Visibility of mutable object under different locks in Java

mFeaute is a mutable object.

I want to know if the change of mFeature in setFeature(Feature feature) is visible to mFeature in useFeature(…) with a different explicit form of synchronized.

Thanks.

public class FeatureService {
    private static Feature mFeature= null; 
    private final Object MUTEX = new Object();
    ...

    static void setFeature(Feature feature){
        // doSomething
        synchronized (FeatureService.class){
            mFeature = feature;
            // doSomething
        }
        // doSomething
    }

    public void useFeature(...){
        // doSomething
        synchronized (MUTEX){
            someFunction(mFeature);
            // doSomething 
        }
        // doSomething
    }
}
}

Answer

The above code is suffering from a data race and hence is broken. You do not have a happens before edge between the write and the read of mfeature because different locks are used. You need to use the same lock instance for both reading and writing.