I need to wait in a script until a certain number of conditions become true?
I know I can roll my own eventing using condition variables and friends, but I don’t want to go through all the trouble of implementing it, since some object property changes come from external thread in a wrapped C++ library (Boost.Python), so I can’t just hijack
__setattr__ in a class and put a condition variable there, which leaves me with either trying to create and signal a Python condition variable from C++, or wrap a native one and wait on it in Python, both of which sound fiddly, needlessly complicated and boring.
Is there an easier way to do it, barring continuous polling of the condition?
Ideally it would be along the lines of
res = wait_until(lambda: some_predicate, timeout) if (not res): print 'timed out'
Unfortunately the only possibility to meet your constraints is to periodically poll, e.g….:
import time def wait_until(somepredicate, timeout, period=0.25, *args, **kwargs): mustend = time.time() + timeout while time.time() < mustend: if somepredicate(*args, **kwargs): return True time.sleep(period) return False
or the like. This can be optimized in several ways if
somepredicate can be decomposed (e.g. if it’s known to be an
and of several clauses, especially if some of the clauses are in turn subject to optimization by being detectable via
threading.Events or whatever, etc, etc), but in the general terms you ask for, this inefficient approach is the only way out.