Running Runtime.getRuntime().exec() problem

[Alan Blass]

Hi!

I am running Runtime.getRuntime().exec() to run VLC (VideoLan) software within a servlet. The VLC software runs properly. I use it to record a multicast video streaming.

After running this command, the servlet returns to my AJAX call and my webpage loads.

Problem is: Any subsequent HTTP get or post, the server (Apache Tomcat 7) does not respond.

It is only about after 2 minutes, the server responds back to my browser.

Anyone has the same problem with VLC?

Anyone has any suggestions to advice me to investigate further?

All comments welcomed.

Thanks.

[James Sabre]

There are several traps that one can fall into using Runtime.exec() so you should read the 4 sections of http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html and implement all the recommendations. If this fails to solve the problem then posting the code might help.

[Bear Bibeault]

But I wonder what use running a GUI client like VLC is from a servlet? When the user is remote, the GUI will appear on the server machine. Is that the intention?

[Alan Blass]

Hi! Thanks for your replies.

When the remote user wants to start recording, I start VLC on the server and start recording the multicast video. Here is my code:

public class RecordingServlet extends HttpServlet {
   
    private TelnetClient telnet = new TelnetClient();
    private InputStream in;
    private PrintStream ps;
    private char prompt = '>';

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
                    Runtime.getRuntime().exec("vlc.exe --intf telnet --rtsp-caching=5000");                         
                    telnet.connect("localhost", 4212);

                    if (telnet.isConnected()) {
                        
                        in = telnet.getInputStream();
                        ps = new PrintStream(telnet.getOutputStream());

						readUntil("Password: ");
						write("admin");
						readUntil("Welcome, Master");
						readUntil(prompt + "");
                        write("new s1 broadcast enabled");
						readUntil(prompt + "");
						write("setup s1 input rtsp://192.168.1.182/axis-media/media.amp?videocodec=h264&streamprofile=Quality&audio=1");
						readUntil(prompt + "");
						write("setup s1 output #duplicate{dst=std{access=file,mux=mp4,dst='test.mp4'}}");
						readUntil(prompt + "");
						write("control s" + cameraId + " play");
						readUntil(prompt + "");
                        write("quit");

						
						result = "true";
						out.print(result);                       

                    } else {                        
                        out.println("Problem with telnet connection");
                    }
                    telnet.disconnect();
        }
}

What could be holding up VLC or tomcat that it stopped responding for 2 minutes?

Many thanks.

[William Brogden]

Perhaps VLC is writing to the std err stream, which you are not consuming. A full buffer would cause VLC to hang.

Also - you are doing this all in the request processing Thread - not a good idea. I would certainly execute all that code in a separate Runnable object using its own Thread.

Bill

[James Sabre]

Alan Blass wrote:
What could be holding up VLC or tomcat that it stopped responding for 2 minutes?

You have the potential for deadlock on both the process stdout and stderr. You really do need to read the 4 sections of the traps article and to implement all the recommendations.. Added to this, your servlet is not thread safe since you have state stored as instance variables.

Both these are critical flaws.