This time, the issue was that we could race a wait and a wake. A multi-
token waiter would not notice that the number of tokens changed because
it only performed a fetch-and-OR, then waited on the high part which did
not change. That means the futex_wait() would succeed, when we wanted it
to have failed.
So we have to bring back a portion of what commit
081c001deb removed: we need to keep both
the token count and the waiter count in the high word.
Task-number: QTBUG-67214
Change-Id: I04a43ee94975482f9e32fffd151e467a9e0030b3
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
72f8f994b2