01: ////////////////////////////////////////////////////////////////////////////////
02: // checkstyle: Checks Java source code for adherence to a set of rules.
03: // Copyright (C) 2001-2007 Oliver Burn
04: //
05: // This library is free software; you can redistribute it and/or
06: // modify it under the terms of the GNU Lesser General Public
07: // License as published by the Free Software Foundation; either
08: // version 2.1 of the License, or (at your option) any later version.
09: //
10: // This library is distributed in the hope that it will be useful,
11: // but WITHOUT ANY WARRANTY; without even the implied warranty of
12: // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13: // Lesser General Public License for more details.
14: //
15: // You should have received a copy of the GNU Lesser General Public
16: // License along with this library; if not, write to the Free Software
17: // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18: ////////////////////////////////////////////////////////////////////////////////
19: package com.puppycrawl.tools.checkstyle.checks.coding;
20:
21: import antlr.collections.AST;
22: import com.puppycrawl.tools.checkstyle.api.Check;
23: import com.puppycrawl.tools.checkstyle.api.DetailAST;
24: import com.puppycrawl.tools.checkstyle.api.TokenTypes;
25:
26: /**
27: * Detect the double-checked locking idiom, a technique that tries to avoid
28: * synchronization overhead but is incorrect because of subtle artifacts of
29: * the java memory model.
30: *
31: * See <a href=
32: * "http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html"
33: * >The "Double-Checked Locking is Broken" Declaration</a> for a
34: * more in depth explanation.
35: *
36: * @author Lars Kühne
37: */
38: public class DoubleCheckedLockingCheck extends Check {
39: /** {@inheritDoc} */
40: public int[] getDefaultTokens() {
41: return new int[] { TokenTypes.LITERAL_IF };
42: }
43:
44: /** {@inheritDoc} */
45: public void visitToken(DetailAST aAST) {
46: final DetailAST synchronizedAST = getLowestParent(aAST,
47: TokenTypes.LITERAL_SYNCHRONIZED);
48: if (synchronizedAST == null) {
49: return;
50: }
51:
52: final DetailAST ifAST = getLowestParent(synchronizedAST,
53: TokenTypes.LITERAL_IF);
54: if (ifAST == null) {
55: return;
56: }
57:
58: if (getIfCondition(aAST).equalsTree(getIfCondition(ifAST))) {
59: log(aAST.getLineNo(), aAST.getColumnNo(),
60: "doublechecked.locking.avoid");
61: }
62: }
63:
64: /**
65: * returns the condition of an if statement.
66: * @param aIfAST the LITERAL_IF AST
67: * @return the AST that represents the condition of the if statement
68: */
69: private AST getIfCondition(DetailAST aIfAST) {
70: return aIfAST.getFirstChild().getNextSibling();
71: }
72:
73: /**
74: * searches towards the root of the AST for a specific AST type.
75: * @param aAST the starting node for searching (inclusive)
76: * @param aTokenType the token type to search for
77: * @return the first token of type aTokenTye or null if no such token exists
78: */
79: private DetailAST getLowestParent(DetailAST aAST, int aTokenType) {
80: DetailAST synchronizedParent = aAST;
81: while ((synchronizedParent != null)
82: && (synchronizedParent.getType() != aTokenType)) {
83: synchronizedParent = synchronizedParent.getParent();
84: }
85: return synchronizedParent;
86: }
87: }
|