1 /* 2 * Copyright (c) 2001, 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. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 package sun.jvm.hotspot.utilities; 26 27 import sun.jvm.hotspot.debugger.*; 28 import sun.jvm.hotspot.gc.shared.*; 29 import sun.jvm.hotspot.memory.*; 30 import sun.jvm.hotspot.oops.*; 31 import sun.jvm.hotspot.runtime.*; 32 33 /** Helper class which covers the reserved area of the heap with an 34 (object-external) set of mark bits, used for GC-like scans through 35 the heap like liveness analysis. */ 36 37 public class MarkBits { 38 public MarkBits(CollectedHeap heap) { 39 MemRegion reserved = heap.reservedRegion(); 40 // Must cover "reserved" with one bit for each OopHandle 41 start = reserved.start(); 42 end = reserved.end(); 43 long numOopHandles = end.minus(start) / VM.getVM().getOopSize(); 44 // FIXME: will have trouble with larger heap sizes 45 bits = new BitMap((int) numOopHandles); 46 } 47 48 public void clear() { 49 bits.clear(); 50 } 51 52 /** Returns true if a mark was newly placed for the given Oop, or 53 false if the Oop was already marked. If the Oop happens to lie 54 outside the heap (should not happen), prints a warning and 55 returns false. */ 56 public boolean mark(Oop obj) { 57 if (obj == null) { 58 System.err.println("MarkBits: WARNING: null object, ignoring"); 59 return false; 60 } 61 62 OopHandle handle = obj.getHandle(); 63 // FIXME: will have trouble with larger heap sizes 64 long idx = handle.minus(start) / VM.getVM().getOopSize(); 65 if ((idx < 0) || (idx >= bits.size())) { 66 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring"); 67 return false; 68 } 69 int intIdx = (int) idx; 70 if (bits.at(intIdx)) { 71 return false; // already marked 72 } 73 bits.atPut(intIdx, true); 74 return true; 75 } 76 77 /** Forces clearing of a given mark bit. */ 78 public void clear(Oop obj) { 79 OopHandle handle = obj.getHandle(); 80 // FIXME: will have trouble with larger heap sizes 81 long idx = handle.minus(start) / VM.getVM().getOopSize(); 82 if ((idx < 0) || (idx >= bits.size())) { 83 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring"); 84 return; 85 } 86 int intIdx = (int) idx; 87 bits.atPut(intIdx, false); 88 } 89 90 private BitMap bits; 91 private Address start; 92 private Address end; 93 }