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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.kafka.common.utils;

import java.io.IOException;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;

import static java.lang.invoke.MethodHandles.constant;
import static java.lang.invoke.MethodHandles.dropArguments;
import static java.lang.invoke.MethodHandles.filterReturnValue;
import static java.lang.invoke.MethodHandles.guardWithTest;
import static java.lang.invoke.MethodHandles.lookup;
import static java.lang.invoke.MethodType.methodType;

/**
 * Utility methods for MappedByteBuffer implementations. The unmap implementation was inspired by the one in Lucene's MMapDirectory.
 */
public final class MappedByteBuffers {

	// null if unmap is not supported
	private static final MethodHandle UNMAP;

	// null if unmap is supported
	private static final RuntimeException UNMAP_NOT_SUPPORTED_EXCEPTION;

	static {
		Object unmap = null;
		RuntimeException exception = null;
		try {
			unmap = lookupUnmapMethodHandle();
		} catch (RuntimeException e) {
			exception = e;
		}
		if (unmap != null) {
			UNMAP = (MethodHandle) unmap;
			UNMAP_NOT_SUPPORTED_EXCEPTION = null;
		} else {
			UNMAP = null;
			UNMAP_NOT_SUPPORTED_EXCEPTION = exception;
		}
	}

	private MappedByteBuffers() {
	}

	public static void unmap(String resourceDescription, MappedByteBuffer buffer) throws IOException {
		if (!buffer.isDirect())
			throw new IllegalArgumentException("Unmapping only works with direct buffers");
		if (UNMAP == null)
			throw UNMAP_NOT_SUPPORTED_EXCEPTION;

		try {
			UNMAP.invokeExact((ByteBuffer) buffer);
		} catch (Throwable throwable) {
			throw new IOException("Unable to unmap the mapped buffer: " + resourceDescription, throwable);
		}
	}

	private static MethodHandle lookupUnmapMethodHandle() {
		final MethodHandles.Lookup lookup = lookup();
		try {
			if (Java.IS_JAVA9_COMPATIBLE)
				return unmapJava9(lookup);
			else
				return unmapJava7Or8(lookup);
		} catch (ReflectiveOperationException | RuntimeException e1) {
			throw new UnsupportedOperationException("Unmapping is not supported on this platform, because internal " + "Java APIs are not compatible with this Kafka version", e1);
		}
	}

	private static MethodHandle unmapJava7Or8(MethodHandles.Lookup lookup) throws ReflectiveOperationException {
		/*
		 * "Compile" a MethodHandle that is roughly equivalent to the following lambda: (ByteBuffer buffer) -> { sun.misc.Cleaner cleaner = ((java.nio.DirectByteBuffer) byteBuffer).cleaner(); if
		 * (nonNull(cleaner)) cleaner.clean(); else noop(cleaner); // the noop is needed because MethodHandles#guardWithTest always needs both if and else }
		 */
		Class directBufferClass = Class.forName("java.nio.DirectByteBuffer");
		Method m = directBufferClass.getMethod("cleaner");
		m.setAccessible(true);
		MethodHandle directBufferCleanerMethod = lookup.unreflect(m);
		Class cleanerClass = directBufferCleanerMethod.type().returnType();
		MethodHandle cleanMethod = lookup.findVirtual(cleanerClass, "clean", methodType(void.class));
		MethodHandle nonNullTest = lookup.findStatic(MappedByteBuffers.class, "nonNull", methodType(boolean.class, Object.class)).asType(methodType(boolean.class, cleanerClass));
		MethodHandle noop = dropArguments(constant(Void.class, null).asType(methodType(void.class)), 0, cleanerClass);
		MethodHandle unmapper = filterReturnValue(directBufferCleanerMethod, guardWithTest(nonNullTest, cleanMethod, noop)).asType(methodType(void.class, ByteBuffer.class));
		return unmapper;
	}

	private static MethodHandle unmapJava9(MethodHandles.Lookup lookup) throws ReflectiveOperationException {
		Class unsafeClass = Class.forName("sun.misc.Unsafe");
		MethodHandle unmapper = lookup.findVirtual(unsafeClass, "invokeCleaner", methodType(void.class, ByteBuffer.class));
		Field f = unsafeClass.getDeclaredField("theUnsafe");
		f.setAccessible(true);
		Object theUnsafe = f.get(null);
		return unmapper.bindTo(theUnsafe);
	}
}