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Library for efficiently working with heap and off-heap memory
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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.airlift.slice;

import sun.misc.Unsafe;

import java.lang.reflect.Field;
import java.nio.Buffer;
import java.nio.ByteOrder;

import static io.airlift.slice.Preconditions.checkArgument;
import static sun.misc.Unsafe.ARRAY_BOOLEAN_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_BYTE_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_DOUBLE_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_FLOAT_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_INT_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_LONG_INDEX_SCALE;
import static sun.misc.Unsafe.ARRAY_SHORT_INDEX_SCALE;

final class JvmUtils
{
    static final Unsafe unsafe;
    private static final long ADDRESS_OFFSET;

    static {
        if (!ByteOrder.LITTLE_ENDIAN.equals(ByteOrder.nativeOrder())) {
            throw new UnsupportedOperationException("Slice only supports little endian machines.");
        }

        try {
            // fetch theUnsafe object
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            unsafe = (Unsafe) field.get(null);
            if (unsafe == null) {
                throw new RuntimeException("Unsafe access not available");
            }

            // verify the stride of arrays matches the width of primitives
            assertArrayIndexScale("Boolean", ARRAY_BOOLEAN_INDEX_SCALE, 1);
            assertArrayIndexScale("Byte", ARRAY_BYTE_INDEX_SCALE, 1);
            assertArrayIndexScale("Short", ARRAY_SHORT_INDEX_SCALE, 2);
            assertArrayIndexScale("Int", ARRAY_INT_INDEX_SCALE, 4);
            assertArrayIndexScale("Long", ARRAY_LONG_INDEX_SCALE, 8);
            assertArrayIndexScale("Float", ARRAY_FLOAT_INDEX_SCALE, 4);
            assertArrayIndexScale("Double", ARRAY_DOUBLE_INDEX_SCALE, 8);

            // fetch the address field for direct buffers
            ADDRESS_OFFSET = unsafe.objectFieldOffset(Buffer.class.getDeclaredField("address"));
        }
        catch (ReflectiveOperationException e) {
            throw new RuntimeException(e);
        }
    }

    private static void assertArrayIndexScale(String name, int actualIndexScale, int expectedIndexScale)
    {
        if (actualIndexScale != expectedIndexScale) {
            throw new IllegalStateException(name + " array index scale must be " + expectedIndexScale + ", but is " + actualIndexScale);
        }
    }

    static long bufferAddress(Buffer buffer)
    {
        checkArgument(buffer.isDirect(), "buffer is not direct");

        return unsafe.getLong(buffer, ADDRESS_OFFSET);
    }

    private JvmUtils() {}
}