A fun demo of unexpected (to me) file timestamp behaviour on Linux

Stamper.java

import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.time.Instant;

/**
 * Run this program, then kill -9 it. Then stat and cat the file it writes to, and compare the file's modification
 * timestamp to the timestamp written to the file.
 * <p>
 * Note that this code never flushes the file, but because it is memory-mapped, the kernel will flush it after the
 * process dies.
 */
public class Stamper {

    public static void main(String[] args) throws IOException {
        Path path = Files.createTempFile(Paths.get(System.getProperty("user.home")), Stamper.class.getSimpleName(), ".txt");
        System.out.println(path);
        FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE);
        int timestampLength = Instant.now().toString().length();
        MappedByteBuffer buffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, timestampLength + 1);
        buffer.put(timestampLength, (byte) '\n');
        while (true) {
            buffer.clear();
            buffer.put(Instant.now().toString().getBytes());
        }
    }

}