trigger at TDM/2 only


C

cerr

Hi,

I have a process that I can trigger only at a certain time. Assume I have aTDM period of 10min, that means, I can only fire my trigger at the 5th minute of every 10min cycle i.e. at XX:05, XX:15, XX:25... For hat I came up with following algorithm which oly leaves the waiting while loop if minute %TDM/2 is 0 but not if minute % TDM is 0:
min = datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime..now().timetuple().tm_min
while not (min%tdm_timeslot != 0 ^ min%(int(tdm_timeslot/2)) != 0):
time.sleep(10)
logger.debug("WAIT "+str(datetime.datetime.now().timetuple().tm_hour*60 +datetime.datetime.now().timetuple().tm_min))
logger.debug(str(min%(int(tdm_timeslot/2)))+" - "+str(min%tdm_timeslot))
min = datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime.now().timetuple().tm_min
logger.debug("RUN UPDATE CHECK...")

But weird enough, the output I get is something like this:
I would expect my while to exit the loop as soon as the minute turns 1435.... why is it staying in? What am I doing wrong here?

WAIT 1434
3 - 3
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1435
4 - 4
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1436
0 - 5
RUN UPDATE CHECK...


Thank you for any assistance!
Ron
 
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D

Dave Angel

Hi,

I have a process that I can trigger only at a certain time. Assume I have a TDM period of 10min, that means, I can only fire my trigger at the 5th minute of every 10min cycle i.e. at XX:05, XX:15, XX:25... For hat I came up with following algorithm which oly leaves the waiting while loop if minute % TDM/2 is 0 but not if minute % TDM is 0:
min = datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime.now().timetuple().tm_min
while not (min%tdm_timeslot != 0 ^ min%(int(tdm_timeslot/2)) != 0):

You might have spent three minutes and simplified this for us. And in
the process discovered the problem.

(BTW, min() is a builtin function, so it's not really a good idea to be
shadowing it.)

You didn't give python version, so my sample is assuming Python 2.7
For your code it shouldn't matter.

tdm = 10
tdm2 = 5

y = min(3,4)
print y

for now in range(10,32):
print now, now%tdm, now%tdm2,
print not(now % tdm !=0 ^ now%tdm2 !=0) #bad
print not((now % tdm !=0) ^ (now%tdm2 !=0)) #good


Your problem is one of operator precedence. Notice that ^ has a higher
precedence than != operator, so you need the parentheses I added in the
following line.

What I don't understand is why you used this convoluted approach. Why not

print now%tdm != tdm2

For precedence rules, see:
http://docs.python.org/2/reference/expressions.html#operator-precedence
 
M

MRAB

Hi,

I have a process that I can trigger only at a certain time. Assume I have a TDM period of 10min, that means, I can only fire my trigger at the 5th minute of every 10min cycle i.e. at XX:05, XX:15, XX:25... For hat I came up with following algorithm which oly leaves the waiting while loop if minute % TDM/2 is 0 but not if minute % TDM is 0:
min = datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime.now().timetuple().tm_min
while not (min%tdm_timeslot != 0 ^ min%(int(tdm_timeslot/2)) != 0):
time.sleep(10)
logger.debug("WAIT "+str(datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime.now().timetuple().tm_min))
logger.debug(str(min%(int(tdm_timeslot/2)))+" - "+str(min%tdm_timeslot))
min = datetime.datetime.now().timetuple().tm_hour*60 + datetime.datetime.now().timetuple().tm_min
logger.debug("RUN UPDATE CHECK...")

But weird enough, the output I get is something like this:
I would expect my while to exit the loop as soon as the minute turns 1435... why is it staying in? What am I doing wrong here?

WAIT 1434
3 - 3
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1434
4 - 4
WAIT 1435
4 - 4
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1435
0 - 5
WAIT 1436
0 - 5
RUN UPDATE CHECK...
Possibly it's due to operator precedence. The bitwise operators &, |
and ^ have a higher precedence than comparisons such as !=.

A better condition might be:

min % tdm_timeslot != tdm_timeslot // 2

or, better yet, work out how long before the next trigger time and then
sleep until then.
 
C

cerr

DaveA,

Yep, that seems to just be about it! Much easier!

Thanks for the hint! Much appreciated!!!! :)

Ron
 
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