/*
* Copyright 2014 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.errorprone.bugpatterns.threadsafety;
import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.MaturityLevel.MATURE;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.SynchronizedTree;
import com.sun.tools.javac.code.Flags;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.tree.JCTree.JCExpression;
import com.sun.tools.javac.tree.TreeInfo;
/**
* @author cushon@google.com (Liam Miller-Cushon)
*/
@BugPattern(name = "SynchronizeOnNonFinalField",
summary = "Synchronizing on non-final fields is not safe: if the field is ever updated,"
+ " different threads may end up locking on different objects.",
explanation = "Possible fixes:\n"
+ "* If the field is already effectively final, add the missing 'final' modifier.\n"
+ "* If the field needs to be mutable, create a separate lock by adding a private"
+ " final field and synchronizing on it to guard all accesses.",
category = JDK, severity = WARNING, maturity = MATURE)
public class SynchronizeOnNonFinalField extends BugChecker
implements BugChecker.SynchronizedTreeMatcher {
@Override
public Description matchSynchronized(SynchronizedTree tree, VisitorState state) {
Symbol symbol = ASTHelpers.getSymbol(TreeInfo.skipParens((JCExpression) tree.getExpression()));
if (!(symbol instanceof VarSymbol)) {
return Description.NO_MATCH;
}
// TODO(user): check that the receiver doesn't contain mutable state.
// Currently 'this.locks[i].mu' is accepted if 'mu' is final but 'locks' is non-final.
VarSymbol varSymbol = (VarSymbol) symbol;
if (varSymbol.isLocal()
|| varSymbol.isStatic()
|| (varSymbol.flags() & Flags.FINAL) != 0) {
return Description.NO_MATCH;
}
return describeMatch(tree.getExpression());
}
}