gianm commented on a change in pull request #7466: Java 9 compatible ByteBuffer
unmap operation
URL: https://github.com/apache/incubator-druid/pull/7466#discussion_r275128857
##########
File path:
core/src/main/java/org/apache/druid/java/util/common/ByteBufferUtils.java
##########
@@ -19,16 +19,124 @@
package org.apache.druid.java.util.common;
-import sun.misc.Cleaner;
-import sun.nio.ch.DirectBuffer;
+import org.apache.druid.utils.JvmUtils;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
/**
*/
public class ByteBufferUtils
{
+ // the following MethodHandle lookup code is adapted from Apache Kafka
+ //
https://github.com/apache/kafka/blob/e554dc518eaaa0747899e708160275f95c4e525f/clients/src/main/java/org/apache/kafka/common/utils/MappedByteBuffers.java
+
+ // 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 static void clean(ByteBuffer buffer)
+ {
+ if (!buffer.isDirect()) {
+ throw new IllegalArgumentException("Unmapping only works with direct
buffers");
+ }
+ if (UNMAP == null) {
+ throw UNMAP_NOT_SUPPORTED_EXCEPTION;
+ }
+
+ try {
+ UNMAP.invokeExact(buffer);
+ }
+ catch (Throwable throwable) {
+ throw new RuntimeException("Unable to unmap the mapped buffer",
throwable);
+ }
+ }
+
+ private static MethodHandle lookupUnmapMethodHandle()
+ {
+ final MethodHandles.Lookup lookup = MethodHandles.lookup();
+ try {
+ if (JvmUtils.isIsJava9Compatible()) {
+ 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 Druid 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);
Review comment:
setAccessible only affects this `Method` instance, not the actual method
itself, so it should be ok. i.e. if someone else, later on, does
`Class.forName("java.nio.DirectByteBuffer").getMethod("cleaner")` then that
Method will still start out non-accessible.
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