C# 尝试修改字典时发生异常

我正在创建一个字典来管理线程，当我在字典中添加一些线程后试图清除死线程时，遇到了这个异常

using System;
using System.Collections.Generic;
using System.Threading;

namespace SysCat {
    public class ThreadManager {
        public static readonly ThreadManager GlobalThreadManager = new ThreadManager( );

        /// <summary>
        /// Initializes a new instance of the <see cref="SysCat.ThreadManager"/> class.
        /// </summary>
        public ThreadManager( ) {

        }

        /// <summary>
        /// Create a new ThreadManager with all the Threads within baseTM and deinitializes baseTM
        /// </summary>
        public ThreadManager( ThreadManager baseTM ) {
            this.threads = baseTM.threads;
            baseTM.threads.Clear( );
        }

        private Dictionary<Guid,Thread> threads = new Dictionary<Guid, Thread>( );

        /// <summary>
        /// Attempts to obtain an unused ThreadID within an attempt limit
        /// </summary>
        /// <returns>The unused ThreadID, if found</returns>
        /// <param name="attempts">The number of iterations to try.</param>
        public Guid getUnusedThreadID( int attempts ) {
            lock( threads ) {
                Guid threadID;
                int totalAttempts = attempts;
                while( threads.ContainsKey( ( threadID = Guid.NewGuid( ) ) ) ) {
                    attempts--;
                    if( attempts == 0 )
                        throw new NoOpenThreadIDException( totalAttempts );
                }
                return threadID;
            }
        }

        /// <summary>
        /// Attempts to get a Thread via its ThreadID, if it exists
        /// </summary>
        /// <returns>The Thread</returns>
        /// <param name="threadID">The ThreadID to use</param>
        public Thread getThread( Guid threadID ) {
            lock( threads ) {
                Thread tryGet;
                if( !threads.TryGetValue( threadID, out tryGet ) )
                    throw new ArgumentException( "Specified ThreadID does not exist in this ThreadManager" );
                return tryGet;
            }
        }

        /// <summary>
        /// Attempts to get a ThreadID via the Thread
        /// </summary>
        /// <returns>The ThreadID</returns>
        /// <param name="thread">The Thread to use</param>
        public Guid getThreadID( Thread thread ) {
            lock( threads ) {
                if( threads.ContainsValue( thread ) ) {
                    foreach( Guid id in threads.Keys ) {
                        Thread t;
                        threads.TryGetValue( id, out t );
                        if( t.Equals( thread ) )
                            return id;
                    }
                    // I should never get here
                    return Guid.Empty;
                }
                else
                    throw new ArgumentException( "Specified Thread does not exist in this ThreadManager" );
            }
        }

        /// <summary>
        /// Adds the Thread, unless it cannot find an open ThreadID
        /// </summary>
        /// <returns>The ThreadID used to register the Thread</returns>
        /// <param name="thread">The Thread to register</param>
        public Guid addThread( Thread thread ) {
            lock( threads ) {
                Guid id;
                try {
                    id = getUnusedThreadID( 500 );
                }
                catch( NoOpenThreadIDException e ) {
                    throw e;
                }
                threads.Add( id, thread );
                return id;
            }
        }

        /// <summary>
        /// Attempts to clear all stopped and null Threads
        /// </summary>
        /// <returns>The number of dead Threads cleared</returns>
        public int clearDeadThreads() {
            int cleared = 0;
            lock(threads) {
                foreach( Guid id in threads.Keys ) {
                    Thread thread;
                    threads.TryGetValue( id, out thread );
                    if( thread == null ) {
                        // Does not exist, Thread is dead
                        cleared++;
                        threads.Remove( id );
                        continue;
                    }
                    if( !thread.IsAlive ) {
                        // Not alive, Thread is dead
                        cleared++;
                        threads.Remove( id );
                        continue;
                    }
                }
            }

            return cleared;
        }

        public class NoOpenThreadIDException : Exception {
            public NoOpenThreadIDException( int attempts )
                : base( string.Format( "Unable to find an open ThreadID within the attempt limit of {0}", attempts ) ) {
            }
        }
    }
}

---

在枚举时，不能修改

IEnumerable

你可以做一个简单的破解，获得你正在枚举的内容的副本，这样更改就不会导致

System.InvalidOperationException

例如，而不是

foreach( Guid id in threads.Keys) 

使用

---

请记住，您可以使用

我正在使用lock来同步代码。不过，感谢您向我指出并发部分。在我的方法列表中，我看不到这一点，它是否仅存在于.net的特定版本中？请尝试使用System.Linq添加

。谢谢您的帮助！让我让accept的倒计时结束。
foreach( Guid id in threads.Keys) 

foreach( Guid id in threads.Keys.ToList())