lockchecker.java

A static analysis tool to find bugs in Java programs

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2005, 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;

import java.util.BitSet;
import java.util.HashMap;

import org.apache.bcel.Constants;
import org.apache.bcel.classfile.Method;

import edu.umd.cs.findbugs.ba.vna.ValueNumber;
import edu.umd.cs.findbugs.ba.vna.ValueNumberDataflow;

/**
 * Front-end for LockDataflow that can avoid doing unnecessary work
 * (e.g., actually performing the lock dataflow)
 * if the method analyzed does not contain explicit
 * monitorenter/monitorexit instructions.
 * 
 * <p>Note that because LockSets use value numbers, ValueNumberAnalysis
 * must be performed for all methods that are synchronized or contain
 * explicit monitorenter/monitorexit instructions.</p>
 * 
 * @see LockSet
 * @see LockDataflow
 * @see LockAnalysis
 * @author David Hovemeyer
 */
public class LockChecker {
	private ClassContext classContext;
	private Method method;
	private LockDataflow lockDataflow;
	private ValueNumberDataflow vnaDataflow;
	private HashMap<Location, LockSet> cache;

	/**
	 * Constructor.
	 * 
	 * @param classContext ClassContext for the class
	 * @param method       Method we want LockSets for
	 */
	public LockChecker(ClassContext classContext, Method method) {
		this.classContext = classContext;
		this.method = method;
		this.cache = new HashMap<Location, LockSet>();
	}

	/**
	 * Execute dataflow analyses (only if required).
	 * 
	 * @throws DataflowAnalysisException
	 * @throws CFGBuilderException
	 */
	public void execute() throws DataflowAnalysisException, CFGBuilderException {
		BitSet bytecodeSet = classContext.getBytecodeSet(method);
		if (bytecodeSet == null) return;
		if (bytecodeSet.get(Constants.MONITORENTER) || bytecodeSet.get(Constants.MONITOREXIT)) {
			this.lockDataflow = classContext.getLockDataflow(method);
		} else if (method.isSynchronized()) {
			this.vnaDataflow = classContext.getValueNumberDataflow(method); // will need this later
		}
	}

	/**
	 * Get LockSet at given Location.
	 * 
	 * @param location the Location
	 * @return         the LockSet at that Location
	 * @throws DataflowAnalysisException
	 */
	public LockSet getFactAtLocation(Location location) throws DataflowAnalysisException {
		if (lockDataflow != null)
			return lockDataflow.getFactAtLocation(location);
		else {
			LockSet lockSet = cache.get(location);
			if (lockSet == null) {
				lockSet = new LockSet();
				lockSet.setDefaultLockCount(0);
				if (method.isSynchronized() && !method.isStatic()) {
					// LockSet contains just the "this" reference
					ValueNumber instance = vnaDataflow.getAnalysis().getThisValue();
					lockSet.setLockCount(instance.getNumber(), 1);
				} else {
					// LockSet is completely empty - nothing to do
				}
				cache.put(location, lockSet);
			}
			return lockSet;
		}
	}
}