1 /* 2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.ref; 27 28 29 import java.util.Map; 30 import java.util.HashMap; 31 import java.util.Arrays; 32 import java.util.Comparator; 33 34 /** 35 * This FinalizerHistogram class is for GC.finalizer_info diagnostic command support. 36 * It is invoked by the VM. 37 */ 38 39 final class FinalizerHistogram { 40 41 private static final class Entry { 42 private int instanceCount; 43 private final String className; 44 45 int getInstanceCount() { 46 return instanceCount; 47 } 48 49 void increment() { 50 instanceCount += 1; 51 } 52 53 Entry(String className) { 54 this.className = className; 55 } 56 } 57 58 // Method below is called by VM and VM expect certain 59 // entry class layout. 60 61 static Entry[] getFinalizerHistogram() { 62 Map<String, Entry> countMap = new HashMap<>(); 63 ReferenceQueue<Object> queue = Finalizer.getQueue(); 64 queue.forEach(r -> { 65 Object referent = r.get(); 66 if (referent != null) { 67 countMap.computeIfAbsent( 68 referent.getClass().getName(), Entry::new).increment(); 69 /* Clear stack slot containing this variable, to decrease 70 the chances of false retention with a conservative GC */ 71 referent = null; 72 } 73 }); 74 75 Entry[] fhe = countMap.values().toArray(new Entry[countMap.size()]); 76 Arrays.sort(fhe, 77 Comparator.comparingInt(Entry::getInstanceCount).reversed()); 78 return fhe; 79 } 80 }