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 }