////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2008 Oliver Burn
//
// 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 com.puppycrawl.tools.checkstyle.checks.coding;
import antlr.collections.AST;
import com.puppycrawl.tools.checkstyle.api.Check;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
/**
* Detect the double-checked locking idiom, a technique that tries to avoid
* synchronization overhead but is incorrect because of subtle artifacts of
* the java memory model.
*
* See <a href=
* "http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html"
* >The "Double-Checked Locking is Broken" Declaration</a> for a
* more in depth explanation.
*
* @author Lars Kühne
*/
public class DoubleCheckedLockingCheck extends Check
{
@Override
public int[] getDefaultTokens()
{
return new int[]{TokenTypes.LITERAL_IF};
}
@Override
public void visitToken(DetailAST aAST)
{
final DetailAST synchronizedAST =
getLowestParent(aAST, TokenTypes.LITERAL_SYNCHRONIZED);
if (synchronizedAST == null) {
return;
}
final DetailAST ifAST =
getLowestParent(synchronizedAST, TokenTypes.LITERAL_IF);
if (ifAST == null) {
return;
}
if (getIfCondition(aAST).equalsTree(getIfCondition(ifAST))) {
log(aAST.getLineNo(), aAST.getColumnNo(),
"doublechecked.locking.avoid");
}
}
/**
* returns the condition of an if statement.
* @param aIfAST the LITERAL_IF AST
* @return the AST that represents the condition of the if statement
*/
private AST getIfCondition(DetailAST aIfAST)
{
return aIfAST.getFirstChild().getNextSibling();
}
/**
* searches towards the root of the AST for a specific AST type.
* @param aAST the starting node for searching (inclusive)
* @param aTokenType the token type to search for
* @return the first token of type aTokenTye or null if no such token exists
*/
private DetailAST getLowestParent(DetailAST aAST, int aTokenType)
{
DetailAST synchronizedParent = aAST;
while ((synchronizedParent != null)
&& (synchronizedParent.getType() != aTokenType))
{
synchronizedParent = synchronizedParent.getParent();
}
return synchronizedParent;
}
}