有人可以解释以下代码吗？

import sun.misc.Unsafe;
import sun.nio.ch.DirectBuffer;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.reflect.Field;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class PingPongMapMain {
    public static void main(String... args) throws IOException {
        boolean odd;
        switch (args.length < 1 ? "usage" : args[0].toLowerCase()) {
            case "odd":
                odd = true;
                break;
            case "even":
                odd = false;
                break;
            default:
                System.err.println("Usage: java PingPongMain [odd|even]");
                return;        
        }
        int runs = 10000000;
        long start = 0;
        System.out.println("Waiting for the other odd/even");
        File counters = new File(System.getProperty("java.io.tmpdir"),"counters.deleteme");        
        counters.deleteOnExit();
        try (FileChannel fc = new RandomAccessFile(counters, "rw").getChannel()) {
        MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, 1024);
        long address = ((DirectBuffer) mbb).address();
        for (int i = -1; i < runs; i++) {
            for (; ; ) {
                long value = UNSAFE.getLongVolatile(null, address);
                boolean isOdd = (value & 1) != 0;
                if (isOdd != odd)
                    // wait for the other side.
                    continue;
                    // make the change atomic, just in case there is more than one odd/even process
                if (UNSAFE.compareAndSwapLong(null, address, value, value + 1))
                    break;
            }
            if (i == 0) {
                System.out.println("Started");
                start = System.nanoTime();
                }
            }
        }
        System.out.printf("... Finished, average ping/pong took %,d ns%n",
            (System.nanoTime() - start) / runs);
    }

   static final Unsafe UNSAFE;
   static {
        try {
            Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
            theUnsafe.setAccessible(true);
            UNSAFE = (Unsafe) theUnsafe.get(null);
        } catch (Exception e) {
        throw new AssertionError(e);
        }
    }
}

此示例显示“线程安全访问直接内存”，它用于在进程之间共享数据。在两个程序中运行时，一个带有奇数，另一个带有偶数。您会看到每个进程都通过持久共享内存来更改数据。

但是我对一些事情感到困惑：

1. tmp文件是用来做什么的？
   
2. UnSafe在这里做什么？
   
3. 为什么在这里不安全使用；
   
4. 为什么将字段强制转换为UnSafe类型，而不是sun.misc.Unsafe.getUnsafe（）？