多線程中訪問public List<Entity> Entities { get { lock(syncObjecct){return ....}} set{ lock(syncObject){....}}; Entities對象時，為什么循環遍歷時有時候會發生錯誤（Note: 我已經加鎖對象并且用for循環而不是foreach循環訪問對象）。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(){//多個線程添加刪除訪問Entities鏈表時候遍歷有時會發生錯誤for (int i = 0; i <Entities.Count;i++) {var item = Entities[0]; //報錯：集合已經被修改 }}
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慕無忌1623718
TA貢獻1744條經驗 獲得超4個贊
）【異常的原因】
按您給出的代碼，問題出在public List<Entity> Entities{get; set;}上：這個屬性方法在獲取List<Entity>實例的執行過程中利用了lock(){}來保持同步；但是，一旦這個屬性方法執行結束就跳出了lock(){}的同步范圍。這意味著：在主函數中所獲取的List<Entity>實例已經不再受到lock的保護了！遍歷集合發生將拋出異常（通常是“集合序數變化……”之類的異常）
2）【解決方法】
關鍵是為遍歷集合的方法提供同步功能。見下面的代碼
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) { //啟動線程：向集合中添加 Thread threadAdding = new Thread(Adding); threadAdding.IsBackground = true; threadAdding.Start(); //啟動線程：從集合中刪除 Thread threadRemoving = new Thread(Removing); threadRemoving.IsBackground = true; threadRemoving.Start(); //啟動線程：遍歷集合 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) { //遍歷集合 foreach (var e in list) { Console.WriteLine(e.ToString()); } Console.WriteLine("------------"); Thread.Sleep(1000); } } } /// <summary> /// 實體對象 /// </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> /// 實體對象列表（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); } } //帶同步功能的集合遍歷接口 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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