一、Session Management Service的实现
现在我们来看看Session Management真正的实现，和我以前的例子不同，我不是把所有的实现都写在WCF service上，而是定义了另一个class来实现所有的业务逻辑：SessionManager。我们分析一下具体的实现逻辑。
代码语言：javascript复制1: namespace Artech.SessionManagement.Service
2: {
3: public static class SessionManager
4: {
5: private static object _syncHelper = new object();
6:
7: internal static TimeSpan Timeout
8: { get; set; }
9:
10: public static IDictionary<Guid, SessionInfo> CurrentSessionList
11: { get; set; }
12:
13: public static IDictionary<Guid, ISessionCallback> CurrentCallbackList
14: { get; set; }
15:
16: static SessionManager()
17: {
18: string sessionTimeout = ConfigurationManager.AppSettings["SessionTimeout"];
19: if (string.IsNullOrEmpty(sessionTimeout))
20: {
21: throw new ConfigurationErrorsException("The session timeout application setting is missing");
22: }
23:
24: double timeoutMinute;
25: if (!double.TryParse(sessionTimeout, out timeoutMinute))
26: {
27: throw new ConfigurationErrorsException("The session timeout application setting should be of doubdle type.");
28: }
29:
30: Timeout = new TimeSpan(0, 0, (int)(timeoutMinute * 60));
31: CurrentSessionList = new Dictionary<Guid, SessionInfo>();
32: CurrentCallbackList = new Dictionary<Guid, ISessionCallback>();
33: }
34: //...
35: }
36: }
37:首先来看Field、Property和static constructor的定义。_syncHelper 用于实现多线程同步之用；Timeout是session timeout的时间，可配置；CurrentSessionList和CurrentCallbackList两个dictionary在上面我们已经作过介绍，分别代表当前活动的session列表和callback列表，key均为SessionID。在静态构造函数中，初始化session timeout的时间，和实例化CurrentSessionList和CurrentCallbackList。
接着我们来看看StartSession和EndSession两个方法，这两个方法分别代表Session的开始和结束。
代码语言：javascript复制1: public static Guid StartSession(SessionClientInfo clientInfo)
2: {
3: Guid sessionID = Guid.NewGuid();
4: ISessionCallback callback = OperationContext.Current.GetCallbackChannel<ISessionCallback>();
5: SessionInfo sesionInfo = new SessionInfo() { SessionID = sessionID, StartTime = DateTime.Now, LastActivityTime = DateTime.Now, ClientInfo = clientInfo };
6: lock (_syncHelper)
7: {
8: CurrentSessionList.Add(sessionID, sesionInfo);
9: CurrentCallbackList.Add(sessionID, callback);
10: }
11: return sessionID;
12: }
13:
14: public static void EndSession(Guid sessionID)
15: {
16: if (!CurrentSessionList.ContainsKey(sessionID))
17: {
18: return;
19: }
20:
21: lock (_syncHelper)
22: {
23: CurrentCallbackList.Remove(sessionID);
24: CurrentSessionList.Remove(sessionID);
25: }
26: }在StartSession方法中，首先创建一个GUID作为SessionID。通过OperationContext.Current获得callback对象，并根据client端传入的SessionClientInfo 对象创建SessionInfo 对象，最后将callback对象和SessionInfo 对象加入CurrentCallbackList和CurrentSessionList中。由于这两个集合会在多线程的环境下频繁地被访问，所以在对该集合进行添加和删除操作时保持线程同是显得尤为重要，所在在本例中，所有对列表进行添加和删除操作都需要获得_syncHelper加锁下才能执行。与StartSession相对地，EndSession方法仅仅是将SessionID标识的callback对象和SessionInfo 对象从列表中移除。
然后我们来看看如何强行中止掉一个或多个活动的session：KillSessions。
代码语言：javascript复制1: public static void KillSessions(IList<Guid> sessionIDs)
2: {
3: lock (_syncHelper)
4: {
5: foreach (Guid sessionID in sessionIDs)
6: {
7: if (!CurrentSessionList.ContainsKey(sessionID))
8: {
9: continue;
10: }
11:
12: SessionInfo sessionInfo = CurrentSessionList[sessionID];
13: CurrentSessionList.Remove(sessionID);
14: CurrentCallbackList[sessionID].OnSessionKilled(sessionInfo);
15: CurrentCallbackList.Remove(sessionID);
16: }
17: }
18: }逻辑很简单，就是先从CurrentSessionList中获得对应的SessionInfo 对象，然后将其从CurrentSessionList中移除，然后根据SessionID获得对用的Callback对象，调用OnSessionKilled方法实时通知client session被强行中止，最后将callback对象从CurrentCallbackList中清楚。需要注意的是OnSessionKilled是One-way方式调用的，所以是异步的，时间的消耗可以忽略不计，也不会抛出异常，所以对_syncHelper的锁会很开释放，所以不会对并发造成太大的影响。
Session的管理最终要、也是作复杂的事对Timeout的实现，再我们的例子中，我们通过定期对CurrentSessionList中的每个session进行轮询实现。每次轮询通过RenewSessions方法实现，我们来看看该方法的定义：
代码语言：javascript复制1: [MethodImpl(MethodImplOptions.Synchronized)]
2: public static void RenewSessions()
3: {
4: IList<WaitHandle> waitHandleList = new List<WaitHandle>();
5:
6: foreach (var session in CurrentSessionList)
7: {
8: RenewSession renewsession = delegate(KeyValuePair<Guid, SessionInfo> sessionInfo)
9: {
10: if (DateTime.Now - sessionInfo.Value.LastActivityTime < Timeout)
11: {
12: return;
13: }
14: try
15: {
16: TimeSpan renewDuration = CurrentCallbackList[sessionInfo.Key].Renew();
17: if (renewDuration.TotalSeconds > 0)
18: {
19: sessionInfo.Value.LastActivityTime = renewDuration;
20: }
21: else
22: {
23: sessionInfo.Value.IsTimeout = true;
24: CurrentCallbackList[session.Key].OnSessionTimeout(sessionInfo.Value);
25: }
26: }
27: catch (CommunicationObjectAbortedException)
28: {
29: sessionInfo.Value.IsTimeout = true;
30: return;
31: }
32: };
33:
34: IAsyncResult result = renewsession.BeginInvoke(session, null, null);
35: waitHandleList.Add(result.AsyncWaitHandle);
36: }
37:
38: if (waitHandleList.Count == 0)
39: {
40: return;
41: }
42: WaitHandle.WaitAll(waitHandleList.ToArray<WaitHandle>());
43: ClearSessions();
44: }
45:
46: public delegate void RenewSession(KeyValuePair<Guid, SessionInfo> session);
47:首先我定义了一个delegate：RenewSession，来实现表示对单个session的renew操作。在RenewSessions方法中，我们遍历CurrentSessionList中的每个SessionInfo对象，根据LastActivityTime判断是否需要对该Session进行Renew操作（DateTime.Now - sessionInfo.Value.LastActivityTime < Timeout，意味着单单从server来看，Session都尚未过期），如何需要，则通过SessionID从CurrentCallbackList中取出callback对象，调用Renew方法。如何返回的的Timespan大于零，则表明，client端需要延长session的生命周期，则让LastActivityTime 加上该值。如何返回的值小于零，表明session真的过期了，那么通过调用callback对象的OnSessionTimeout方法实现对client的实时的通知，并将SessionInfo对象的IsTimeout 设置为true。等所以得操作结束之后，在将IsTimeout 为true的SessionInfo对象和对应的callback对象从列表中移除。
在这里有3点需要注意：
1）由于在client过多的情况下，CurrentSessionList得数量太多，按照同步的方式逐个进行状态的检测、callback的调用可以需要很长的时间，会严重影响实时性。所以我们采用的是异步的方式，这是通过将操作定义到RenewSession delegate中，并掉用BeginInvoke方法实现的。
2）在调用Callback的Renew方法的时候，很有可以client端的程序已经正常或者非正常关闭，在这种情况下会抛出CommunicationObjectAbortedException异常，我们应该把这种情况视为timeout。所以我们也将IsTimeout 设置为true。
3）我们之所以现在遍历之后才对session进行清理，主要考虑到我们的操作时在对线程环境中执行，如何在并发操作的情况下对集合进行删除，会出现一些意想不到的不同步情况下。我们通过WaitHandle保证所有的并发操作都结束了：我先创建了一个IList<WaitHandle>对象waitHandleList ，将每个基于session对象的异步操作的WaitHandle添加到该列表（waitHandleList.Add(result.AsyncWaitHandle);）通过
WaitHandle.WaitAll(waitHandleList.ToArray<WaitHandle>());保证所有的操作都结束了。
有了SessionManager，我们的Service就显得很简单了：
代码语言：javascript复制1: namespace Artech.SessionManagement.Service
2: {
3: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode =ConcurrencyMode.Multiple)]
4: public class SessionManagementService:ISessionManagement
5: {
6: #region ISessionManagement Members
7:
8: public Guid StartSession(SessionClientInfo clientInfo,out TimeSpan timeout)
9: {
10: timeout = SessionManager.Timeout;
11: return SessionManager.StartSession(clientInfo);
12: }
13:
14: public void EndSession(Guid sessionID)
15: {
16: SessionManager.EndSession(sessionID);
17: }
18:
19: public IList<SessionInfo> GetActiveSessions()
20: {
21: return new List<SessionInfo>(SessionManager.CurrentSessionList.Values.ToArray<SessionInfo>());
22: }
23:
24: public void KillSessions(IList<Guid> sessionIDs)
25: {
26: SessionManager.KillSessions(sessionIDs);
27: }
28:
29: #endregion
30: }
31: }
32:基本上就是调用SessionManager对应的方法。
二、Service Hosting
在Artech.SessionManagement.Hosting.Program中的Main（）方法中，实际上是做了两件事情：
- 对SessionManagementService的Host。
- 通过Timer对象实现对Session列表的定期(5s)轮询。
1: namespace Artech.SessionManagement.Hosting
2: {
3: class Program
4: {
5: static void Main(string[] args)
6: {
7: using (ServiceHost host = new ServiceHost(typeof(SessionManagementService)))
8: {
9: host.Opened = delegate
10: {
11: Console.WriteLine("The session management service has been started up!");
12: };
13: host.Open();
14:
15: Timer timer = new Timer(
16: delegate { SessionManager.RenewSessions(); }, null, 0, 5000);
17:
18: Console.Read();
19: }
20: }
21: }
22: }
23:这是configuration,除了system.serviceModel相关配置外，还定义了配置了session timeout的时间，单位为”分”：
代码语言：javascript复制1: <?xml version="1.0" encoding="utf-8" ?>
2: <configuration>
3: <appSettings>
4: <add key="SessionTimeout" value="0.5"/>
5: </appSettings>
6: <system.serviceModel>
7: <services>
8: <service name="Artech.SessionManagement.Service.SessionManagementService">
9: <endpoint binding="netTcpBinding" bindingConfiguration="" contract="Artech.SessionManagement.Contract.ISessionManagement" />
10: <host>
11: <baseAddresses>
12: <add baseAddress="net.tcp://127.0.0.1:9999/sessionservice" />
13: </baseAddresses>
14: </host>
15: </service>
16: </services>
17: </system.serviceModel>
18: </configuration>
19:三、如何定义Client
这个service的实现已经完成，我们最后来介绍如何根据service的特点来定义我们的client程序了。我们的client是一个GUI应用（WinForm）。为了简便，我们把所有的逻辑定义在一个facade class上面：SessionUtility。
代码语言：javascript复制1: namespace Artech.SessionManagement.Client
2: {
3: public static class SessionUtility
4: {
5: static SessionUtility()
6: {
7: Callback = new SessionCallback();
8: Channel = new DuplexChannelFactory<ISessionManagement>(Callback, "sessionservice").CreateChannel();
9: }
10:
11: private static ISessionManagement Channel
12: { get; set; }
13:
14: private static ISessionCallback Callback
15: { get; set; }
16:
17: public static DateTime LastActivityTime
18: { get; set; }
19:
20: public static Guid SessionID
21: { get; set; }
22:
23: public static TimeSpan Timeout
24: { get; set; }
25:
26: public static void StartSession(SessionClientInfo clientInfo)
27: {
28: TimeSpan timeout;
29: SessionID = Channel.StartSession(clientInfo, out timeout);
30: Timeout = timeout;
31: }
32:
33: public static IList<SessionInfo> GetActiveSessions()
34: {
35: return Channel.GetActiveSessions();
36: }
37:
38: public static void KillSessions(IList<Guid> sessionIDs)
39: {
40: Channel.KillSessions(sessionIDs);
41: }
42: }
43: }
44:SessionUtility定义了连个public property：SessionID代表当前session的ID，Timeout代表Session timeout的时间，这两个属性都在StartSession中被初始化，而LastActivityTime代表的是最后一次用户交互的时间。上面的代码和简单，在这里就不多作介绍了。这里需要着重介绍我们的Callback class：
代码语言：javascript复制1: public class SessionCallback : ISessionCallback
2: {
3: #region ISessionCallback Members
4:
5: public TimeSpan Renew()
6: {
7: return SessionUtility.Timeout - (DateTime.Now - SessionUtility.LastActivityTime);
8: }
9:
10: public void OnSessionKilled(SessionInfo sessionInfo)
11: {
12: MessageBox.Show("The current session has been killed!", sessionInfo.SessionID.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Information);
13: Application.Exit();
14: }
15:
16: public void OnSessionTimeout(SessionInfo sessionInfo)
17: {
18: MessageBox.Show("The current session timeout!", sessionInfo.SessionID.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Information);
19: Application.Exit();
20: }
21:
22: #endregion
23: }
24:Renew()方法根据Timeout 和LastActivityTime计算出需要对该session延长的时间；OnSessionKilled和OnSessionTimeout在通过MessageBox显示相应的message后将程序退出。
我们简单简单一下本例子提供的client application。具有一个Form。我们把所有的功能集中在该Form中：开始一个新session、获得所有的活动的session列表、强行中止一个或多个Session。
这是StartSession按钮的click event handler：
代码语言：javascript复制1: private void buttonStartSession_Click(object sender, EventArgs e)
2: {
3: string hostName = Dns.GetHostName();
4: IPAddress[] ipAddressList = Dns.GetHostEntry(hostName).AddressList;
5: string ipAddress = string.Empty;
6: foreach (IPAddress address in ipAddressList)
7: {
8: if (address.AddressFamily == AddressFamily.InterNetwork)
9: {
10: ipAddress = address.ToString() ";";
11: }
12: }
13: ipAddress = ipAddress.TrimEnd(";".ToCharArray());
14:
15: string userName = this.textBoxUserName.Text.Trim();
16: if (string.IsNullOrEmpty(userName))
17: {
18: return;
19: }
20:
21: SessionClientInfo clientInfo = new SessionClientInfo() { IPAddress = ipAddress, HostName = hostName, UserName = userName };
22: SessionUtility.StartSession(clientInfo);
23: this.groupBox2.Enabled = false;
24: }获得当前PC的主机名称和IP地址，连同输入的user name创建SessionClientInfo 对象，调用SessionUtility的StartSession开始新的Session。
“Get All Active Session”，获取当前所有的活动的session，绑定到Datagrid：
代码语言：javascript复制1: private void buttonGet_Click(object sender, EventArgs e)
2: {
3: IList<SessionInfo> activeSessions = SessionUtility.GetActiveSessions();
4: this.dataGridViewSessionList.DataSource = activeSessions;
5: foreach (DataGridViewRow row in this.dataGridViewSessionList.Rows)
6: {
7: Guid sessionID = (Guid)row.Cells["SessionID"].Value;
8: row.Cells["IPAddress"].Value = activeSessions.Where(session=> session.SessionID == sessionID).ToList<SessionInfo>()[0].ClientInfo.IPAddress;
9: row.Cells["UserName"].Value = activeSessions.Where(session => session.SessionID == sessionID).ToList<SessionInfo>()[0].ClientInfo.UserName;
10: }
11: }“Kill Selected Session”按钮被点击，强行中止选中的Session：
代码语言：javascript复制1: private void buttonKill_Click(object sender, EventArgs e)
2: {
3: IList<Guid> sessionIDs = new List<Guid>();
4: foreach ( DataGridViewRow row in this.dataGridViewSessionList.Rows)
5: {
6: if ((string)row.Cells["Select"].Value == "1")
7: {
8: Guid sessionID = new Guid(row.Cells["SessionID"].Value.ToString());
9: if (sessionID == SessionUtility.SessionID)
10: {
11: MessageBox.Show("You cannot kill your current session!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
12: return;
13: }
14: sessionIDs.Add(sessionID);
15: }
16: }
17:
18: SessionUtility.KillSessions(sessionIDs);
19: }
20:由于不能中止自己当前的Session，所以当选中的列表中包含自己的SessionID，会显示一个messagebox提示不应该杀掉属于自己session。
到这里，实际上还有一件重要的事情没有解决，那就是如何动态修正SessionUtility.LastActivityTime。我们希望的事SessionUtility.LastActivityTime能够真正反映最后一次用户交互的时间。为此我们递归地注册每个control的MouseMove事件：
代码语言：javascript复制1: private void RegisterMouseMoveEvent(Control control)
2: {
3: control.MouseHover = delegate
4: {
5: SessionUtility.LastActivityTime = DateTime.Now;
6: };
7:
8: foreach (Control child in control.Controls)
9: {
10: this.RegisterMouseMoveEvent(child);
11: }
12: }
13:
14: private void FormSessionManagement_Load(object sender, EventArgs e)
15: {
16: this.dataGridViewSessionList.AutoGenerateColumns = false;
17: this.RegisterMouseMoveEvent(this);
18: }
19:如何你运行我们程序，输入user name开始session后，如果在30s内没有任何鼠标操作，下面的MessageBox将会弹出，当你点击OK按钮，程序会退出。
如何你同时开启多个client端程序，点击“Kill Selected Session”按钮，将会列出所有的Active session，就象我们在上面的截图所示的一样。你可以选择某个session，然后通过点击“Kill selected sessions”按钮强行中止它。通过另一个client application将马上得到反馈：弹出下面一个MessageBox。当你点击OK按钮，程序会退出
