unique_lock::unlock() does not protect modification of is_locked with mutex

[Andrei Kazarov <Andrei.Kazarov@…>]

Shouldn't first is_locked=false and then m->unlock()? Otherwise is_locked value is undetermined in case of simultaneous calls to lock() and unlock()...

void unlock() { ... m->unlock(); is_locked=false; }

void lock() { ... m->lock(); is_locked=true; }

[Steven Watanabe]

A unique_lock is not intended to be accessed concurrently from multiple threads.