In my ANYLOGIC model there are certain services( some delays the agent from 10 to 15 minutes, others 4 to 8 hrs), using certain resources from a resource pool.
The resources (pool) are available as per a well defined time ( Available: entire week except sunday , 10 am to 1:30 pm and then 2:00 Pm to 6 pm.).
I can see that once a service starts it continues till it finishes itself even after the resource availability time is over.
For example:
A resource is available :entire week except sunday , 10 am to 1:30 pm and then 2:00 Pm to 6 pm.
A service( of 8 hrs delay) starts from 12:30 pm....once it starts, it gets continue till it get finished. Practically it shall release resource from 1:30 to 2 pm and also if the task is not over then it shall not continue beyond 6 pm as well, and shall stop the same and start next day(or next availability).
but it does continue once it starts till it gets finished.
kindly suggest the specific area to be targeted to code or any other option is available?
Define your resource-pool downtimes using a Downtime block. Tick it's "may preempt other tasks" as below:
NOTE: play around with preemption as it interacts with Seize-preemption, resource pool preemption and priorities. Start simple and add complexity only when you fully understand how things work under the hood
I am trying to make a cron-job that runs a function after 24 hours but if it's a friday, then the timer should stop at 23:59 and restart on sunday at 23:59. How do I do this?
Imagine a request being created. When this is created, an email function has to be called. If a reply for the said email is not received within 24 hrs, the email function should be called again and the 24 hrs timer should start again to repeat this process for a third time. But if it is a saturday and the timer is running, it should stop and then restart back on monday. (This is to indicate that no time from saturday or sunday has been consumed in the timer).
Some cron patterns allow you to specify day ranges (e.g. 59 23 * * 1-5 runs only Monday to Friday).
Fore more complicated logic, setting the cron to run everyday + inspecting the day of the week in your application might be simpler like O. Jones commented.
Personally, I'd lean towards the latter so you can log when the cron ran and skipped because it was a weekend, so you have a record, if things ever go wrong or you need to debug something.
First Example
Suppose I have a CRON job
30 2 * * * ....
Then this would run every time when it is 2:30 at night (local time).
Now suppose I have the time zone Europe/Germany and it's 2017-10-29 (the day when DST is switched). Then this CRON job would run twice, right?
Second Example
Suppose I have the time zone Europe/Germany and the CRON job
30 11 * * * ....
As Germany never had a DST change at 11:30, this will not interfere. But the user could change the local time. To be super clear: This question is NOT about DST.
For the following test cases, I would like to know if/how often the CRON job gets scheduled:
At 11:29:58.0, the user sets the time to 11:31:00
At 11:29:59.1, the user sets the time to 11:31:00
At 11:29:59.6, the user sets the time to 11:31:00
At 11:30:01.0, the user sets the time to 11:29:59.7 - is CRON executed directly afterwards?
They boil down to How quickly is CRON triggered?, where the 4th one also has the question if CRON stores that it was already executed for that minute.
Another variant of the same question:
At 11:29:59, the NTP service corrects the time to 11:31:00 - will the job be executed that day at all?
The easiest way to answer this with confidence is to take a look at the source for the cron daemon. There are a few versions online like this, or you can use apt-get source cron.
The tick cycle in cron is to repeatedly sleep for a minute, or less if there is a job coming up. Immediately after emerging from the sleep, it checks the time and treats the result as one of these wakeupKind values:
Expected time - run any jobs we were expecting
Small jump forwards (up to 5 minutes) - run the jobs for the intervening minutes
Medium jump forwards (up to 3 hours, so this would include DST starting in spring) - run any wildcard jobs first (because the catch up could take more than a minute), then catch up on the intervening fixed time jobs
Large jump (3 hours or more either way) - start over with the current time
Jump backwards (up to 3 hours, so including the end of DST) - because any fixed time jobs have 'probably' already run, only run any wildcard jobs until the time is caught up again
If in doubt, the source comments these wakeupKind values clearly.
Edit
To follow up on whether sleep() could be affected by a clock change, it looks like the answer is indirectly there in a couple of the Linux man pages.
Firstly the notes for the sleep() function confirm that is implemented by nanosleep()
The notes for nanosleep() say Linux measures the time using the CLOCK_MONOTONIC clock (even though POSIX.1 says it shouldn't)
Scroll down a bit in the docs for clock_settime() to see the explanation of CLOCK_MONOTONIC, which explains it is not affected by jumps in the system time, but it would be affected by incremental NTP style clock sync adjustments.
So in summary, a system admin style clock change will have no effect on the sleep(). But for example if an NTP adjustment came in and said to 'gently' advance the clock, cron would experience a series of slightly short sleep() function calls.
There are many implementations of cron systems (See here). One of the most commonly used cron's is Vixie cron. And its man page states:
Daylight Saving Time and other time changes
Local time changes of less than three hours, such as those caused by the Daylight Saving Time changes, are handled in a special way. This only applies to jobs that run at a specific time and jobs that run with a granularity
greater than one hour. Jobs that run more frequently are scheduled normally.
If time was adjusted one hour forward, those jobs that would have run in the interval that has been skipped will be run immediately. Conversely, if time was adjusted backwards, running the same job twice is avoided.
Time changes of more than 3 hours are considered to be corrections to the clock or the timezone, and the new time is used immediately.
source: man 8 cron
I believe this answers most of your points.
In addition to point five:
At 11:29:59, the NTP service corrects the time to 11:31:00 - will the job be executed that day at all?
First of, if NTP corrects the time with more then a minute, you have a very bad clock! This should not happen too often. Generally, you might have such a step when you enable NTP but then it should be much less.
In any case, if the DeltaT is not to high, generally below 125 ms, your system will slew the time. Slewing the time means to change the virtual frequency of the software clock to make the clock go faster or slower until the requested correction is achieved. Slewing the clock for a larger amount of time may require some time, too. For example standard Linux adjusts the time with a rate of 0.5ms per second.
This implies, (under the assumption of Vixie cron, and probably many others):
If NTP jumps more then 3 hours, the job is skipped
If NTP jumps less then 3 hours but more then 125 ms, Vixie cron handles the job nicely by assuming the concepts of the time-jumps.
If NTP corrects the time for less then 125 ms, cron does not notice the time-jump due to the slewing.
Interesting information:
RFC5905: Network Time Protocol Version 4: Protocol and Algorithms Specification
The NTP FAQ and Howto
https://wiki.gentoo.org/wiki/Cron/en
You're actually asking two related questions. The general answer is it depends[1], but I'll answer based on the Debian Linux installation I'm on right now:
How does cron handle DST changes and other 'special' time-related events?
On my Debian Linux system cron handles 'DST and other time-related changes/fixes' (per the man page) so that jobs don't get run twice or skipped due to changes like DST. (See https://debian-handbook.info/browse/stable/sect.task-scheduling-cron-atd.html for more specifics) Related to the 5th point raised in your second question, I would expect these same facilities to deal with NTP-related time jumps but don't know for certain.
How often is cron triggered and how quickly does it pick up my crontab changes?
Again, on my Debian Linux system the cron daemon wakes up once a minute and will detect and utilize any crontab changes man since the previous check/run one minute ago. Note that there is no guarantee that cron fires off at 12:00:00 or 12:00:59 or any specific time between (only that it fire when the time is 12:00:??) so in the event that you change a crontab at 12:00:17 but cron fired at 12:00:13, your changes will not be picked up until the next run (most likely at 12:01:13 though there might be a slight amount of variance due to the Linux scheduler)
[1] It Depends...
The precise answer absolutely depends both on the platform (Linux/Unix/BSD/OS X/Windows) and the particular implementation of cron (there have been several over the decades with derivatives of Vixie cron being prevalent on Linux and BSD per https://en.wikipedia.org/wiki/Vixie_cron). If you're running something other than Linux, the man page / documentation for your implementation should provide details as to the specifics of how often it runs, picks up modified crontabs, DST handling etc. If you really need to know the specific details, df778899 is right in that you should look at the source code for your implementation as needed... because sometimes software/documentation is buggy.
On mac OS:
$> man cron
...
Available options:
-s Enable special handling of situations when the GMT offset of the local timezone changes, such as the switches between the standard time and daylight saving time.
The jobs run during the GMT offset changes time as intuitively expected. If a job falls into a time interval that disappears (for example, during the switch from standard time) to daylight saving time
or is duplicated (for example, during the reverse switch), then it is handled in one of two ways:
The first case is for the jobs that run every at hour of a time interval overlapping with the disappearing or duplicated interval. In other words, if the job had run within one hour before the GMT
offset change (and cron was not restarted nor the crontab(5) changed after that) or would run after the change at the next hour. They work as always, skip the skipped time or run in the added time as
usual.
The second case is for the jobs that run less frequently. They are executed exactly once, they are not skipped nor executed twice (unless cron is restarted or the user's crontab(5) is changed during
such a time interval). If an interval disappears due to the GMT offset change, such jobs are executed at the same absolute point of time as they would be in the old time zone. For example, if exactly
one hour disappears, this point would be during the next hour at the first minute that is specified for them in crontab(5).
-o Disable the special handling of situations when the GMT offset of the local timezone changes, to be compatible with the old (default) behavior. If both options -o and -s are specified, the option
specified last wins.
I've been looking for this for a while now, but I didn't find a way to do what I want.
I have a Web Page in which a user can plan some actions during a week.
For example:
On monday morning, from 8:00 to 10:00, do this...
On tuesday afternoon, from 1:30 to 2:00, do that...
Well, I would like that my Java program automatically launch the actions for the periods that the user selected. And, during these time intervals, repeat the action every X minutes. (Should be configurable)
What I thought was setting up Quartz with Cron scheduler. However, I don't know how to handle half hours...
More precisely:
This will work for my first example (repeat every 5 minutes between 8 to 10):
0 0/5 8-10 * * MON
But how to handle the second example? (Starting at 1:30 but repeat the action every 5 minutes??)
Thanks !
Philippe
actually I found an answer to my needs: DailyTimeIntervalScheduleBuilder !
Here is an example for answer my need:
DailyTimeIntervalScheduleBuilder scheduleBuilder = DailyTimeIntervalScheduleBuilder.dailyTimeIntervalSchedule()
.startingDailyAt(new TimeOfDay(13, 30, 0))
.endingDailyAt(new TimeOfDay(14, 0, 0))
.onDaysOfTheWeek(1)
.withIntervalInMinutes(5);
Problem solved
Philippe
(I apologize in advance for bad formulation of my problem, please consider english is not my first language).
I have several processes (crons) and I want to "optimize" the schedule when to launch them.
For example, cron c1 starts every 3 minutes, cron c1 starts every 7 minutes and cron c3 starts every 18 minutes. Assume they last only a few seconds before stopping.
The unit of time here is 1 minute.
Now, what I want is that these crons are distributed so that we don't have a moment where many of them start and then long time interval with no cron at all. For example, if c1 and c3 both start at time 0, then they will start again together every 18 minutes. It would be better to start cron c1 at time 0 and then c3 at time 1, so that they are never launched together.
So the idea is, given a list of crons with periodicity, to plan a schedule, so that there is as much time between each cron as possible and as few as possible moments when two crons start together.
Are there some well-known algorithms about such problems?
The real-life application of this problem is: ~ 200 crons. Some of them are launched every 5 or ~10 or ~30 minutes and last very short (few seconds), some (~20 - 25) are launched every 2 hours and last a few minutes. So the idea is also that the big crons are not launched at the same time.
I am a mathematician myself and not a computer scientist, so I asked this question on https://math.stackexchange.com/, since I consider this being a "nice" question for mathematicians too.
I think you should consider the ressources used by each of your crons and then schedule your jobs from that.
I don't think there is a particular algorithm for that.