Name: dbT83986 Date: 02/02/99


The method Socket.close() is usually not blocking (at least with default settings)

Let's consider a socket accepted from the local process (called the server)
and initiated from a remote process (called by client).

The problem is that under certain conditions in the server a call to Socket.close() blocks
until the socket is closed by the remote client. CTRL-C does not work either, the server
process has then to be killed by a kill -9.

Some of those conditions are met when:
* The call is made from a UI thread
* Another thread in the server process is blocked reading on the Socket input stream
* One thread in the client process is blocked reading on the Socket input stream
* The server process runs on Sun's Solaris JDK 1.1.5, 1.1.6 with native threads activated
(Solaris 2.5 and 2.6 version have the problem)

The following code provides an example of the problem.

Note: I think there is a related bug that I encountered for which I don't have time to
develop a test case to specifically identify it. Following is a high level of the problem:
It looks like with Solaris native threads (2.5, and 2.6), when some threads are busy
reading/writing on some Sockets with a remote process, then a call to System.exit(0) does
not trigger the exit of the Virtual Machine process as specified in the Java Language
Specifications.



/************************************************************
 This is the class to run on the "server"-side
This uses not-so clean inner classes to reduce # of files
to compile...
***********************************************************/

import java.net.*;
import java.io.*;
import java.awt.*;




public class TestSocketServer extends Thread {
private Socket thisSock_;
  
    public static void main(String argv[]) throws Exception {
TestSocketServer server = new TestSocketServer();
//Start threads that will set up the client/server connections and wait on sockets
server.start();

//Create a UI thread that will ask for socket closing
(server. new TestSocketServerPanel(server)).show();
      
    }

    //UI thread: a simple panel that trigger the closing of the Socket on the server side
    public class TestSocketServerPanel extends Frame {
public TestSocketServer server_;

public TestSocketServerPanel(TestSocketServer server) {
server_ = server;
}
       
public boolean mouseDown(Event e, int x, int y) {
System.out.println("Received UI request to close the socket ...");
server_.closeSocket();
return true;
}
    };

    //Spawn another thread itself reading on the socket the received.
    class WaitingThread extends Thread {
private Socket listenOn_;

public void run() {
try {
BufferedReader input = new BufferedReader(new InputStreamReader(listenOn_.getInputStream(), "8859_1"));
while(true) {
System.out.println("WaitingThread on server received:" + input.readLine());
}
} catch(Exception e) {
System.out.println("WaitingThread caught exception:"+e);
e.printStackTrace();
}
}

public void setSocket(Socket listenOn) {
listenOn_ = listenOn;
}
    };


    
    public void run() {

try {
//Create a Server socket to receive incoming calls
ServerSocket serverSock = new ServerSocket(1920, 30);

//Spawn a new process that will connect to us with a socket
System.out.println("Launching now the client process");
Process process = Runtime.getRuntime().exec(" /opt/java/jdk1.1.6/bin/appletviewer login.html");

//Wait until the other process has connected to us
System.out.println("Receiving incoming call...");
thisSock_ = serverSock.accept();
System.out.println("Received incoming call");


WaitingThread readingThread = new WaitingThread();
readingThread.setSocket(thisSock_);
readingThread.start();

} catch(Exception e) {
System.out.println("TestSocketServer caught exception:"+e);
e.printStackTrace();
}
    }


    public void closeSocket() {
try {
System.out.println("stop() method requested to close the socket");

System.out.println("Closing socket");
thisSock_.close();

/* When the bug described occurs this line is never reached unless the
client applet exits
*/

System.out.println("The socket was successfully closed");
      
System.exit(0);
} catch(Exception e) {
System.out.println("TestSocketServer caught exception:"+e);
e.printStackTrace();
}

    }
}






/*********************************************************
 This is the applet to run on the "client"-side
***********************************************************/

import java.net.*;
import java.io.*;
import java.applet.*;

public class TestSocketAppletClient extends Applet {
    public void start() {

try {
System.out.println("Client connecting to server ...");
Socket mySock = new Socket(InetAddress.getLocalHost(), 1920);


System.out.println("Client reading on socket ...");

// BufferedReader input = new BufferedReader(new InputStreamReader(mySock.getInputStream()));
//PrintWriter output = new PrintWriter(new OutputStreamWriter(mySock.getOutputStream()));
//Those 1.0 I/O code might well have nothing to do with the problem, just reproducing my own environment :-)
DataInputStream input = new DataInputStream(new BufferedInputStream(mySock.getInputStream()));
PrintStream output = new PrintStream(new BufferedOutputStream(mySock.getOutputStream()));

// while(true) {
byte buf[] = new byte[8];
"Hi server".getBytes(0, 8, buf, 0);
output.write(buf, 0 ,8);
output.flush();
System.out.println("client received:" + input.readLine());
output.flush();
// }
} catch(Exception e) {
System.out.println("TestSocketAppletClient caught exception:"+e);
e.printStackTrace();
}
    }

}



<HTML>
***************************************************************
This is the sample HTML page to invoque the applet
***************************************************************
<APPLET mayscript
CODE = "TestSocketAppletClient"
WIDTH = 420
HEIGHT = 145>
</APPLET>
(Review ID: 38415)
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