Summary: Under certain circumstances a safepoint could happen between a JavaThread object being created and that object being added to the Java threads list. This could cause the active field of that thread's SATB queue to get out-of-sync with respect to the other Java threads. The solution is to activate the SATB queue, when necessary, before adding the thread to the Java threads list, not when the JavaThread object is created. The changeset also includes a small fix to rename the surrogate locker thread from "Surrogate Locker Thread (CMS)" to "Surrogate Locker Thread (Concurrent GC)" since it's also used in G1.
Reviewed-by: iveresov, ysr, johnc, jcoomes

Summary: Clear the concurrent marking "in progress" flag while the FullGCCount_lock is held. This avoids a race that can cause back to back System.gc() calls, when ExplicitGCInvokesConcurrent is enabled, to fail to initiate a marking cycle causing the requesting thread to hang.
Reviewed-by: tonyp, ysr

Summary: Concurrent collectors should expand the perm gen without a full STW GC, but possibly by triggering a concurrent collection. Temporary band-aid for G1 where no concurrent collection is kicked off since the perm gen is not collected concurrently.
Reviewed-by: johnc

Reviewed-by: ysr

6692906: CMS: parallel concurrent marking may be prone to hanging or stalling mutators for periods of time
Summary: Inserted missing yield(check)s in closures used during the work-stealing phase of parallel concurrent marking, a missing synchronous yield-request in the cms perm gen allocation path, and a terminator-terminator for the offer_termination invocation that monitors the yield status of the concurrent marking task. Elaborated some documentation comments and made some task queue termination loop flags configurable at start-up to aid debugging in the field.
Reviewed-by: jmasa, johnc, poonam

6942771: SEGV in ParScanThreadState::take_from_overflow_stack
Reviewed-by: apetrusenko, ysr, pbk

Summary: Re-enable use of the lock-free versions of region stack push() and pop() by recording aborted regions in a thread-local structure, which are then processed when scanning of the region stack restarts. The previous locking versions of these routines are retained for diagnostic purposes.
Reviewed-by: tonyp, ysr

Reviewed-by: ohair

Summary: Associate number of GC workers with the workgang as opposed to the task.
Reviewed-by: johnc, ysr

Reviewed-by: ohair, kvn

Summary: Pass correct value for length to NumberSeq constructor. Guard dereferences of "body_summary" pointer with a NULL check.
Reviewed-by: tonyp, ysr

Summary: Emit a fake frame that makes it look like the thread is in the OutOfMemoryError zero-parameter constructor
Reviewed-by: dcubed

Summary: Fixed comment/documentation typos; converted some guarantee()s to assert()s.
Reviewed-by: jmasa

Summary: Update the Major and Build numbers for HS20
Reviewed-by: jcoomes

Summary: Use javac's @filename construct to avoid long compile lines
Reviewed-by: ohair, twisti, never
Contributed-by: doko@ubuntu.com

Summary: See synopsis
Reviewed-by: ohair

Summary: Must check locals for null when processing chop frame
Reviewed-by: dholmes, dcubed