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/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003,2004 University of Maryland
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.ba.bcp;

import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MONITORENTER;

import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.vna.ValueNumberFrame;

/**
 * A PatternElement for matching a MONITORENTER instruction.
 *
 * @author DavidHovemeyer
 */
public class Monitorenter extends OneVariableInstruction {
    /**
     * Constructor.
     *
     * @param varName
     *            name of the variable representing the reference to the object
     *            being locked
     */
    public Monitorenter(String varName) {
        super(varName);
    }

    @Override
    public MatchResult match(InstructionHandle handle, ConstantPoolGen cpg, ValueNumberFrame before, ValueNumberFrame after,
            BindingSet bindingSet) throws DataflowAnalysisException {

        // Instruction must be MONITORENTER.
        Instruction ins = handle.getInstruction();
        if (!(ins instanceof MONITORENTER)) {
            return null;
        }

        // Ensure the object being locked matches any previous
        // instructions which bound our variable name to a value.
        Variable lock = new LocalVariable(before.getTopValue());
        return addOrCheckDefinition(lock, bindingSet);
    }
}