// purely for debugging.
func gcMarkRootCheck() {
	if work.markrootNext < work.markrootJobs {
		print(work.markrootNext, " of ", work.markrootJobs, " markroot jobs done\n")
		throw("left over markroot jobs")
	}

	// Check that stacks have been scanned.
	//
	// We only check the first nStackRoots Gs that we should have scanned.
	// Since we don't care about newer Gs (see comment in

	// close.
	//
	// Put this field here because it needs 64-bit atomic access
	// (and thus 8-byte alignment even on 32-bit architectures).
	bytesMarked uint64

	markrootNext uint32 // next markroot job
	markrootJobs uint32 // number of markroot jobs

	nproc  uint32
	tstart int64
	nwait  uint32

	// Number of roots of various root types. Set by gcMarkRootPrepare.
	//