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Standard condition variables have the following guarantees:
* if there are any waiters then signal()/notify() will awaken at least one of them;
* if there are any waiters then broadcast()/notify_all() will awaken all of them.
The implementation in condvar.h does not have these guarantees since a future waiter (possibly the signalling thread) may steal the signal intended for a current waiter.
In many cases this does not matter, but in some it can cause a deadlock. For instance, consider
 from threading import Condition, Thread
 import time
 def set_to_value(value, cond, state):
 while 1:
 with cond:
 while state.value == value:
 cond.wait()
 state.value = value
 print("set_to_value(%s)" % value)
 cond.notify_all()
 class state:
 value = False
 c = Condition()
 for i in (0, 1):
 t = Thread(target=set_to_value, args=(i, c, state))
 t.daemon = True
 t.start()
 time.sleep(5)
This *should* make state.value bounce back and forth between 0 and 1 continually for five seconds.
But using a condition variable implemented like in condvar.h this program is liable to deadlock because the signalling thread steals the signal intended for the other thread.
I think a note about this should be added to condvar.h.