我在多线程 TCP 服务器中遇到了联锁 Monitor.Wait 和 Monitor.Pulse 的问题。为了演示我的问题,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());
}
}
}
}
这是我的客户代码:
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 7 条消息,但服务器只打印 4 条:
按回车测试... 按回车键终止... 回声处理程序:Test1 回声处理程序:Test3 回声处理器:Test2 回声处理程序:Test4
我怀疑监视器通过允许在发生(在方法中)之前发生Pulse
(在服务器的方法中)而感到困惑,即使在它调用之前应该仍然拥有对象上的锁,然后该方法可以获得锁并发送它的. 如果您在服务器的方法中注释掉这两行:Accept
Wait
ThreadStart
ThreadStart
sync
Monitor.Wait()
Accept
Pulse
Stop()
//listener.Stop();
//running = false;
调用服务器的方法时会出现剩余的消息Stop()
(即唤醒服务器的sync
对象会导致它分派剩余的传入消息)。在我看来,这只能发生在ThreadStart
andAccept
方法之间的竞争条件下,但是对象周围的锁sync
应该可以防止这种情况发生。
有任何想法吗?
非常感谢,西蒙。
附言。请注意,我知道输出出现乱序等,我特别询问锁和监视器之间的竞争条件。干杯,SH。