C#多线程共享变量循环遍历

Question

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 }}