I have a requirement to execute a small set of related tasks on a custom thread created for them. The tasks will be scheduled from different classes.
I'm planning to use GCD's dispatch_queue_create to create the custom thread and schedule the task on it. Note that all the related tasks must execute only on that one thread in order.So my question is if I call dispatch_queue_create("my_custom_thread_label", NULL) with the same label from many classes in my codebase, would it all eventually map to just one thread? Or do I need to create it in one place and get a reference to it whenever needed? Thanks.
You need to create it in one place and pass the pointer around.
Related
I have used one multi instance subprocess which includes an workflow with human task. When executing, its creating the number of human tasks as to the number of elements present inside the collection object. But all tasks have same process instance id. How the relation is working between parent process and multi instance subprocess?
If there are multiple elements in collection list, then it will create those many tasks inside the multi instance sub process. As all the tasks have same process instance id, how to identify the respective process variable values for each task and the uniqueness of each flow afterwards? And is there a way to make it create an different instance id for each task of the multi instance subprocess?
I did not get all the question, but I will try to answer what I got:
Human tasks have their own task instance id
What is collection object? If you mean tasks in bpmn model, then it is as expected: process instance flow starts after start node and when it reaches a human task, it will create an task instance with id. You can see it in the tasks in UI and with api you can claim, work on, complete , populate data etc.
it is wise to have a separate/different variable for every tasks that can execute in parallel. Then the input will be kept in distinguished data placeholders and you can use it accordingly.
you can create a different instance(task instance) for each task or have repeatable tasks
well the answer was to put the multi-instance into a sub-process, this will allow me to have a separate process instance id per each element of the my List (the input of the multi-instance )
I have a program, it loads a few tasks from a file prepared by user and start executing them according the scheduling shown in the file.
Example: taskFile.txt
Task1: run every hour
Task2: run every 2 seconds
...
TaskN: run every monday at 10:00
This first part is Ok, i solved by using ScheduledExecutorService and i am very satisfied. The tasks are load and run as they should.
Now, let's image that the user, by GUI (at runtime), decides that Task2 should run every minute, and he wants to remove Task3.
I cannot find any way to access one specific task in the pool, in order to remove/modify it.
So I cannot update tasks at runtime. When user changes a task, I can only modify the taskFile.txt and restart the application, in order to reload all tasks according the newly updated taskFile.txt.
Do you know any way to access a single task in order to modify/delete it?
Or even, a way to remove one given task, so i can insert a new one in the pool, with the modifications wanted by the user.
Thanks
This is not elegant, but works.
Let's suppose you need 10 threads, and sometimes you need to manage a specific thread.
Instead to have a pool with 10 thread, use 10 pools with one thread for each, keep them in your favourite data structure, and act on the pool_1 when you want to modify thread_1.
It's possible to remove the older Runnable from the pool and put a new one with the needed changes.
Otherways, anything put in the pool became anonymous and will be not directly manageable.
If somebody has a better solution...
I'm working on a project with Quartz and has been a problem with the dependencies with jobs.
we have a setup where A and B aren't dependent on eachother, though C is:
A and B can run at the same time, but C can only run when both A and B are complete.
Is there a way to set this kind of scenario up in Quartz, so that C will only trigger when A and B finish?
Not directly AFAIK, but it should be not too hard to use a TriggerListener to implement such a functionality (a TriggerListener is run both a start and end of jobs, and you can set them up for individual triggers or trigger groups).
EDIT: there is even a specific FAQ Topic about this problem:
There currently is no "direct" or "free" way to chain triggers with
Quartz. However there are several ways you can accomplish it without
much effort. Below is an outline of a couple approaches:
One way is to use a listener (i.e. a TriggerListener, JobListener or
SchedulerListener) that can notice the completion of a job/trigger and
then immediately schedule a new trigger to fire. This approach can get
a bit involved, since you'll have to inform the listener which job
follows which - and you may need to worry about persistence of this
information. See the listener
org.quartz.listeners.JobChainingJobListener which ships with Quartz -
as it already has some of this functionality.
Another way is to build a Job that contains within its JobDataMap the
name of the next job to fire, and as the job completes (the last step
in its execute() method) have the job schedule the next job. Several
people are doing this and have had good luck. Most have made a base
(abstract) class that is a Job that knows how to get the job name and
group out of the JobDataMap using pre-defined keys (constants) and
contains code to schedule the identified job. This abstract Job's
implementation of execute() delegates to an abstract template method
such as "doWork()" (where the extending Job class's real work goes)
and then it contains the code for scheduling the follow-up job. Then
they simply make extensions of this class that included the work the
job should do. The usage of 'durable' jobs, or the overloaded
addJob(JobDetail, boolean, boolean) method (added in Quartz 2.2) helps
the application define all the jobs at once with their proper data,
without yet creating triggers to fire them (other than one trigger to
fire the first job in the chain).
In the future, Quartz will provide a much cleaner way to do this, but
until then, you'll have to use one of the above approaches, or think
of yet another that works better for you.
I am working on a Windows service which needs to schedule tasks whenever one of it's web services is called. This could happen hundreds of times per second in a worst case scenario. The task needs to wait a period of time, typically a minute or two, then call a method passing a parameter.
We tried to build our own scheduler class to do this:
public void ScheduleTask<T>(TimeSpan delay, Action<T> task, T arg)
{
Thread.Sleep(delay);
threadPool.ExecuteAsync(task, arg);
}
But we figured this wouldn't be appropriate because we could theoretically end up with hundreds of Thread Pool threads all waiting. I am under the impression that there is a finite number of Thread Pool threads available and that this could potentially lock up the system.
I then turned to Quartz.NET and read on their features page that:
Job class instances can be instantiated by Quartz.NET, or by your application's framework.
and on page 3 of their tutorial that the Scheduler creates instances of your Job class (not you) and as such:
it does not make sense to have data-members defined on the job class as their values would be 'cleared' every time the job executes.
Feel free to yell at me, but how do I get a reference to my Job class instance before it executes so I can set a property on it?
The property is doing the job of a
parameter so i have no interest in it
after the Job has executed.
I also want to minimise the number of
objects it takes to acheive this to
keep my code neat and simple.
Finally, I seriously dislike using
Dictionaries so would prefer to avoid the JobDataMap object.
I don't understand exactly what your use case is and why you would need to set a property on the job, but to answer your question: to get access to your job before it executes you need to create a job listener (implement IJobListener). The job listener gets called just before the job gets executed, so you could set a property at that point.
Some links:
The documentation on job listeners
I wrote a blog post detailing the creation of listeners, here.
I have a simple custom activity with a private member variable (integer).
When i put it inside a sequence activity which is inside a while activity and start iterating i have a problem:
My member variable is zeroed in each iteration even though i increment it by one every time the activity is executed.
What am i doing wrong?
Thanks,
Adi Barda
Without seeing the code it is hard to say, but when you are working inside of a While activity you have to be careful how you modify state on your child activities. The While activity spawns multiple execution execution contexts and will clone your activity from a template (in other words - you aren't executing the same activity multiple times, the workflow creates multiple instances of your custom activity). See: http://blogs.msdn.com/advancedworkflow/archive/2006/03/21/557121.aspx and http://msdn.microsoft.com/en-us/magazine/cc163414.aspx