False Positive : Non-double-checked pattern is reported as `DoubleCheckedLocking`

[Carlson-JLQ]

False Positive : Non-double-checked pattern is reported as DoubleCheckedLocking

Affects errorprone Version:

2.48.0

Checker:

DoubleCheckedLocking

Description:

The official DoubleCheckedLocking bug pattern targets the classic lazy-initialization shape: an outer null check, a synchronized block, and an inner null check on the same non-volatile field. This test case does not follow that pattern because the outer condition is f != null, not f == null.

Code Sample demonstrating the issue:

public class NegCase2 {
    private Object f;

    public void method() {
        if (f != null) {
            synchronized (this) {
                if (f == null) {
                    f = new Object();
                }
            }
        }
    }
}

This code is inconsistent and suspicious in its own way, but it is not the canonical double-checked locking pattern described by Error Prone. The bug pattern documentation specifically talks about unsafe lazy initialization with repeated null checks on a non-volatile field.

Expected outcome:

Error Prone should not report DoubleCheckedLocking for this code, but it does. This is a false-positive.

[chrswk]

Using 2.48.0 this example does not trigger any bug patterns.