.net 异步套接字超时检查线程安全答案

【问题标题】：.net async socket timeout check thread-safety.net 异步套接字超时检查线程安全
【发布时间】：2010-11-16 22:31:09
【问题描述】：

http://msdn.microsoft.com/en-us/library/system.net.sockets.socketasynceventargs.aspx

从上面的 msdn 示例开始，我正在尝试编写一个超时检查，它将关闭不活动的客户端套接字并释放资源。

这是我想出的。但我不确定它是否完全线程安全以及是否有更好的方法来做到这一点。希望有人能给点建议。

void IO_Completed(object sender, SocketAsyncEventArgs e)
{
    if (e.SocketError != SocketError.Success)
    {
        CloseClientSocket(e);
        return;
    }

    if (1 < Interlocked.CompareExchange(ref token.Status, 1, 0))
        return;

    switch (e.LastOperation)
    {
        case SocketAsyncOperation.Receive:
            ProcessReceive(e);
            break;
        ...
    }

    token.LastActive = Environment.TickCount;
    Interlocked.CompareExchange(ref token.Status, 0, 1);
}

void ProcessReceive(SocketAsyncEventArgs e)
{
    AsyncUserToken token = (AsyncUserToken)e.UserToken;
    if (e.BytesTransferred > 0)
        if (!token.Socket.SendAsync(e))
            ProcessSend(e);
    else
        CloseClientSocket(e);
}

void ProcessSend(SocketAsyncEventArgs e)
{
    AsyncUserToken token = (AsyncUserToken)e.UserToken;
    if (!token.Socket.ReceiveAsync(e))
        ProcessReceive(e);
}

TimeoutCheck 将每 20 秒执行一次。 allReadWriteArgs 是一个包含所有 SocketAsyncEventArgs 的数组。关闭套接字后，将使用 SocketError.OperationAborted 调用 IO_Completed。

void TimeoutCheck(object state)
{
    AsyncUserToken token;
    int timeout = Environment.TickCount - 20000;
    for (int i = 0; i < allReadWriteArgs.Length; i++)
    {
        token = (AsyncUserToken)allReadWriteArgs[i].UserToken;
        if (token.LastActive < timeout)
            if (0 == Interlocked.CompareExchange(ref token.Status, 2, 0))
                Interlocked.Exchange(ref token.Socket, null).Close();
    }
}


void CloseClientSocket(SocketAsyncEventArgs e)
{
    AsyncUserToken token = e.UserToken as AsyncUserToken;

    if (token.Socket != null)
    {
        try
        {
            token.Socket.Shutdown(SocketShutdown.Both);
        }
        catch (SocketException) { }
        token.Socket.Close();
    }

    token.Status = 2;
    bufferManager.FreeBuffer(e);
    readWritePool.Push(e);
    ...
}

【问题讨论】：

这有点老了，但对于以后阅读它的人来说：不要在应用程序中使用Environment.TickCount 进行任何计算。它表示为Int32，它将在 24.9 天内用完并循环到负整数并最终返回 0。请改用DateTime.UtcNow.Ticks。

标签： c# multithreading asynchronous sockets timeout

【解决方案1】：

您的代码看起来不错。你也可以这样做：

void _connectionActivityCheck_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    _connectionActivityCheck.Stop();

    try
    {
        List<Guid> connectionsToRemove = new List<Guid>();

        lock (_connections.SyncRoot)
        {
            IncomingConnection conn;

            foreach (DictionaryEntry item in _connections)
            {
                conn = (IncomingConnection)item.Value;

                if (conn.LastIncomingActivity.HasValue && 
                    DateTime.Now.Subtract(conn.LastIncomingActivity.Value).TotalSeconds > MaximumInactivitySeconds)
                        connectionsToRemove.Add(conn.ConnectionId);
            }
        }

        if (connectionsToRemove.Count > 0)
        {
            int itemsToRemove = connectionsToRemove.Count;

            foreach (Guid item in connectionsToRemove)
            {
                RemoveConnection(item);
            }

            Context.Current.Logger.LogInfo(_loggerName, 
                string.Format("{0} connections were closed due to incoming traffic inactivity", itemsToRemove));
        }
    }
    catch (Exception ex)
    {
        Context.Current.Logger.LogFatal(_loggerName, "An error ocurred while checking incoming traffic.", ex);
    }
    finally
    {
        _connectionActivityCheck.Start();
    }
}



private void RemoveConnection(Guid connectionId)
{
    lock (_connections.SyncRoot)
    {
        try
        {
            IncomingConnection conn = _connections[connectionId] as IncomingConnection;

            if (conn != null)
            {
                try
                {
                    conn.Dispose();
                }
                catch { }

                _connections.Remove(connectionId);
            }
        }
        catch { }
    }
}

【讨论】：