During the code review cycle for JDK-8199813, Erik O
came up with a way to verify the contract for thread_do()
which is currently only in comment form:

// All JavaThreads + all non-JavaThreads (i.e., every thread in the system)
void Threads::threads_do(ThreadClosure* tc) {

This new function will be called:

ThreadsSMRSupport::verify_hazard_pointer_scanned()

and will require some support infrastructure changes
to implement it.