Concurrency utilities, in most part adapted or taken literally from dl.util.concurrent library by Doug Lea and partially modified to match the incoming JDK 1.5 java.util.concurrent package. This package contains a subset of java.util.concurrent functionality; however, it adds several extensions, mostly security related: The most prominent use of these extensions is in the middleware systems, where it is not uncommon for separate executable actions to run with different access permissions, depending on the identity of a subject that requested them.