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LArray off-heap buffer library
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package xerial.larray.buffer;

import sun.misc.Unsafe;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.nio.ByteBuffer;

/**
 * Helper methods for using sun.misc.Unsafe.
 *
 * @author Taro L. Saito
 */
public class UnsafeUtil {

    public static Unsafe getUnsafe() {
        try {
            Field f = Unsafe.class.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            return Unsafe.class.cast(f.get(null));
        }
        catch(NoSuchFieldException e) {
            throw new IllegalStateException("sun.misc.Unsafe is not available in this JVM");
        }
        catch(IllegalAccessException e) {
            throw new IllegalStateException("sun.misc.Unsafe is not available in this JVM");
        }
    }

    public static Unsafe unsafe = getUnsafe();

    private static Constructor findDirectByteBufferConstructor() {
        try {
            return Class.forName("java.nio.DirectByteBuffer").getDeclaredConstructor(Long.TYPE, Integer.TYPE, Object.class);
        }
        catch(ClassNotFoundException e) {
            throw new IllegalStateException(String.format("Failed to find java.nio.DirectByteBuffer: $s", e.getMessage()));
        }
        catch(NoSuchMethodException e) {
            throw new IllegalStateException(String.format("Failed to find constructor f java.nio.DirectByteBuffer: $s", e.getMessage()));
        }
    }

    private static Constructor dbbCC = findDirectByteBufferConstructor();

    /**
     * Create a new DirectByteBuffer from a given address and size.
     * The returned DirectByteBuffer does not release the memory by itself.
     *
     * @param addr
     * @param size
     * @param att  object holding the underlying memory to attach to the buffer.
     *             This will prevent the garbage collection of the memory area that's
     *             associated with the new DirectByteBuffer
     * @return
     */
    public static ByteBuffer newDirectByteBuffer(long addr, int size, Object att) {
        dbbCC.setAccessible(true);
        Object b = null;
        try {
            b = dbbCC.newInstance(new Long(addr), new Integer(size), att);
            return ByteBuffer.class.cast(b);
        }
        catch(Exception e) {
            throw new IllegalStateException(String.format("Failed to create DirectByteBuffer: %s", e.getMessage()));
        }
    }


}