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1 /*
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2 * Copyright 2001-2003 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 package sun.jvm.hotspot.utilities;
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26
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27 import sun.jvm.hotspot.debugger.*;
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28 import sun.jvm.hotspot.gc_interface.*;
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29 import sun.jvm.hotspot.memory.*;
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30 import sun.jvm.hotspot.oops.*;
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31 import sun.jvm.hotspot.runtime.*;
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32
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33 /** Helper class which covers the reserved area of the heap with an
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34 (object-external) set of mark bits, used for GC-like scans through
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35 the heap like liveness analysis. */
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36
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37 public class MarkBits {
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38 public MarkBits(CollectedHeap heap) {
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39 MemRegion reserved = heap.reservedRegion();
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40 // Must cover "reserved" with one bit for each OopHandle
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41 start = reserved.start();
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42 end = reserved.end();
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43 long numOopHandles = end.minus(start) / VM.getVM().getOopSize();
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44 // FIXME: will have trouble with larger heap sizes
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45 bits = new BitMap((int) numOopHandles);
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46 }
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47
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48 public void clear() {
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49 bits.clear();
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50 }
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51
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52 /** Returns true if a mark was newly placed for the given Oop, or
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53 false if the Oop was already marked. If the Oop happens to lie
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54 outside the heap (should not happen), prints a warning and
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55 returns false. */
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56 public boolean mark(Oop obj) {
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57 if (obj == null) {
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58 System.err.println("MarkBits: WARNING: null object, ignoring");
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59 return false;
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60 }
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61
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62 OopHandle handle = obj.getHandle();
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63 // FIXME: will have trouble with larger heap sizes
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64 long idx = handle.minus(start) / VM.getVM().getOopSize();
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65 if ((idx < 0) || (idx >= bits.size())) {
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66 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring");
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67 return false;
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68 }
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69 int intIdx = (int) idx;
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70 if (bits.at(intIdx)) {
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71 return false; // already marked
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72 }
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73 bits.atPut(intIdx, true);
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74 return true;
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75 }
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76
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77 /** Forces clearing of a given mark bit. */
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78 public void clear(Oop obj) {
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79 OopHandle handle = obj.getHandle();
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80 // FIXME: will have trouble with larger heap sizes
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81 long idx = handle.minus(start) / VM.getVM().getOopSize();
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82 if ((idx < 0) || (idx >= bits.size())) {
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83 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring");
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84 return;
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85 }
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86 int intIdx = (int) idx;
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87 bits.atPut(intIdx, false);
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88 }
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89
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90 private BitMap bits;
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91 private Address start;
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92 private Address end;
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93 }
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