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Java error: java.lang.IllegalArgumentException: signal already used by VM: INT

I am studying the Java problem (using IBM JVM 1.4.2 64-bit) on Red Hat Linux. I am wondering if anyone has seen this error message before and knows if there is a way around the problem?

Source:

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

public class SignalTest extends Thread
{
    private static Signal signal = new Signal("INT");

    private static ShutdownHandler handler = new ShutdownHandler();

    private static class ShutdownHandler implements SignalHandler
    {
        public void handle(Signal sig)
        {
        }
    }

    public static void main(String[] args)
    {
        try
        {
            Signal.handle(signal, handler);
        }
        catch(Throwable e)
        {
            e.printStackTrace();
        }

        try { Thread.sleep(5000); } catch(Exception e) { e.printStackTrace(); }

        System.exit(0);
    }
}

Output:

java.lang.IllegalArgumentException <Signal already used by VM: INT>
java.lang.IllegalArgumentException: Signal already used by VM: INT
at
com.ibm.misc.SignalDispatcher.registerSignal(SignalDispatcher.java:145)
at sun.misc.Signal.handle(Signal.java:199)
at xxx

Additional Information:

I found out something strange. The reason this fails is because I am running the program inside the shell script as a background process.

i.e. sigtest.sh:

#!/bin/bash
java -cp . SignalTest >> sigtest.log 2>&1 &

If I run the program from the command line or delete "&" (ie make it foreground inside the shell script), it has no problem ... I don’t understand why this is so.

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8 answers

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  • ibm.signalhandling.rs true/false

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-XX:-AllowUserSignalHandlers

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System.out.println("Hello");

handle :

z@zolty:/tmp/so$ java SignalTest & sleep 1s && kill -2 $!
[1] 20467
z@zolty:/tmp/so$ Hello
z@zolty:/tmp/so$
z@zolty:/tmp/so$ java SignalTest
[1]+  Done             java SignalTest
0

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0

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userx: *: 7260: 20:://userx:/USR//CSH

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0

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> grep Sig /proc/self/status
SigQ:   1/1030663
SigPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000001001006
SigCgt: 0000000000000000

Note that the bit for SIGINT (value 2) is set to SigIgn. When starting the IBM JVM with this mask, it refuses to install a handler for SIGINT. I worked on the problem by running the JVM through the Python shell, which resets the default SIGINT handler:

#!/usr/bin/env python

import os
import signal
import sys

signal.signal(signal.SIGINT, signal.SIG_DFL)

args = sys.argv[1:]
os.execv(args[0], args)

The first argument to the shell is the command java, then follow the arguments to the JVM.

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