我在一个多线程TCP服务器中使用互锁的Monitor.Wait和Monitor.Pulse时遇到了问题。为了说明我的问题,这是我的服务器代码:
public class Server
{
TcpListener listener;
Object sync;
IHandler handler;
bool running;
public Server(IHandler handler, int port)
{
this.handler = handler;
IPAddress address = Dns.GetHostEntry(Dns.GetHostName()).AddressList[0];
listener = new TcpListener(address, port);
sync = new Object();
running = false;
}
public void Start()
{
Thread thread = new Thread(ThreadStart);
thread.Start();
}
public void Stop()
{
lock (sync)
{
listener.Stop();
running = false;
Monitor.Pulse(sync);
}
}
void ThreadStart()
{
if (!running)
{
listener.Start();
running = true;
lock (sync)
{
while (running)
{
try
{
listener.BeginAcceptTcpClient(new AsyncCallback(Accept), listener);
Monitor.Wait(sync); // Release lock and wait for a pulse
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
}
}
}
}
void Accept(IAsyncResult result)
{
// Let the server continue listening
lock (sync)
{
Monitor.Pulse(sync);
}
if (running)
{
TcpListener listener = (TcpListener)result.AsyncState;
using (TcpClient client = listener.EndAcceptTcpClient(result))
{
handler.Handle(client.GetStream());
}
}
}
}
以下是我的客户端代码:
class Client
{
class EchoHandler : IHandler
{
public void Handle(Stream stream)
{
System.Console.Out.Write("Echo Handler: ");
StringBuilder sb = new StringBuilder();
byte[] buffer = new byte[1024];
int count = 0;
while ((count = stream.Read(buffer, 0, 1024)) > 0)
{
sb.Append(Encoding.ASCII.GetString(buffer, 0, count));
}
System.Console.Out.WriteLine(sb.ToString());
System.Console.Out.Flush();
}
}
static IPAddress localhost = Dns.GetHostEntry(Dns.GetHostName()).AddressList[0];
public static int Main()
{
Server server1 = new Server(new EchoHandler(), 1000);
Server server2 = new Server(new EchoHandler(), 1001);
server1.Start();
server2.Start();
Console.WriteLine("Press return to test...");
Console.ReadLine();
// Note interleaved ports
SendMsg("Test1", 1000);
SendMsg("Test2", 1001);
SendMsg("Test3", 1000);
SendMsg("Test4", 1001);
SendMsg("Test5", 1000);
SendMsg("Test6", 1001);
SendMsg("Test7", 1000);
Console.WriteLine("Press return to terminate...");
Console.ReadLine();
server1.Stop();
server2.Stop();
return 0;
}
public static void SendMsg(String msg, int port)
{
IPEndPoint endPoint = new IPEndPoint(localhost, port);
byte[] buffer = Encoding.ASCII.GetBytes(msg);
using (Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
s.Connect(endPoint);
s.Send(buffer);
}
}
}
客户端发送了七条消息,但服务器只打印了四条:
按回车键进行测试...我怀疑监视器在允许服务器的
按回车键终止... Echo Handler: Test1 Echo Handler: Test3 Echo Handler: Test2 Echo Handler: Test4
Accept
方法中发生 Pulse
之前就已经发生了 Wait
(在 ThreadStart
方法中),即使 ThreadStart
方法仍然持有对 sync
对象的锁,直到它调用 Monitor.Wait()
,然后 Accept
方法可以获取该锁并发送其 Pulse
。如果您在服务器的 Stop()
方法中注释掉这两行代码,则可以解决此问题://listener.Stop();
//running = false;
当服务器的
Stop()
方法被调用时,剩余的消息将出现(即唤醒服务器的sync
对象会使其分派剩余的传入消息)。在我看来,这只能发生在ThreadStart
和Accept
方法之间的竞态条件中,但是围绕sync
对象的锁应该可以防止这种情况发生。有什么想法吗?
非常感谢, 西蒙。
附注:请注意,我意识到输出显示顺序等问题,我特别询问锁和监视器之间的竞争条件。谢谢,SH。