What are the phases of the concurrent low pause collector?
There are six phases involved in the collection: Phase 1 (Initial Checkpoint) involves stopping all the Java threads, marking all the objects directly reachable from the roots, and restarting the Java threads. Phase 2 (Concurrent Marking) starts scanning from marked objects and transitively marks all objects reachable from the roots. The mutators are executing during the concurrent phases 2, 3, and 5 below and any objects allocated in the CMS generation during these phases (including promoted objects) are immediately marked as live. Phase 3: During the concurrent marking phase mutators may be modifying objects. Any object that has been modified since the start of the concurrent marking phase (and which was not subsequently scanned during that phase) must be rescanned. Phase 3 (Concurrent Precleaning) scans objects that have been modified concurrently. Due to continuing mutator activity the scanning for modified cards may be done multiple times. Phase 4 (Final Checkpoint) is a stop-the-
