I'm looking at using Windows WF to implement a system, which includes the need to support workflows that have either transitions or activities that need to be scheduled to execute at either a certain date/time in the future, or after a certain period of time has elapsed.
I found a question along these lines already:
Windows Workflow Foundation - schedule activities to run at certain times
Which suggests using the Delay task and calculating the duration of the delay in order to proceed at the required time. I have a few additional questions however, but don't have enough reputation to add comments so I'm posting a secondary question:
How can I implement it such that it can recover from a crash? For example, let's say the task is currently in the delay task and the process hosting the workflow engine crashes. When it is restarted, will it resume waiting in the delay task, and trigger at the time required? Do you have to do something special to get this to happen?
Another question is, again let's say a workflow instance is already mid-way through the delay task. At that point, you suddenly need to alter the time/date at which the workflow progresses to the next activity/task. Is it possible to programmatically update the duration on the in-play delay task to effect this?
If you store started instances in the SQL Store, you can add Persist activity each time you want to force save it. After crash activity will continue from last persist.
You can replace single big Delay with While cycle. In condition you check if you need to delay or not, in body you place Delay activity with short interval. You can add persist after that short Delay and instance will not wait full time again after crash (it depends on While condition, you need to store somewhere state of your instances. For example in variable).
Related
In my turn based online game I have a timer in-game, that ticks down from 24 hours to 0, when it reaches 0 for any player they have lost.
When a player makes their turn they write something like this to the database:
action: "not important"
timeStamp: 1670000000
What I want is for either of the two players to be able to get into the ongoing game at any time, read "timeStamp" and set the clock accordingly, showing how much time is left since the last action.
When writing to the database I am using ServerValue.TIMESTAMP (Android). I am aware of the ability to estimate the server time using ServerTimeOffset described here;
https://firebase.google.com/docs/database/android/offline-capabilities#server-timestamps
But I feel it's not always accurate when testing, so I wanted to explore if there is any other way to do this. What I really want is to get the actual server timestamp when reading the node:
timeLeft = actionTimeStamp - currentServerTime + 24h
Is this possible to do in ONE call? I am using RTDB, but I am open to moving to Firestore if it is possible there somehow.
There's no way to get the server timestamp without writing it to the database, but you can of course have each client write it and then immediately read it back.
That said, it shouldn't make much of a difference from using the initial start time that was written and the serverTimeOffset value.
For a working example, have a look at How to implement a distributed countdown timer in Firebase
The problem
I have a firebase application in combination with Ionic. I want the user to create a group and define a time, when the group is about to be deleted automatically. My first idea was to create a setTimeout(), save it and override it whenever the user changes the time. But as I have read, setTimeout() is a bad solution when used for long durations (because of the firebase billing service). Later I have heard about Cron, but as far as I have seen, Cron only allows to call functions at a specific time, not relative to a given time (e.g. 1 hour from now). Ideally, the user can define any given time with a datetime picker.
My idea
So my idea is as following:
User defines the date via native datepicker and the hour via some spinner
The client writes the time into a seperate firebase-database with a reference of following form: /scheduledJobs/{date}/{hour}/{groupId}
Every hour, the Cron task will check all the groups at the given location and delete them
If a user plans to change the time, he will just delete the old value in scheduledJobs and create a new one
My question
What is the best way to schedule the automatic deletion of the group? I am not sure if my approach suits well, since querying for the date may create a very flat and long list in my database. Also, my approach is limited in a way, that only full hours can be taken as the time of deletion and not any given time. Additionally I will need two inputs (date + hour) from the user instead of just using a datetime (which also provides me the minutes).
I believe what you're looking for is node schedule. Basically, it allows you to run serverside cron jobs, it has the ability to take date-time objects and schedule the job at that time. Since I'm assuming you're running a server for this, this would allow you to schedule the deletion at whatever time you wish based on the user input.
An alternative to TheCog's answer (which relies on running a node server) is to use Cloud Functions for Firebase in combination with a third party server (e.g. cron-jobs.org) to schedule their execution. See this video for more or this blog post for an alternative trigger.
In either of these approaches I recommend keeping only upcoming triggers in your database. So delete the jobs after you've processed them. That way you know it won't grow forever, but rather will have some sort of fixed size. In fact, you can query it quite efficiently because you know that you only need to read jobs that are scheduled before the next trigger time.
If you're having problems implementing your approach, I recommend sharing the minimum code that reproduces where you're stuck as it will be easier to give concrete help that way.
The question
Is it possible (and if so, how) to make it so when an object's field x (that contains a timestamp) is created/updated a specific trigger will be called at the time specified in x (probably calling a serverless function)?
My Specific context
In my specific instance the object can be seen as a task. I want to make it so when the task is created a serverless function tries to complete the task and if it doesn't succeed it updates the record with the partial results and specifies in a field x when the next attempt should happen.
The attempts should not span at a fixed interval. For example, a task may require 10 successive attempts at approximately every 30 seconds, but then it may need to wait 8 hours.
There currently is no way to (re)trigger a Cloud Function on a node after a certain timespan.
The closest you can get is by regularly scheduling a cron job to run on the list of tasks. For more on that, see this sample in the function-samples repo, this blog post by Abe, and this video where Jen explains them.
I admit I never like using this cron-job approach, since you have to query the list to find the items to process. A while ago, I wrote a more efficient solution that runs a priority queue in a node process. My code was a bit messy, so I'm not quite ready to share it, but it wasn't a lot (<100 lines). So if the cron-trigger approach doesn't work for you, I recommend investigating that direction.
I have a box job that is dependent on another job finishing. The first job normally finishes by 11pm and my box job then kicks off and finishes in about 15 minutes. Occasionally, however, the job may not finish until much later. If it finishes later than 4am, I'd like to have it send an alert.
My admin told me that since it is dependent on a prior job, and not set to start at a specific time, it is not possible to set a time-based alert. Is this true? Does anybody have a workaround they can suggest? I'd rather not set the alert on the prior job (suggested by my admin) as that may not always catch those instances when my job runs longer.
Thanks!
You can set a max run alarm time which will alert if that time is exceeded
We ended up adding a job to the box with a start time of 4am that checks for the existence of the files the rest of the job creates. We also did this for the jobs predecessors to make sure we are notified if we are at risk of not finishing by 4am.
I am building a scheduling system. The current system is just using excel, and they type in times like 9:3-5 (meaning 9:30am-5pm). I haven't set up the format for how these times are going to be stored yet, I think I may have to use military time in order to be able to calculate the hours, but I would like to avoid that if possible. But basically I need to be able to figure out how to calculate the hours. for example 9:3-5 would be (7.5 hours). I am open to different ways of storing the times as well. I just need to be able to display it in an easy way for the user to understand and be able to calculate how many hours it is.
Any ideas?
Thanks!!
Quick dirty ugly solution
public static const millisecondsPerHour:int = 1000 * 60 * 60;
private function getHoursDifference(minDate:Date, maxDate:Date):uint {
return Math.ceil(( maxDate.getTime() - minDate.getTime()) / millisecondsPerHour);
}
Ok it sounds like you're talking about changing from a schedule or plan that's currently developed by a person using an excel spreadsheet and want to "computerize" the process. 1st Warning: "Scheduling is not trivial." How you store the time isn't all that important, but it is common to establish some level of granularity and convert the task time to integer multiples of this interval to simplify the scheduling task.
If you want to automate the process or simply error check you'll want to abstract things a bit. A basic weekly calendar with start and stop times, and perhaps shift info will be needed. An exception calendar would be a good idea to plan from the start. The exception calendar allows holidays and other exceptions. A table containing resource and capacity info will be needed. A table containing all the tasks to schedule and any dependencies between tasks will be needed. Do you want to consider concurrent requirements? (I need a truck and a driver...) Do you want to consider intermittent scheduling of resources? Should you support forward or backward scheduling? Do you plan to support what if scenarios? (Then you'll want a master schedule that's independent of the planning schedule(s)) Do you want to prioritize how tasks are placed on the schedule? (A lot of though is needed here depending on the work to be done.) You may very well want to identify a subset of the tasks to actually schedule. Then simply provide a reporting mechanism to show if the remaining work can fit into the white space in the schedule. (If you can't get the most demanding 10% done in the time available who cares about the other 90%)
2nd Warning: "If God wrote the schedule most companies couldn't follow it."