def METHOD_NAME(self):
    #do every callback on a separate thread
    n = 32 #total callbacks
    threads = []
    class foo(object):pass
    context = foo()
    context.l = []
    context.n = 2 #submits per thread
    context.nThreads = n // context.n
    context.nFinished = 0
    context.lock = threading.Lock()
    context.event = threading.Event()
    for i in range(context.nThreads):
        t = threading.Thread(target=self.pendingcalls_thread, args = (context,))
        t.start()
        threads.append(t)
    self.pendingcalls_wait(context.l, n, context)
    for t in threads:
        t.join()