LockChecker.java :  » Code-Analyzer » findbugs-1.3.9 » edu » umd » cs » findbugs » ba » Java Open Source

/*
 * 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;
import edu.umd.cs.findbugs.classfile.CheckedAnalysisException;
import edu.umd.cs.findbugs.classfile.Global;
import edu.umd.cs.findbugs.classfile.MethodDescriptor;

/**
 * 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 MethodDescriptor methodDescriptor;
  private Method method;
  private LockDataflow lockDataflow;
  private ValueNumberDataflow vnaDataflow;
  private HashMap<Location, LockSet> cache;

  /**
   * Constructor.
   */
  public LockChecker(MethodDescriptor methodDescriptor) {
    this.cache = new HashMap<Location, LockSet>();
    this.methodDescriptor = methodDescriptor;
  }

  /**
   * Execute dataflow analyses (only if required).
   * @throws CheckedAnalysisException 
   */
  public void execute() throws CheckedAnalysisException {
    method = Global.getAnalysisCache().getMethodAnalysis(Method.class, methodDescriptor);
    ClassContext classContext = Global.getAnalysisCache().getClassAnalysis(ClassContext.class, methodDescriptor.getClassDescriptor());
    
    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;
    }
  }
}