Why does this simple use of JNA cause a fork() on Mac OS X?

Question

Here's a simple use of the JNA library for creating hard links in Java:

import com.sun.jna.Library;
import com.sun.jna.Native;
import java.io.File;
import java.io.IOException;

public final class HardLink {

    private static final LibC LIBC = (LibC)Native.loadLibrary("c", LibC.class);

    private HardLink() {
    }

    public static void link(File src, File dest) throws IOException {
        if (LIBC.link(src.toString(), dest.toString()) != 0)
            throw new IOException(LIBC.strerror(Native.getLastError()));
    }

    public static void main(String[] args) throws Exception {
        System.out.println("Attempting to hardlink " + args[0] + " -> " + args[1]);
        HardLink.link(new File(args[0]), new File(args[1]));
    }

    private interface LibC extends Library {
        int link(String from, String to);
        String strerror(int errno);
    }
}

When this program is run on Mac OS X 10.7.4 (Lion) using JNA 3.4.0, it does work, but for some reason it is doing a fork() - and I say that because it causes the Java icon to bouncy pop-up (appear) in the task bar with "HardLink" in the command bar as the program name.

My question is: why is JNA doing a fork() (or is it)? Is there something wrong with this program?

Note: I'm not interested in other ways to hard link files from Java. This is just an example.

Answer 1

JNA loads some AWT classes unless you're running headless. It's the loading of AWT-related classes (including Swing) which cause the java process to appear in the OSX Dock.

Run your program with -Djava.awt.headless=true. This will prevent it from showing up in the OSX dock.