6966222: G1: simplify TaskQueue overflow handling Reviewed-by: tonyp, ysr

6930581: G1: assert(ParallelGCThreads > 1 || n_yielded() == _hrrs->occupied(),"Should have yielded all the .. Summary: During RSet updating, when ParallelGCThreads is zero, references that point into the collection set are added directly the referenced region's RSet. This can cause the sparse table in the RSet to expand. RSet scanning and the "occupied" routine will then operate on different instances of the sparse table causing the assert to trip. This may also cause some cards added post expansion to be missed during RSet scanning. When ParallelGCThreads is non-zero such references are recorded on the "references to be scanned" queue and the card containing the reference is recorded in a dirty card queue for use in the event of an evacuation failure. Employ the parallel code in the serial case to avoid expanding the RSets of regions in the collection set. Reviewed-by: iveresov, ysr, tonyp

6963209: G1: remove the concept of abandoned pauses Summary: As part of 6944166 we disabled the concept of abandoned pauses (i.e., if the collection set is empty, we would still try to do a pause even if it is to update the RSets and scan the roots). This changeset removes the code and structures associated with abandoned pauses. Reviewed-by: iveresov, johnc