#1471 [java] DoubleCheckedLocking: False positives

[Alix Warnke]

The rule triggers on the following implementation (in a Java7 codebase):

private static volatile Foo instance;

public static Foo getInstance() {
    Foo result = instance;
    if (result == null) {
        synchronized (Foo.class) {
            result = instance;
            if (result == null) {
                result = instance = new Foo();
            }
        }
    }
    return result;
}

This implementation should be OK for JDK 5+ according to: http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html (section "Under the new Java Memory Model")

[Andreas Dangel]

See also: https://sourceforge.net/p/pmd/bugs/884/

[Andreas Dangel]

As a workaround, you can get rid of the false positive by avoiding to use a local variable ("result"), until the next pmd release.

This bug will be fixed with PMD 5.3.7, 5.4.2 and 5.5.0.

Commit: https://github.com/pmd/pmd/commit/cb5ac3086e4d33c50c1bb91ca0a9971429327bd7