Does PeriodicCallback ensure no parallel executions? Is the callback triggered while a previous triggered one is still running or does it ensure that there is only one callback running at a time? As far as I can see the later one is true, but I want to be sure! I should control that time of asynchronous function is no longer than next periodiccallback scheduler.
For example:
If I have a periodiccallback every 5 seconds and my function time sometimes (because makes http request etc) is longer (for example 7 second), how can I jump the "10 second" and pass to 15? Only when it happens.
The tornado docs says
If the callback runs for longer than callback_time milliseconds, subsequent invocations will be skipped to get back on schedule.
So if I'm understanding your question correctly, PeriodicCallback already does exactly what you want if your callback is a synchronous function!
If your callback isn't synchronous, then you will need to use locks to check yourself if something is already running or not. Something like:
from tornado import gen, locks
lock = locks.Lock()
running = False
@gen.coroutine
def task():
global running
with (yield lock.acquire()):
if running:
return
running = True
try:
yield do_something()
finally:
with (yield lock.acquire()):
running = False
http://www.tornadoweb.org/en/stable/ioloop.html#tornado.ioloop.PeriodicCallback