In the Windows version of SemaphoreTicketHolder::_tryAcquire, if _numTickets is less than 0 we print an ominous-sounding message "DISASTER! in TicketHolder" to std::cerr. However, since resizing the ticket holder simply adjusts _numTickets, it doesn't seem incorrect for _numTickets to be less than 0 if the ticket holder gets resized to a smaller size while the number of available tickets is low.