How to protect dynamic lookup content when it is changing?

i would like to block accesing lookup content when another thread is puting into lookup.
here is an example


Code:

public class MyNode extends AbstractNode {

    private InstanceContent instanceContent = new InstanceContent();

    public MyNode(SomeKey key) {
        this(key, new InstanceContent());
    }

    private CarNode(SomeKey key, InstanceContent ic) {
        super(Children.LEAF, new AbstractLookup(ic));

        this.instanceContent = ic;
        instanceContent.add(key);
    }
    
    public void setNewKey(SomeKey key) {
        Collection<? extends SomeKey> lookupAll = getLookup().lookupAll(SomeKey.class);
        for (Object item : lookupAll) {
            remove(item);
        }

 //at this time lookup is empty, if another thread tries to get content, it gets null
        
        instanceContent.add(key);
    }
}
}




is there an elegant way to block getLookup().lookup(SomeKey.class) during execution of setNewKey()?