Listing 9.12: a question about locking

[alexsimonov999]

The line 61 is commented out in the repository (compared to the printed book):
// self->set_clear_mutex.unlock();
Why?
And it is suspicious that the order of set_clear_mutex and lk locking changes: initially lk is locked first (it must be locked before the call to interruptible_wait) and set_clear_mutex is locked second (in the ctor of custom_lock); but then the order changes in custom_lock::lock().
Is it really correct?

[alexsimonov999]

And one more thing about the listing 9.12. In paragraph following the listing we read: "You can now check for an interruption without worrying about races. If the interrupt flag is set at this point, it was set before you acquired the lock on set_clear_mutex." But set_clear_mutex protects only access to thread_cond and a call to notify_all, not setting a flag. Maybe I'm wrong but as I understand, the flag can be set in some thread using set() function even if another thread has already locked set_clear_mutex.