/*
 * Copyright (c) 2001, 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 sun.jvm.hotspot.utilities;

import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.gc.shared.*;
import sun.jvm.hotspot.memory.*;
import sun.jvm.hotspot.oops.*;
import sun.jvm.hotspot.runtime.*;

Helper class which covers the reserved area of the heap with an (object-external) set of mark bits, used for GC-like scans through the heap like liveness analysis.
/** Helper class which covers the reserved area of the heap with an (object-external) set of mark bits, used for GC-like scans through the heap like liveness analysis. */
public class MarkBits { public MarkBits(CollectedHeap heap) { MemRegion reserved = heap.reservedRegion(); // Must cover "reserved" with one bit for each OopHandle start = reserved.start(); end = reserved.end(); long numOopHandles = end.minus(start) / VM.getVM().getOopSize(); // FIXME: will have trouble with larger heap sizes bits = new BitMap((int) numOopHandles); } public void clear() { bits.clear(); }
Returns true if a mark was newly placed for the given Oop, or false if the Oop was already marked. If the Oop happens to lie outside the heap (should not happen), prints a warning and returns false.
/** Returns true if a mark was newly placed for the given Oop, or false if the Oop was already marked. If the Oop happens to lie outside the heap (should not happen), prints a warning and returns false. */
public boolean mark(Oop obj) { if (obj == null) { System.err.println("MarkBits: WARNING: null object, ignoring"); return false; } OopHandle handle = obj.getHandle(); // FIXME: will have trouble with larger heap sizes long idx = handle.minus(start) / VM.getVM().getOopSize(); if ((idx < 0) || (idx >= bits.size())) { System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring"); return false; } int intIdx = (int) idx; if (bits.at(intIdx)) { return false; // already marked } bits.atPut(intIdx, true); return true; }
Forces clearing of a given mark bit.
/** Forces clearing of a given mark bit. */
public void clear(Oop obj) { OopHandle handle = obj.getHandle(); // FIXME: will have trouble with larger heap sizes long idx = handle.minus(start) / VM.getVM().getOopSize(); if ((idx < 0) || (idx >= bits.size())) { System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring"); return; } int intIdx = (int) idx; bits.atPut(intIdx, false); } private BitMap bits; private Address start; private Address end; }