hotspot/src/jdk.internal.vm.ci/share/classes/jdk.vm.ci.hotspot/src/jdk/vm/ci/hotspot/HotSpotJVMCIMetaAccessContext.java - platform/libcore - Git at Google

 /*
  * 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 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 ClassValue<WeakReference<ResolvedJavaType>> resolvedJavaType = new ClassValue<WeakReference<ResolvedJavaType>>() {
         @Override
         protected WeakReference<ResolvedJavaType> computeValue(Class<?> type) {
             return new WeakReference<>(createClass(type));
         }
     };

     /**
      * Gets the JVMCI mirror for a {@link Class} object.
      *
      * @return the {@link ResolvedJavaType} corresponding to {@code javaClass}
      */
     public ResolvedJavaType fromClass(Class<?> javaClass) {
         ResolvedJavaType javaType = null;
         while (javaType == null) {
             WeakReference<ResolvedJavaType> type = resolvedJavaType.get(javaClass);
             javaType = type.get();
             if (javaType == null) {
                 /*
                  * If the referent has become null, clear out the current value
                  * and let computeValue above create a new value.  Reload the
                  * value in a loop because in theory the WeakReference referent
                  * can be reclaimed at any point.
                  */
                 resolvedJavaType.remove(javaClass);
             }
         }
         return javaType;
     }

     /**
      * 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;
     }
 }
	/*
	* 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 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 ClassValue<WeakReference<ResolvedJavaType>> resolvedJavaType = new ClassValue<WeakReference<ResolvedJavaType>>() {
	@Override
	protected WeakReference<ResolvedJavaType> computeValue(Class<?> type) {
	return new WeakReference<>(createClass(type));
	}
	};

	/**
	* Gets the JVMCI mirror for a {@link Class} object.
	*
	* @return the {@link ResolvedJavaType} corresponding to {@code javaClass}
	*/
	public ResolvedJavaType fromClass(Class<?> javaClass) {
	ResolvedJavaType javaType = null;
	while (javaType == null) {
	WeakReference<ResolvedJavaType> type = resolvedJavaType.get(javaClass);
	javaType = type.get();
	if (javaType == null) {
	/*
	* If the referent has become null, clear out the current value
	* and let computeValue above create a new value. Reload the
	* value in a loop because in theory the WeakReference referent
	* can be reclaimed at any point.
	*/
	resolvedJavaType.remove(javaClass);
	}
	}
	return javaType;
	}

	/**
	* 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;
	}
	}