/*
 * $Id$
 *
 * Copyright (C) 2003-2015 JNode.org
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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 Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; If not, write to the Free Software Foundation, Inc., 
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
package org.jnode.vm.memmgr.def;

import org.jnode.vm.VmMagic;
import org.jnode.annotation.MagicPermission;
import org.jnode.vm.classmgr.ObjectFlags;
import org.jnode.vm.facade.VmWriteBarrier;
import org.jnode.vm.memmgr.HeapHelper;
import org.jnode.vm.objects.VmSystemObject;
import org.vmmagic.pragma.UninterruptiblePragma;

/**
 * @author Ewout Prangsma (epr@users.sourceforge.net)
 */
@MagicPermission
final class DefaultWriteBarrier extends VmSystemObject implements VmWriteBarrier {

    /**
     * The heap helper
     */
    private final HeapHelper helper;

    /**
     * Is the write barrier active?
     */
    private boolean active;

    /**
     * Are there any object colors changed by the write barrier, since the last
     * reset
     */
    private boolean changed;

    private int arrayCopyCount;

    private int arrayStoreCount;

    private int putFieldCount;

    private int putStaticCount;

    /**
     * Initialize this instance.
     */
    public DefaultWriteBarrier(HeapHelper helper) {
        this.helper = helper;
    }

    /**
     * @see org.jnode.vm.facade.VmWriteBarrier#arrayCopyWriteBarrier(java.lang.Object[],
     *      int, int)
     */
    public final void arrayCopyWriteBarrier(Object array, int start, int end)
        throws UninterruptiblePragma {
        // The source array is already reachable, so by definition, all
        // entries will be reachable.
        // So we do nothing here
        arrayCopyCount++;
    }

    /**
     * @see org.jnode.vm.facade.VmWriteBarrier#arrayStoreWriteBarrier(java.lang.Object,
     *      int, java.lang.Object)
     */
    public final void arrayStoreWriteBarrier(Object ref, int index, Object value)
        throws UninterruptiblePragma {
        if (active) {
            shade(value);
        }
        arrayStoreCount++;
    }

    /**
     * @see org.jnode.vm.facade.VmWriteBarrier#putfieldWriteBarrier(java.lang.Object,
     *      int, java.lang.Object)
     */
    public final void putfieldWriteBarrier(Object ref, int offset, Object value)
        throws UninterruptiblePragma {
        if (active) {
            shade(value);
        }
        putFieldCount++;
    }

    /**
     * @see org.jnode.vm.facade.VmWriteBarrier#putstaticWriteBarrier(boolean, int,
     *      java.lang.Object)
     */
    public final void putstaticWriteBarrier(boolean shared, int staticsIndex, Object value)
        throws UninterruptiblePragma {
        if (active) {
            shade(value);
        }
        putStaticCount++;
    }

    /**
     * Set the GC color of the given value to gray if it is white.
     *
     * @param value
     */
    private final void shade(Object value) throws UninterruptiblePragma {
        if (value != null) {
            while (true) {
                final int gcColor = VmMagic.getObjectColor(value);
                if (gcColor > ObjectFlags.GC_WHITE) {
                    // Not white or yellow, we're done
                    return;
                }
                if (helper.atomicChangeObjectColor(value, gcColor,
                    ObjectFlags.GC_GREY)) {
                    // Change to grey, we're done
                    changed = true;
                    return;
                }
            }
        }
    }

    public String toString() {
        return "arrayCopy: " + arrayCopyCount + ", arrayStore: "
            + arrayStoreCount + ", putField: " + putFieldCount
            + ", putStatic: " + putStaticCount;
    }

    /**
     * @param active The active to set.
     */
    final void setActive(boolean active) {
        this.changed = false;
        this.active = active;
    }

    /**
     * @return Returns the changed.
     */
    final boolean isChanged() {
        return this.changed;
    }

    /**
     * Reset the changed attribute to false.
     */
    final void resetChanged() {
        this.changed = false;
    }
}