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Java – Signal Handling

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In my earlier article, I talked about how to do a graceful shutdown your of Java application when Ctr-C, or the termination signal is intercepted. Now I am going to roughly show you how to do it using Java signal handling.

JVM signal handling is slightly different across different platforms, e.g. across Linux, HP-UX and Windows. So the signal handling program you write in Windows may not work in Linux or HP-UX. Unlike the previous article which is using shutdown hook, which is platform independent, if you want to use signal handling in Java, you have to know which signal(s) you want to handle.

E.g. for Unix/Linux based platform the signals are SEGV, ILL, FPE, BUS, SYS, CPU, FSZ, ABRT, INT, TERM, HUP, USR1, QUIT, BREAK, TRAP, PIPE.

For Windows based platform, the signals are SEGV, ILL, FPE, ABRT, INT, TERM, BREAK.

However, to really determine which signal can be handled in your target platform, you have to test it yourself.

Here is a simple program that you can use to test out signal handling in Java.

import sun.misc.Signal;
import sun.misc.SignalHandler;

public class SignalHandlerExample implements SignalHandler {

    private SignalHandler oldHandler;

    public static SignalHandler install(String signalName) {
        Signal diagSignal = new Signal(signalName);
        SignalHandlerExample instance = new SignalHandlerExample();
        instance.oldHandler = Signal.handle(diagSignal, instance);
        return instance;
    }

    public void handle(Signal signal) {
        System.out.println("Signal handler called for signal " 
              + signal);
        try {

            signalAction(signal);

            // Chain back to previous handler, if one exists
            if (oldHandler != SIG_DFL && oldHandler != SIG_IGN) {
                oldHandler.handle(signal);
            }

        } catch (Exception e) {
            System.out.println("handle|Signal handler 
                 failed, reason " + e.getMessage());
            e.printStackTrace();
        }
    }

    public void signalAction(Signal signal) {
        System.out.println("Handling " + signal.getName());
        System.out.println("Just sleep for 5 seconds.");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            System.out.println("Interrupted: " 
              + e.getMessage());
        }
    }

    public static void main(String[] args) {
        SignalHandlerExample.install("TERM");
        SignalHandlerExample.install("INT");
        SignalHandlerExample.install("ABRT");

        System.out.println("Signal handling example.");
        try {
            Thread.sleep(50000);
        } catch (InterruptedException e) {
            System.out.println("Interrupted: " + e.getMessage());
        }

    }
}

This program handles the TERM, INT, and ABRT signals. When it starts up, it will just sleep. During this time, if you press Ctr-C, the INT signal is triggered and signalAction is called.

Here is the sample output.

C:\>java -cp . SignalHandlerExample
Signal handling example.
Signal handler called for signal SIGINT
Handling INT
Just sleep for 5 seconds.


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RSS Feed for This Post8 Comment(s)

  1. joe | Feb 9, 2009 | Reply

    Hi,

    neat trick:) I used it in my database console tool, http://sf.net/projects/jdbcon

    Thanks!

  2. Arslan | Nov 26, 2009 | Reply

    Thank you for this article. It is quite cool. I simplified it for my particular use in handling a SIGPIPE.

    private void setupPipeSignalHandler()
    {
    Signal.handle(new Signal(“PIPE”), new SignalHandler()
    {
    public void handle(Signal signal)
    {
    System.exit(2);
    }
    });
    }

    Just a question regarding the static method install. Why not have this method as the constructor of the class. It just looks like it is doing the job of a conventional constructor.

  3. Karanth Srihari | Dec 10, 2009 | Reply

    Hi,

    This one exits after handling the signal.

    If i modify the try catch sleep in main like this

    try {
    for(int i=0;i <10;i++)
    {
    System.out.println(“Sleeping in Main for index i = ” + i);
    Thread.sleep(5000);
    }
    } catch (InterruptedException e) {
    System.out.println(“Interrupted: ” + e.getMessage());
    }

    and when i run this code, i get the following output:
    ——————————–
    Signal handling example.
    Sleeping in Main for index i = 0
    Sleeping in Main for index i = 1
    Sleeping in Main for index i = 2
    Sleeping in Main for index i = 3
    Sleeping in Main for index i = 4
    Sleeping in Main for index i = 5
    Sleeping in Main for index i = 6
    Signal handler called for signal SIGINT
    Handling INT
    Just sleep for 5 seconds in signalAction method.
    Sleeping in Main for index i = 7
    ——————————

    The program exists after 7!! it didnt continue till 10. What could be the reason? i gave “kill -INT pid”

    Thanks.

  4. anonymous | Mar 13, 2010 | Reply

    @Karanth: You didn’t tell your program to exit on SIGINT. You just printed some messages and slept 10s.
    If you overwrite the default handler for SIGINT you have to stop the program yourself (how is up to you then)

  5. anonymous | Mar 13, 2010 | Reply

    > slept 10s

    Sorry, this should have read “slept 5s”…

  6. Richard | Dec 14, 2010 | Reply

    Nice post!

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  8. sabbir | May 23, 2013 | Reply

    what is the library file required for sun.misc.* ?

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