License

This code is licensed under the MIT license This code is based on a implementation by Nick Garvish, found on http://nick.vargish.org/clues/python-tricks.html

Simple Signal Watchdog

Provides a simple UNIX-signal based watchdog. It may be used either as a context manager or as a decorator. The default behaviour is to raise a Timeout exception when the given number of seconds has passed.

Usage

Decorator usage

>>> @watchdog(3)
>>> def nii(delay):
...   time.sleep(delay);
...

>>> nii(2);          # will pass successfully
>>> nii(3);          # will pass successfully
>>> nii(4);
[...]
watchdog.Timeout: Execution timed out (limit was 3 seconds)

Context Manager usage

>>> with watchdog(5):
...   time.sleep(10);
watchdog.Timeout: Execution timed out (limit was 5 seconds)

Remarks

Portability

This implementation is based on UNIX signals and, as such, should not work on non- unix platforms (e.g. Windows).

Advantages

This implementation is simpler than using threads. Also, unlike a thread-based implementation, it manages to raise an exception in the same context as the calling code.

Disavantadges

It is less capable than a thread-based watchdog implementation, in that its timeout granularity is seconds.

Also, some people reported that it may not work under certain unknown conditions. I have not seen it happen so far. This is discussed by Gavin Andressen in detail on http://gavintech.blogspot.com/2008/02/python-sigalrm-oddness.html (where another implementation (fork-based) implementation is suggested).