gistfile1.txt

Synconrized(Scopes.class): 

public class Scopes {
    
    public static <T> T getObject(ScopeSource source, Class<T> clazz, ScopedBuilder<T> builder){
        T result = source.getScopedObject(clazz);
        if(result == null){
            synchronized (Scopes.class){
                result = source.getScopedObject(clazz);
                if(result == null){
                    result = source.putScopedObject(clazz, builder.build(source));
                }
            }
        }

        return result;
    }
}

vs on method parameter:

public class Scopes {
    
    public static <T> T getObject(ScopeSource source, Class<T> clazz, ScopedBuilder<T> builder){
        T result = source.getScopedObject(clazz);
        if(result == null){
            synchronized (source){
                result = source.getScopedObject(clazz);
                if(result == null){
                    result = source.putScopedObject(clazz, builder.build(source));
                }
            }
        }

        return result;
    }
}