/*
 * Copyright (c) 2009, 2012, 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 com.oracle.graal.nodes.java;

import com.oracle.max.cri.ci.*;
import com.oracle.graal.nodes.*;
import com.oracle.graal.nodes.extended.*;
import com.oracle.graal.nodes.type.*;

/**
 * The {@code AccessMonitorNode} is the base class of both monitor acquisition and release.
 * <br>
 * The VM needs information about monitors in the debug information. This information is built from
 * the nesting level of {@link MonitorEnterNode} when the LIR is constructed. Therefore, monitor
 * nodes must not be removed from the graph unless it is guaranteed that the nesting level does not change.
 * For example, you must not remove a {@link MonitorEnterNode} for a thread-local object or for a recursive locking.
 * Instead, mark the node as {@link #eliminated}. This makes sure that the meta data still contains the complete
 * locking hierarchy.
 * <br>
 * The Java bytecode specification allows non-balanced locking. Graal does not handle such cases and throws a
 * {@link CiBailout} instead. Detecting non-balanced monitors during bytecode parsing is difficult, since the
 * node flowing into the {@link MonitorExitNode} can be a phi function hiding the node that was flowing into the
 * {@link MonitorEnterNode}. Optimization phases are free to throw {@link CiBailout} if they detect such cases.
 * Otherwise, they are detected during LIR construction.
 */
public abstract class AccessMonitorNode extends AbstractStateSplit implements MemoryCheckpoint {

    @Input private ValueNode object;
    @Data private boolean eliminated;

    public ValueNode object() {
        return object;
    }

    public boolean eliminated() {
        return eliminated;
    }

    public void eliminate() {
        eliminated = true;
    }

    /**
     * Creates a new AccessMonitor instruction.
     *
     * @param object the instruction producing the object
     */
    public AccessMonitorNode(ValueNode object) {
        super(StampFactory.illegal());
        this.object = object;
    }
}