At present private resources will be downloaded in parallel only if multiple containers request the same resource. However otherwise it will be serial. The protocol between PrivateLocalizer and ContainerLocalizer supports multiple downloads however it is not used and only one resource is sent for downloading at a time.
I think we can increase / assure parallelism (even for single container requesting resource) for private/application resources by making multiple downloads per ContainerLocalizer.
Total Parallelism before
= number of threads allotted for PublicLocalizer [public resource] + number of containers[private and application resource]
Total Parallelism after
= number of threads allotted for PublicLocalizer [public resource] + number of containers * max downloads per container [private and application resource]