Comment 4 for bug 1876822

ok, so this is definitely exactly the situation described in https://www.remlab.net/op/futex-condvar.shtml
"If more than one thread goes to sleep in a row, the second one must not change the futex value. Otherwise, the first thread would potentially fail to go to sleep due to the changed futex value. The more threads wait on the same condition variable, the more likely the problem. With enough threads, it could degrade into a live loop."