Kivy crashes after setting system clock back in time

[Bounder]

I'm currently developing an app on OSX (Version 10.11.3) which displays a analog clock, so i'm testing how the clock updates when the system time is adjusted for summer/winter time. I found out when adjusting the system time by adding an hour fire's all events, which is inconvenient but not a problem for me. However setting the system time back with one hour crashes Kivy. I also tested this in an unrelated Kivy app which also crashed, so I think this problem is universal for Kivy on OSX.

I did not had the time yet to determine if this problem exists an all platforms or just OSX. It would be nice to know if this is the case. Attached to this issue you'll find the stack trace I get when aborting the debug session.

 Traceback (most recent call last):
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/app.py", line 824, in run
     runTouchApp()
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/base.py", line 487, in runTouchApp
     EventLoop.window.mainloop()
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/core/window/window_sdl2.py", line 539, in mainloop
     self._mainloop()
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/core/window/window_sdl2.py", line 300, in _mainloop
     EventLoop.idle()
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/base.py", line 327, in idle
     Clock.tick()
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/clock.py", line 461, in tick
     usleep(1000000 * (sleeptime - sleep_undershoot))
   File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/clock.py", line 267, in usleep
     _default_sleep(microseconds / 1000000.)
 KeyboardInterrupt

[dessant]

Thanks for the report. There was a pr which fixes this in some cases: #2906.

It didn't always work, and produced this exception (#3797):

I/python (14014): File "...main.py", line 18, in
I/python (14014): File ".../kivy/app.py", line 319, in
I/python (14014): File ".../kivy/base.py", line 29, in
I/python (14014): File ".../kivy/clock.py", line 278, in
I/python (14014): File ".../kivy/clock.py", line 258, in libc_clock_gettime_wrapper
I/python (14014): File ".../python2.7/ctypes/__init_.py", line 369, in getattr
I/python (14014): File ".../ctypes/init.py", line 374, in getitem
I/python (14014): AttributeError: undefined symbol: clock_gettime

Currently we fall back to the old implementation when there is an exception:
cf31ef7

@matham pointed out this solution, it would be cross-platform, but it only applies to python 3:
https://www.python.org/dev/peps/pep-0418/#time-monotonic

[Bounder]

Thanks for the quick answer. I updated my Kivy environment to version 1.9.1-dev0 / Python 2.7.10 and I found out Kivy still hangs. After debugging I saw it went directly to the fallback implementation. After some googling found out that OS X El Capitan moved the libc library, they can now be accessed using the following path:/usr/lib/libc.dylib instead of libc.dylib , however after changing the path Kivy still hangs on:

File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/app.py", line 828, in run runTouchApp() File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/base.py", line 487, in runTouchApp EventLoop.window.mainloop() File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/core/window/window_sdl2.py", line 619, in mainloop self._mainloop() File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/core/window/window_sdl2.py", line 362, in _mainloop EventLoop.idle() File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/base.py", line 327, in idle Clock.tick() File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/clock.py", line 493, in tick usleep(1000000 * (sleeptime - sleep_undershoot)) File "/Applications/Kivy.app/Contents/Resources/kivy/kivy/clock.py", line 285, in usleep _libc_usleep(int(microseconds))

I will check later today if everything works on ubuntu 14.04.
[edit: Just checked, On Ubuntu everything works fine, when using 1.9.1]

[dessant]

Here is a cross-platform solution: https://pypi.python.org/pypi/monotonic.

[KeyWeeUsr]

@dessant Wouldn't it be better to include monotonic into kivy? Roboto font has Apache 2.0 license too, so licensing probably shouldn't be a problem. If the speed is the factor, maybe including Monoclock might be the answer(as it's MIT), but that needs a work done for windows and maybe iOS?

[dessant]

I'd ask @matham which path seems best.

[Julian-O]

I note that monotonic is built into Python >3.3, so we can just use that now.

[misl6]

Some additional info for the future:

In Python 3.11, time.sleep:

Changed in version 3.11: On Unix, the clock_nanosleep() and nanosleep() functions are now used if available. On Windows, a waitable timer is now used.

Basically, now Python almost follows our approach, but by using a monotonic clock.

Idea 💡: Better to use time.sleep() instead of our custom solution for 3.11 and onwards?