PyNUT and blocking calls #3094
Description
I use PyNUT module to easily connect to and get data from a set of UPSes. I've discovered that some of module's calls (I'm using only CheckUPSAvailable and GetUPSVars; not tested with other ones) are blocking. When remote UPS is lost (it's primary controller rebooted or so) calling such methods will lead to the deadlock. As for now I've mitigated the problem by using signal module:
...
import signal
...
def timeout_handler(signal, frame):
raise Exception("timeout while querying UPS")
...
# check for UPS availability (with timeout)
signal.signal(signal.SIGALRM, timeout_handler)
signal.alarm(WAIT_TIME)
try:
if not upsc.CheckUPSAvailable(nut_name):
print("UPS is not available")
return False
except Exception as e:
print(f"Something wrong while checking UPS availability: {e}")
signal.alarm(0)
return False
signal.alarm(0)
return True
...
# get variables from UPS (with timeout)
signal.signal(signal.SIGALRM, timeout_handler)
signal.alarm(WAIT_TIME)
try:
curr_raw = upsc.GetUPSVars(nut_name)
except Exception as e:
print(f"Something wrong while getting variables from UPS: {e}")
signal.alarm(0)
return False
signal.alarm(0)
return True
I wonder whether there are more efficient ways to handle lockups. Or, may be, even plans to implement configurable timeouts in PyNUT...