hacky decorators for defeating annoying race conditions

do_when.py

""" some decorator hacks for defeating annoying race conditions """

def when(predicate, limit=100, sleep_time=1, eager=False):
    """ this function is dedicated to Christopher Michael Heisel

        When predicate is True, the decorated function will run
        (and nevermind exactly when it was called).  If the predicate
        tests False for more times than <limit>, this function will
        simply exit and the decorated function will never be called.

        NOTE: you still need to call your function, unless eager=True

        Example usage:

           @when(lambda: AppCache().app_cache_ready())
           def do_patch():
               trivialize_method('ellington.alerts.tests.lists',
                                 'AlertListsTestCase',
                                 'test_admin_2_subs')
           do_patch()

    """
    def wrapper(func):
        def inner(*args, **kargs):
            def real_one():
                count = 0
                while True:
                    count+=1
                    time.sleep(sleep_time)
                    if predicate(): break
                    if count>limit: break
                if count<limit:
                    func(*args, **kargs)
            threading.Thread(target=real_one).start()
        if eager: inner()
        return inner
    return wrapper

def do_when(predicate, **kargs):
    """ shortcut: like when(), except always eager """
    return when(predicate,eager=True,**kargs)

def do_when_appcache_ready(**kargs):
    """ shortcut: like do_when, except predicate is implied """
    predicate = lambda: AppCache().app_cache_ready()
    return do_when(predicate,**kargs)