InvalidOperationException：集合已修改-尽管锁定了集合 [英] InvalidOperationException: Collection was modified - although locking the collection

问题描述

我有一个同步的哈希表，我会定期从中删除一些条目。多个线程运行此代码。所以我锁定了整个foreach，但有时仍然会收到InvalidOperationException：在Hashtable.HashtableEnumerator.MoveNext（）处修改了collection-即在foreach循环中。
我在做什么错？

I have a synchronized hashtable, from which I regularly remove some entries. Multiple threads run this code. So I lock the entire foreach, but I still sometimes get InvalidOperationException: Collection was modified ... at Hashtable.HashtableEnumerator.MoveNext() - i.e. in the foreach loop. What am I doing wrong? Isn't locking enough?

private static readonly Hashtable sessionsTimeoutData = Hashtable.Synchronized(new Hashtable(5000));

私有静态无效ClearTimedoutSessions（）
{
List keysToRemove = new List（）;现在，
长= DateTime.Now.Ticks;
锁定（sessionsTimeoutData）
{
TimeoutData timeoutData;
foreach（sessionTimeoutData中的DictionaryEntry条目）
{
timeoutData =（TimeoutData）entry.Value;
if（现在-timeoutData.LastAccessTime> timeoutData.UserTimeoutTicks）
keysToRemove.Add（（ulong）entry.Key）;
}
}
foreach（keyToToMove中的长键）
sessionsTimeoutData.Remove（key）;
}

private static void ClearTimedoutSessions() { List keysToRemove = new List(); long now = DateTime.Now.Ticks; lock (sessionsTimeoutData) { TimeoutData timeoutData; foreach (DictionaryEntry entry in sessionsTimeoutData) { timeoutData = (TimeoutData)entry.Value; if (now - timeoutData.LastAccessTime > timeoutData.UserTimeoutTicks) keysToRemove.Add((ulong)entry.Key); } } foreach (ulong key in keysToRemove) sessionsTimeoutData.Remove(key); }

推荐答案

您要使用 SyncRoot 是同步的 Hashtable 的方法将锁定的对象：

You want to lock using SyncRoot which is the object that the methods for a synchronized Hashtable will lock on:

lock (sessionsTimeoutData.SyncRoot)
{
    // ...
}

请参见 http://msdn.microsoft.com/zh-cn/library/system.collections.hashtable.synchronized.aspx ：

通过集合进行枚举本质上不是线程安全的
过程。即使集合同步
，其他线程仍可以
修改该集合，这会导致
枚举器抛出异常。
为了保证
枚举期间的线程安全，您可以在整个
枚举期间锁定
集合，也可以捕获其他$ b $所做的更改导致的异常

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

以下代码示例显示
如何在整个
枚举期间使用
SyncRoot锁定集合：

The following code example shows how to lock the collection using the SyncRoot during the entire enumeration:

Hashtable myCollection = new Hashtable();
lock(myCollection.SyncRoot)
{
    foreach (object item in myCollection)
    {
        // Insert your code here.
    }
}

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