Yes, you're right.  I should have tried it before suggesting it.  The problem is that getLastModified() is called to determine if dependencies need to be processed/validated, so it can't block before this has been done.  

The problem you're trying to avoid is the situation where DependencyList starts processing the dependencies for a module before the dependency map is finished initializing.  This can by done by adding a call to aggr.getDependencies().getDeclaredDependencies("require"); before the initial call to aggr.getDependencies().getLastModified().  The call to getDeclaredDependencies() will block until dependencies have been initialized/validated, and then the subsequent call to getLastModified() will return the up-to-date time stamp for the dependencies and won't have changed by the time getLastModified() is called again at the end of DependencyList.initialize();