6909756: G1: guarantee(G1CollectedHeap::heap()->mark_in_progress(),"Precondition.") Summary: Make sure that two marking cycles do not overlap, i.e., a new one can only start after the concurrent marking thread finishes all its work. In the fix I piggy-back a couple of minor extra fixes: some general code reformatting for consistency (only around the code I modified), the removal of a field (G1CollectorPolicy::_should_initiate_conc_mark) which doesn't seem to be used at all (it's only set but never read), as well as moving the "is GC locker active" test earlier into the G1 pause / Full GC and using a more appropriate method for it. Reviewed-by: johnc, jmasa, jcoomes, ysr

os_family = linux

arch = x86

arch_model = x86_64

os_arch = linux_x86

os_arch_model = linux_x86_64

lib_arch = amd64

compiler = sparcWorks

gnu_dis_arch = amd64

sysdefs = -DLINUX -DSPARC_WORKS -D_GNU_SOURCE -DAMD64