Skip to content

Instantly share code, notes, and snippets.

@mbelop

mbelop/SimpleTest.java Secret

Last active May 25, 2018
Embed
What would you like to do?
import sun.misc.Unsafe;
import java.nio.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
public class SimpleTest3
{
public static final Unsafe UNSAFE;
public static final long BYTE_BUFFER_ADDRESS_FIELD_OFFSET;
static {
Unsafe unsafe = null;
try {
Constructor<Unsafe> unsafeConstructor = Unsafe.class.getDeclaredConstructor();
unsafeConstructor.setAccessible(true);
unsafe = unsafeConstructor.newInstance();
Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
theUnsafe.setAccessible(true);
unsafe = (Unsafe) theUnsafe.get(null);
BYTE_BUFFER_ADDRESS_FIELD_OFFSET = unsafe.objectFieldOffset(Buffer.class.getDeclaredField("address"));
} catch (final Exception ex) {
throw new RuntimeException(ex);
}
UNSAFE = unsafe;
}
public static long address(final ByteBuffer buffer)
{
if (!buffer.isDirect())
throw new IllegalArgumentException("buffer.isDirect() must be true");
return UNSAFE.getLong(buffer, BYTE_BUFFER_ADDRESS_FIELD_OFFSET);
}
public static void main(String[] args)
{
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(128);
assert byteBuffer.isDirect() == true;
long addressOffset = address(byteBuffer);
System.out.println("addressOffset=" + addressOffset);
UNSAFE.putInt(null, addressOffset + 0, 42);
if (UNSAFE.getInt(null, addressOffset + 0) == 42)
System.out.println("The magic of unsafe.");
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment