Sample code that allows System.inheritedChannel() to work?

Question

Hi,
I would like to create a C program, which will launch a Java runtime. I want the C program to open a listening socket, then pass that listening socket to the started Java VM.
I should be able to do this, and have the java VM inherit the listening socket, and then in the Java program, I should be able to get the listening socket with System.inheritedChannel().
In theory, anyway, all the docs seem to state that this is possible. But the problem is that I haven't found any code that does this. I'm not sure how I should setup the listening socket so that its the one that is picked by the inheritedChannel() call. What happens if my C program has multiple sockets, both connected and listening? How is the correct one determined? And do I have to have any special implementation of SelectorProvider?
Finding a working sample would really help me figure this out. Or, just any program that already uses this mechanism somewhere.
Can someone point me to such a sample?
Thanks,
Greg

Answer 1

The following 'c' code will first create a LISTEN socket then pass it to the Java application following. This, with the previous post show both passing connected clients as-well-as service sockets to java via System.inheritedChannel().
#include "stdnet.h" // platform specific network headers
int
main(int argc,char *argv[])
     pid_t     childPid = (pid_t)-1;
     // setServiceOnHostPort() creates bound LISTEN socket
     int          service     = setServiceOnHostPort("127.0.0.1",13333);
     fprintf(stderr,"service socket is %d, on port %d\n",
          service,getServicePort(service));
     // create child process in which to start the jvm
     if               ((pid_t)0 > (childPid = fork()))
          fprintf(stderr,"Cannot fork(), errno = %d\n",errno);
          exit(-1);
     } else if     ((pid_t)0 != childPid) {
          // close replace the tty fd with our service (LISTEN) socket
          dup2(service,STDIN_FILENO);
          // close the others, just in case
          dup2(-1,STDOUT_FILENO);
          dup2(-1,STDERR_FILENO);
          // stdin == service so we can close service now
          close(service);
          execvp(argv[1],&argv[1]);
          /* Failed to start application, pause before exiting w/ 123 */
          _exit(123);
     } /* if          ((pid_t)0 > (childPid = fork())) */
     // parent can leave now, of course its better to see if jvm actially
     // started here by looking for child's exit code of 123.
     return(0);
} /* int main(int argc,char argv[]) /
Now the java code.
import java.io.File;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
public class jInetdApp
     public static void main(String[] args)
          throws Exception
          System.setOut(new PrintStream(new File(
               System.getProperty("user.dir") + "/java-inetd.out")));
          System.setErr(new PrintStream(new File(
               System.getProperty("user.dir") + "/java-inetd.err")));
          Object stdInObject = (Object)System.inheritedChannel();
          // started w/ connected socket
          if (stdInObject instanceof SocketChannel)
               SocketChannel channel =
                    (SocketChannel) stdInObject;
               Socket socket = channel.socket();
               System.err.println("channel: " + channel);
               System.err.println("socket: " + socket);
               PrintStream ps =
                    new PrintStream(socket.getOutputStream());
               ps.println("Hello world");
               ps.flush();
               ps.close();
               socket.shutdownInput();
               socket.shutdownOutput();
               socket.close();
          // started with service (LISTEN) socket
          } else if (stdInObject instanceof ServerSocketChannel) {
               ServerSocketChannel channel =
                    (ServerSocketChannel) stdInObject;
               ServerSocket socket =
                    (ServerSocket)channel.socket();
               System.err.println("channel: " + channel);
               System.err.println("socket: " + socket);
               Thread.sleep(30000);
               socket.close();
          // started from command line??
          } else {
               System.err.println("stdInObject: " + stdInObject);
          } if (stdInObject instanceof SocketChannel)
          System.err.flush();
          System.out.flush();
     } // public static void main(String[] args)
} // public class jInetdApp
I hope this is helps.
cj