FindSpinLoop.java

/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 2003-2005 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.detect;

import org.apache.bcel.classfile.Method;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.FieldAnnotation;
import edu.umd.cs.findbugs.StatelessDetector;
import edu.umd.cs.findbugs.SystemProperties;

public class FindSpinLoop extends BytecodeScanningDetector implements StatelessDetector {
    private static final boolean DEBUG = SystemProperties.getBoolean("findspinloop.debug");

    int stage = 0;

    int start;

    private BugReporter bugReporter;

    private FieldAnnotation lastFieldSeen;

    public FindSpinLoop(BugReporter bugReporter) {
        this.bugReporter = bugReporter;
    }

    @Override
    public void visit(Method obj) {
        if (DEBUG)
            System.out.println("Saw " + getFullyQualifiedMethodName());
        stage = 0;
    }

    @Override
    public void sawOpcode(int seen) {

        // System.out.println("PC: " + PC + ", stage: " + stage1);
        switch (seen) {
        case ALOAD_0:
        case ALOAD_1:
        case ALOAD_2:
        case ALOAD_3:
        case ALOAD:
            if (DEBUG)
                System.out.println("   ALOAD at PC " + getPC());
            start = getPC();
            stage = 1;
            break;
        case GETSTATIC:
            if (DEBUG)
                System.out.println("   getfield in stage " + stage);
            lastFieldSeen = FieldAnnotation.fromReferencedField(this);
            start = getPC();
            stage = 2;
            break;
        case GETFIELD:
            if (DEBUG)
                System.out.println("   getfield in stage " + stage);
            lastFieldSeen = FieldAnnotation.fromReferencedField(this);
            if (stage == 1 || stage == 2) {
                stage = 2;
            } else
                stage = 0;
            break;
        case GOTO:
        case IFNE:
        case IFEQ:
        case IFNULL:
        case IFNONNULL:
            if (DEBUG)
                System.out.println("   conditional branch in stage " + stage + " to " + getBranchTarget());
            if (stage == 2 && getBranchTarget() == start) {
                bugReporter.reportBug(new BugInstance(this, "SP_SPIN_ON_FIELD", NORMAL_PRIORITY).addClassAndMethod(this)
                        .addReferencedField(lastFieldSeen).addSourceLine(this, start));
                stage = 0;
            } else if (getBranchTarget() < getPC())
                stage = 0;
            break;
        default:
            stage = 0;
            break;
        }

    }
}