race condition on lock :(

[FxIII]

I think there is a race condition on
luigi/lock.py", line 93, in acquire_for

# Check if there is a pid file corresponding to this name
if not os.path.exists(pid_dir):
  os.mkdir(pid_dir)

between if not [...] and mkdir another process could have created the pid_dir resulting in an unhandled OSError exception.

I think that ignore the exception if the folder exists will be enough, or perhaps just create the folder and say sorry if it was just there...

[dlstadther]

Feel free to submit a Pull Request if you believe os.mkdir should be surrounded in try/except (or whatever solution you believe to be best)!

Thanks