Why doesn't start another process?

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November 3rd, 2012, 12:30 PM

marlonmin

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Why doesn't start another process?

I think this code should print the message more than once, but it only prints once. What's the problem? Thanks.

Code:

import java.io.IOException;

public class RestartApplication {

	public static void main(String[] args) {       
		System.out.println("Test restarting the application!");       
		restart();
	}

	private static void restart() {
		try{
			Runtime.getRuntime().exec("java RestartApplication");
		}catch(IOException ie){

		}
		System.exit(0);
	}   
}

November 4th, 2012, 01:02 AM

slink

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Hi marlonmin,

Your code may well be printing the message more than once, but the exec-ed call will be running in a different thread that will not have access to the console that outputs the first message; they will be totally separate processes.

Note though that it is not just going to print the message out twice, it is going to keep running and running, because each call spawns a new process. I am going to reboot my PC now to kill off the dozens of threads that are taking up 100% of my CPU

Hope this helps,
slink

Comments on this post

Lux Perpetua agrees: LOL! No, I would not advise running this code.

November 4th, 2012, 03:40 AM

Lux Perpetua

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Quote:

Originally Posted by marlonmin

I think this code should print the message more than once, but it only prints once. What's the problem? Thanks.

Your subprocess is piping its output back to the main process. It isn't printed automatically; you have to do it yourself. Here's an example. For obvious reasons, I didn't retain your infinite-respawn cycle. You may need to change the exec() command string to something appropriate for your system if you're not on Linux. (Anything that generates output without reading input will do.)

java Code:

Original - java Code

import java.io.IOException;
 
public class ProcessTest {
 
    public static void main(String[] args) {       
        System.out.println("Testing process creation...");       
        test_process();
    }
 
    private static void test_process() {
        Process p = null;
 
        try{
            /* Use a different command here if 'readlink' or
             * '/dev/stdout' don't exist on your system.  This code is
             * not meant to be portable.
             */
            p = Runtime.getRuntime().exec("readlink -f /dev/stdout");
        } catch (IOException ie) {
            System.err.println("Couldn't run process.");
            System.exit(1);
        }
 
        int num_bytes = 0;
        byte [] b = new byte[4096];
 
        try {
            num_bytes = p.getInputStream().read(b);
        } catch (IOException ie) {
            System.err.println("Couldn't read pipe.");
            System.exit(1);
        }
 
        System.out.write(b, 0, num_bytes);
    
        System.exit(0);
    }   
}

Why doesn't start another process?

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