { lock (syncObject) { foreach (var v in list) { yield return v; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { return this.GetEnumerator(); } }}
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