Advanced .NET Remoting: 第 9 章 3.在 Remoting 中传递额外的运行时信息
Advanced .NET Remoting：第 9 章
3.传递运行时信息
前面使用的接收器 ( Sink ) 是 IClientChannelSinks 与 IServerChannelSinks。这意味着它们工作在格式化器已经序列化 IMessage 对象 之后 。而对于 IMessageSink 来说，不同的是，可以直接工作在消息的内容被格式化 之前 。这意味着，你对 IMessage 内容的任何修改都将被序列化，进而反映到最终的流中。
注意：即使你试图在 IClienntChannelSink 中修改 IMessage 对象的内容，需要注意的是，这些修改 不会 被传播到服务器端，因为序列化的流已经通过 IMessage 对象生成了。
基于该区别，客户端 IMessageSink 可以用来从客户端将运行时信息传递到服务器端。在随后的示例中，我将向您展示如何将客户端的线程 ( thread ) 的当前优先级别 ( priority ) 传递到服务器端，以便远程方法可以运行在同样的优先级上。
为了从客户端向服务器端发送任意数据，你需要将它加入到 Message 对象的逻辑调用上下文 ( logical call context ) 中。通过这种方式，你可以传递可序列化对象 ( serializable ) 或者扩展了 MarshalByRefObject 的对象。例如，为了在对服务器上任何方法的调用中，传递客户端的线程的当前上下文，你可以实现如下的 SyncProcessMessage() 方法：
public IMessage SyncProcessMessage(IMessage msg)
{
if (msg as IMethodCallMessage != null)
{
LogicalCallContext lcc =
(LogicalCallContext) msg.Properties["__CallContext"];
lcc.SetData("priority",Thread.CurrentThread.Priority);
return _nextMsgSink.SyncProcessMessage(msg);
}
else
{
return _nextMsgSink.SyncProcessMessage(msg);
}
}
对于 AsyncProcessMessage() 方法也同样处理。
public IMessageCtrl AsyncProcessMessage(IMessage msg, IMessageSink replySink)
{
if (msg as IMethodCallMessage != null)
{
LogicalCallContext lcc =
(LogicalCallContext) msg.Properties["__CallContext"];
lcc.SetData("priority",Thread.CurrentThread.Priority);
return _nextMsgSink.AsyncProcessMessage(msg,replySink);
}
else
{
return _nextMsgSink.AsyncProcessMessage(msg,replySink);
}
}
在服务器端，你也必须实现一个 IServerChannelSink 来从 IMessage 对象中提取调用上下文信息 ( call context )，然后设置到 Thread.CurrentThread.Priority 上来应用该值。
public ServerProcessing ProcessMessage(IServerChannelSinkStack sinkStack,
IMessage requestMsg,
ITransportHeaders requestHeaders,
Stream requestStream,
out IMessage responseMsg,
out ITransportHeaders responseHeaders,
out Stream responseStream)
{
LogicalCallContext lcc =
(LogicalCallContext) requestMsg.Properties["__CallContext"];
// storing the current priority
ThreadPriority oldprio = Thread.CurrentThread.Priority;
// check if the logical call context contains "priority"
if (lcc != null && lcc.GetData("priority") != null)
{
// fetch the priority from the call context
ThreadPriority priority =
(ThreadPriority) lcc.GetData("priority");
Console.WriteLine(" -> Pre-execution priority change {0} to {1}",
oldprio.ToString(),priority.ToString());
// set the priority
Thread.CurrentThread.Priority = priority;
}
// push on the stack and pass the call to the next sink
// the old priority will be used as "state" for the response
sinkStack.Push(this,oldprio);
ServerProcessing spres = _next.ProcessMessage (sinkStack,
requestMsg, requestHeaders, requestStream,
out responseMsg,out responseHeaders,out responseStream);
// restore priority if call is not asynchronous
if (spres != ServerProcessing.Async)
{
if (lcc != null && lcc.GetData("priority") != null)
{
Console.WriteLine(" -> Post-execution change back to {0}",oldprio);
Thread.CurrentThread.Priority = oldprio;
}
}
return spres;
}
用于服务器端的接收器的接收器提供器非常简单。它看起来多少与前面的 IServerChannelSink 是相同的。
在客户端，这种方式有一点不太方便。请记住，你现在是在实现 IMessageSink 而不是 IClientChannelSing。如果寻找 IMessageSinkProvider 的话不会有 任何结果，所以，此时你还是不得不实现一个 IClientChannelSink - 即使实际上该连接器是 IMessageSink。当查看随后部分的 IClientChannelSinkProvider 接口的时候，就会发现这个问题。
IClientChannelSink CreateSink(IChannelSender channel,
string url,
object remoteChannelData);
这个接口说明，在任何场景下，CreateSink() 都只会返回 IClientChannelSink，即使你的连接器只需要实现 IMessageSink。所以现在你不得不扩展你的 IMessageSink 同时去实现 IClientChannelSink。你还不得不使用条件判断，因为 IClientChannelSink 也定义来更多的方法需要实现。这些方法将在这个连接器作为通道连接器 ( channel sink ) 的时候而不是作为消息连接器 ( 也就是说，在格式化器之后 ) 被调用。 你可能不希望你的用户将该连接器放置在格式化器 之后 ( 它在这里并不有效，因为它修改了 IMessage 对象的内容 )，所以你会希望对于这些方法抛出异常。
完整的客户端 PriorityEmitterSink 代码，会在用于错误的顺序时抛出这些异常，如列表 13-12 所示：
using System;
using System.Collections;
using System.IO;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Messaging;
using System.Threading;
namespace PrioritySinks
{
public class PriorityEmitterSink : BaseChannelObjectWithProperties,
IClientChannelSink, IMessageSink
{
private IMessageSink _nextMsgSink;
public IMessageCtrl AsyncProcessMessage(IMessage msg, IMessageSink replySink)
{
// only for method calls
if (msg as IMethodCallMessage != null)
{
LogicalCallContext lcc =
(LogicalCallContext) msg.Properties["__CallContext"];
lcc.SetData("priority",Thread.CurrentThread.Priority);
return _nextMsgSink.AsyncProcessMessage(msg,replySink);
}
else
{
return _nextMsgSink.AsyncProcessMessage(msg,replySink);
}
}
public IMessage SyncProcessMessage(IMessage msg)
{
// only for method calls
if (msg as IMethodCallMessage != null)
{
LogicalCallContext lcc =
(LogicalCallContext) msg.Properties["__CallContext"];
lcc.SetData("priority",Thread.CurrentThread.Priority);
return _nextMsgSink.SyncProcessMessage(msg);
}
else
{
return _nextMsgSink.SyncProcessMessage(msg);
}
}
public PriorityEmitterSink (object next)
{
if (next as IMessageSink != null)
{
_nextMsgSink = (IMessageSink) next;
}
}
public IMessageSink NextSink
{
get
{
return _nextMsgSink;
}
}
public IClientChannelSink NextChannelSink
{
get
{
throw new RemotingException("Wrong sequence.");
}
}
public void AsyncProcessRequest(IClientChannelSinkStack sinkStack,
IMessage msg,
ITransportHeaders headers,
Stream stream)
{
throw new RemotingException("Wrong sequence.");
}
public void AsyncProcessRequest(IClientChannelSinkStack sinkStack,
IMessage msg,
ITransportHeaders headers,
Stream stream)
{
throw new RemotingException("Wrong sequence.");
}
public void AsyncProcessResponse(
IClientResponseChannelSinkStack sinkStack,
object state,
ITransportHeaders headers,
Stream stream)
{
throw new RemotingException("Wrong sequence.");
}
public System.IO.Stream GetRequestStream(IMessage msg,
ITransportHeaders headers)
{
throw new RemotingException("Wrong sequence.");
}
public void ProcessMessage(IMessage msg,
ITransportHeaders requestHeaders,
Stream requestStream,
out ITransportHeaders responseHeaders,
out Stream responseStream)
{
throw new RemotingException("Wrong sequence.");
}
}
}
客户端的 PriorityEmitterSinkProvider 如列表 13-13 所示，实现很直接。只有方法 CreateSink() 比较值得关注。
列表 13-13 客户端的 PriorityEmitterSinkProvider
using System;
using System.Collections;
using System.Runtime.Remoting.Channels;
namespace PrioritySinks
{
public class PriorityEmitterSinkProvider: IClientChannelSinkProvider
{
private IClientChannelSinkProvider next = null;
public PriorityEmitterSinkProvider(IDictionary properties,
ICollection providerData)
{
// not needed
}
public IClientChannelSink CreateSink(IChannelSender channel,
string url, object remoteChannelData)
{
IClientChannelSink nextsink =
next.CreateSink(channel,url,remoteChannelData);
return new PriorityEmitterSink(nextsink);
}
public IClientChannelSinkProvider Next
{
get { return next; }
set { next = value; }
}
}
}
列表 13-14 是服务器端的 IServerChannelSink 实现，与客户端不同，它不是 IMessageSink，所以该实现更为一致。你不需要在这里实现任何其它接口。
列表 13-14 服务器端的 PriorityChangerSink
using System;
using System.Collections;
using System.IO;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Messaging ;
using System.Runtime.Remoting.Channels;
using System.Threading;
namespace PrioritySinks
{
public class PriorityChangerSink : BaseChannelObjectWithProperties,
IServerChannelSink, IChannelSinkBase
{
private IServerChannelSink _next;
public PriorityChangerSink (IServerChannelSink next)
{
_next = next;
}
public void AsyncProcessResponse (
IServerResponseChannelSinkStack sinkStack,
Object state,
IMessage msg,
ITransportHeaders headers,
Stream stream)
{
// restore the priority
ThreadPriority priority = (ThreadPriority) state;
Console.WriteLine(" -> Post-execution change back to {0}",priority);
Thread.CurrentThread.Priority = priority;
}
public Stream GetResponseStream (IServerResponseChannelSinkStack sinkStack,
Object state,
IMessage msg,
ITransportHeaders headers )
{
return null;
}
public ServerProcessing ProcessMessage(IServerChannelSinkStack sinkStack,
IMessage requestMsg,
ITransportHeaders requestHeaders,
Stream requestStream,
out IMessage responseMsg,
out ITransportHeaders responseHeaders,
out Stream responseStream)
{
LogicalCallContext lcc =
(LogicalCallContext) requestMsg.Properties["__CallContext"];
// storing the current priority
ThreadPriority oldprio = Thread.CurrentThread.Priority;
// check if the logical call context contains "priority"
if (lcc != null && lcc.GetData("priority") != null)
{
// fetch the priority from the call context
ThreadPriority priority =
(ThreadPriority) lcc.GetData("priority");
Console.WriteLine("-> Pre-execution priority change {0} to {1}",
oldprio.ToString(),priority.ToString());
// set the priority
Thread.CurrentThread.Priority = priority;
}
// push on the stack and pass the call to the next sink
// the old priority will be used as "state" for the response
sinkStack.Push(this,oldprio);
ServerProcessing spres = _next.ProcessMessage (sinkStack,
requestMsg, requestHeaders, requestStream,
out responseMsg,out responseHeaders,out responseStream);
// restore priority if call is not asynchronous
if (spres != ServerProcessing.Async)
{
if (lcc != null && lcc.GetData("priority") != null)
{
Console.WriteLine("-> Post-execution change back to {0}",oldprio);
Thread.CurrentThread.Priority = oldprio;
}
}
return spres;
}
public IServerChannelSink NextChannelSink
{
get {return _next;}
set {_next = value;}
}
}
}
列表 13-15 是相关的服务器端连接器提供器，它实现了接口 IServerChannelSinkProvider。
列表 13-15 服务器端的 PriorityChangerSinkProvider
using System;
using System.Collections;
using System.Runtime.Remoting.Channels;
namespace PrioritySinks
{
public class PriorityChangerSinkProvider: IServerChannelSinkProvider
{
private IServerChannelSinkProvider next = null;
public PriorityChangerSinkProvider(IDictionary properties,
ICollection providerData)
{
// not needed
}
public void GetChannelData (IChannelDataStore channelData)
{
// not needed
}
public IServerChannelSink CreateSink (IChannelReceiver channel)
{
IServerChannelSink nextSink = next.CreateSink(channel);
return new PriorityChangerSink(nextSink);
}
public IServerChannelSinkProvider Next
{
get { return next; }
set { next = value; }
}
}
}
为了测试该连接器的组合，使用如下的 SAO (服务器端激活对象) ，它会返回服务器端的当前线程的优先级：
public class TestSAO: MarshalByRefObject
{
public String getPriority()
{
return System.Threading.Thread.CurrentThread.Priority.ToString();
}
}
这个 SAO 将被客户端使用不同的线程优先级调用多次。服务器端使用的配置文件如下所示：
<configuration>
<system.runtime.remoting>
<application>
<channels>
<channel ref="http" port="5555">
<serverProviders>
<formatter ref="soap" />
<provider
type="PrioritySinks.PriorityChangerSinkProvider, PrioritySinks" />
</serverProviders>
</channel>
</channels>
<service>
<wellknown mode="Singleton"
type="Server.TestSAO, Server" objectUri="TestSAO.soap" />
</service>
</application>
</system.runtime.remoting>
</configuration>
客户端的配置文件如下所示：
<configuration>
<system.runtime.remoting>
<application>
<channels>
<channel ref="http">
<clientProviders>
<provider
type="PrioritySinks.PriorityEmitterSinkProvider, PrioritySinks" />
<formatter ref="soap" />
</clientProviders>
</channel>
</channels>
<client>
<wellknown type="Server.TestSAO, generated_meta"
url="http://localhost:5555/TestSAO.soap" />
</client>
</application>
</system.runtime.remoting>
</configuration>
在用于测试的客户端，你可以使用 SoapSuds 来抽取元数据。当你运行如列表 13-16 所示的应用程序的时候，将会看到如图 13-8 所示的输出。
using System;
using System.Runtime.Remoting;
using Server; // from generated_meta.dll
using System.Threading;
namespace Client
{
delegate String getPrioAsync();
class Client
{
static void Main(string[] args)
{
String filename = "client.exe.config";
RemotingConfiguration.Configure(filename);
TestSAO obj = new TestSAO();
test(obj);
Thread.CurrentThread.Priority = ThreadPriority.Highest;
test(obj);
Thread.CurrentThread.Priority = ThreadPriority.Lowest;
test(obj);
Thread.CurrentThread.Priority = ThreadPriority.Normal;
test(obj);
Console.ReadLine();
}
static void test(TestSAO obj)
{
Console.WriteLine("----------------- START TEST CASE ---------------");
Console.WriteLine(" Local Priority: {0}",
Thread.CurrentThread.Priority.ToString());
String priority1 = obj.getPriority();
Console.WriteLine(" Remote priority: {0}",priority1.ToString());
Console.WriteLine("----------------- END TEST CASE ---------------");
}
}
}
图 13-8 通过客户端测试的输出，展示了连接器如愿工作
