| /* |
| * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| package jdk.vm.ci.hotspot; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.ReferenceQueue; |
| import java.lang.ref.WeakReference; |
| import java.util.Arrays; |
| import java.util.Iterator; |
| import java.util.Map; |
| import java.util.WeakHashMap; |
| |
| import jdk.vm.ci.meta.JavaKind; |
| import jdk.vm.ci.meta.ResolvedJavaType; |
| |
| /** |
| * This class manages the set of metadata roots that must be scanned during garbage collection. |
| * Because of class redefinition Method* and ConstantPool* can be freed if they don't appear to be |
| * in use so they must be tracked when there are live references to them from Java. |
| * |
| * The general theory of operation is that all {@link MetaspaceWrapperObject}s are created by |
| * calling into the VM which calls back out to actually create the wrapper instance. During the call |
| * the VM keeps the metadata reference alive through the use of metadata handles. Once the call |
| * completes the wrapper object is registered here and will be scanned during metadata scanning. The |
| * weakness of the reference to the wrapper object allows them to be reclaimed when they are no |
| * longer used. |
| * |
| */ |
| public class HotSpotJVMCIMetaAccessContext { |
| |
| /** |
| * The set of currently live contexts used for tracking of live metadata. Examined from the VM |
| * during garbage collection. |
| */ |
| private static WeakReference<?>[] allContexts = new WeakReference<?>[0]; |
| |
| /** |
| * This is a chunked list of metadata roots. It can be read from VM native code so it's been |
| * marked volatile to ensure the order of updates are respected. |
| */ |
| private volatile Object[] metadataRoots; |
| |
| private ChunkedList<WeakReference<MetaspaceWrapperObject>> list = new ChunkedList<>(); |
| |
| /** |
| * The number of weak references freed since the last time the list was shrunk. |
| */ |
| private int freed; |
| |
| /** |
| * The {@link ReferenceQueue} tracking the weak references created by this context. |
| */ |
| private final ReferenceQueue<MetaspaceWrapperObject> queue = new ReferenceQueue<>(); |
| |
| static synchronized void add(HotSpotJVMCIMetaAccessContext context) { |
| for (int i = 0; i < allContexts.length; i++) { |
| if (allContexts[i] == null || allContexts[i].get() == null) { |
| allContexts[i] = new WeakReference<>(context); |
| return; |
| } |
| } |
| int index = allContexts.length; |
| allContexts = Arrays.copyOf(allContexts, index + 2); |
| allContexts[index] = new WeakReference<>(context); |
| } |
| |
| HotSpotJVMCIMetaAccessContext() { |
| add(this); |
| } |
| |
| /** |
| * Periodically trim the list of tracked metadata. A new list is created to replace the old to |
| * avoid concurrent scanning issues. |
| */ |
| private void clean() { |
| Reference<?> ref = queue.poll(); |
| if (ref == null) { |
| return; |
| } |
| while (ref != null) { |
| freed++; |
| ref = queue.poll(); |
| } |
| if (freed > list.size() / 2) { |
| ChunkedList<WeakReference<MetaspaceWrapperObject>> newList = new ChunkedList<>(); |
| for (WeakReference<MetaspaceWrapperObject> element : list) { |
| /* |
| * The referent could become null anywhere in here but it doesn't matter. It will |
| * get cleaned up next time. |
| */ |
| if (element != null && element.get() != null) { |
| newList.add(element); |
| } |
| } |
| list = newList; |
| metadataRoots = list.getHead(); |
| freed = 0; |
| } |
| } |
| |
| /** |
| * Add a {@link MetaspaceWrapperObject} to tracked by the GC. It's assumed that the caller is |
| * responsible for keeping the reference alive for the duration of the call. Once registration |
| * is complete then the VM will ensure it's kept alive. |
| * |
| * @param metaspaceObject |
| */ |
| |
| public synchronized void add(MetaspaceWrapperObject metaspaceObject) { |
| clean(); |
| list.add(new WeakReference<>(metaspaceObject, queue)); |
| if (list.getHead() != metadataRoots) { |
| /* |
| * The list enlarged so update the head. |
| */ |
| metadataRoots = list.getHead(); |
| } |
| assert isRegistered(metaspaceObject); |
| } |
| |
| protected ResolvedJavaType createClass(Class<?> javaClass) { |
| if (javaClass.isPrimitive()) { |
| JavaKind kind = JavaKind.fromJavaClass(javaClass); |
| return new HotSpotResolvedPrimitiveType(kind); |
| } else { |
| return new HotSpotResolvedObjectTypeImpl(javaClass, this); |
| } |
| } |
| |
| private final Map<Class<?>, WeakReference<ResolvedJavaType>> typeMap = new WeakHashMap<>(); |
| |
| /** |
| * Gets the JVMCI mirror for a {@link Class} object. |
| * |
| * @return the {@link ResolvedJavaType} corresponding to {@code javaClass} |
| */ |
| public synchronized ResolvedJavaType fromClass(Class<?> javaClass) { |
| WeakReference<ResolvedJavaType> typeRef = typeMap.get(javaClass); |
| ResolvedJavaType type = typeRef != null ? typeRef.get() : null; |
| if (type == null) { |
| type = createClass(javaClass); |
| typeMap.put(javaClass, new WeakReference<>(type)); |
| } |
| return type; |
| } |
| |
| /** |
| * A very simple append only chunked list implementation. |
| */ |
| static class ChunkedList<T> implements Iterable<T> { |
| private static final int CHUNK_SIZE = 32; |
| |
| private static final int NEXT_CHUNK_INDEX = CHUNK_SIZE - 1; |
| |
| private Object[] head; |
| private int index; |
| private int size; |
| |
| ChunkedList() { |
| head = new Object[CHUNK_SIZE]; |
| index = 0; |
| } |
| |
| void add(T element) { |
| if (index == NEXT_CHUNK_INDEX) { |
| Object[] newHead = new Object[CHUNK_SIZE]; |
| newHead[index] = head; |
| head = newHead; |
| index = 0; |
| } |
| head[index++] = element; |
| size++; |
| } |
| |
| Object[] getHead() { |
| return head; |
| } |
| |
| public Iterator<T> iterator() { |
| return new ChunkIterator<>(); |
| } |
| |
| int size() { |
| return size; |
| } |
| |
| class ChunkIterator<V> implements Iterator<V> { |
| |
| ChunkIterator() { |
| currentChunk = head; |
| currentIndex = -1; |
| next = findNext(); |
| } |
| |
| Object[] currentChunk; |
| int currentIndex; |
| V next; |
| |
| @SuppressWarnings("unchecked") |
| V findNext() { |
| V result; |
| do { |
| currentIndex++; |
| if (currentIndex == NEXT_CHUNK_INDEX) { |
| currentChunk = (Object[]) currentChunk[currentIndex]; |
| currentIndex = 0; |
| if (currentChunk == null) { |
| return null; |
| } |
| } |
| result = (V) currentChunk[currentIndex]; |
| } while (result == null); |
| return result; |
| } |
| |
| public boolean hasNext() { |
| return next != null; |
| } |
| |
| public V next() { |
| V result = next; |
| next = findNext(); |
| return result; |
| } |
| |
| } |
| |
| } |
| |
| synchronized boolean isRegistered(MetaspaceWrapperObject wrapper) { |
| for (WeakReference<MetaspaceWrapperObject> m : list) { |
| if (m != null && m.get() == wrapper) { |
| return true; |
| } |
| } |
| return false; |
| } |
| } |