Signals in Mercury

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In Java, we can handle signals using the sun.misc.Signal class. However, it’s important to note that this is a non-standard API and its use is generally discouraged. For more robust signal handling in Java applications, it’s recommended to use frameworks like Apache Commons Daemon or consider alternative approaches. Here’s an example of how signal handling could be implemented in Java:

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

public class SignalExample {
    public static void main(String[] args) {
        // Create a signal handler
        SignalHandler handler = new SignalHandler() {
            public void handle(Signal signal) {
                System.out.println();
                System.out.println(signal.getName());
                System.exit(0);
            }
        };

        // Register the signal handler for SIGINT and SIGTERM
        Signal.handle(new Signal("INT"), handler);
        Signal.handle(new Signal("TERM"), handler);

        System.out.println("awaiting signal");

        // Keep the program running
        try {
            Thread.sleep(Long.MAX_VALUE);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

This Java program demonstrates how to handle signals:

1. We import the necessary classes from the sun.misc package.

2. We create a SignalHandler that will be called when a signal is received. It prints the signal name and then exits the program.

3. We register this handler for both SIGINT (interrupt signal, usually triggered by Ctrl+C) and SIGTERM (termination signal).

4. The program then prints “awaiting signal” and enters an infinite sleep to keep it running until a signal is received.

To run this program:

$ javac SignalExample.java
$ java SignalExample
awaiting signal
^C
INT

When we run this program, it will block waiting for a signal. By typing ctrl-C (which the terminal shows as ^C), we can send a SIGINT signal, causing the program to print INT and then exit.

Note that this example uses non-standard APIs and may not work on all Java implementations. For production use, consider using more robust frameworks or alternative approaches for handling application lifecycle and shutdown.