How to know when a task is done?

General Usage
,
1

If I create a Task using @async, and want to do something (like changing some status) immediately after that task is done, how do I do that? I guess istaskdone can only let me check everytime manually. I don’t quite understand notify & Condition, do they just notify me, or I can run some functions?

2

You can wait the task to finish.

3

How? I don’t want wait to block my following commands. What I want is scheduling a Task and then do my things. When the Task is done, it will notify me, or do more things, like writing some text to a file, etc.

4

Then you can simply create another Task, inside of which you wait for the previous task.

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6

Also you can just add this command inside your task

@async begin
   # commands of your original task
    # do something, when previous commands are complete
end
7

What do you mean by “notify me”?

1 Like
10

What do you mean by “notify me”?

Sorry if I was unclear. I want a Task that can handle some jobs for me while not blocking what I am doing ( @async ). But when that Task is done, I can immediately know it instead of checking with istaskdone each time manually. Also, I may want it to change the status of the job from Running to Succeeded or Failed , etc. And I may also want to do some other things immediately when the Task is done.
You can see my code here. I used @spawn to do this, but it is not the most simple way, I think.

11

Is this for use in an interactive Julia environment, or for a program to run by itself?

12

Both. I want it to be programmable as scripts and also interactive.

13

The problem is that, even with your clarification, “notify me” is ill defined. You are not your program after all - there is no automatic message queue or notification bar or something like that, you’ll have to create something that handles finished tasks for you. This is what @findmyway meant when they mentioned you have to create another Task that handles those for you. One way to achieve that is to have each task you spawned take e.g. a Channel to put results, errors etc. into and have a number of other tasks pull results out of that channel and act according to whatever that result is (e.g. spawn new tasks, write them to a file, etc.)

If you want it to work interactively, I’d look into ReplMaker.jl. You will have to decouple the interactive part from the standalone part, else your code will probably beome a lot harder to maintain.

14

Something like

@sync begin
    c = Condition()
    @async begin
        for i in 1:5
            println("I am doing work in the background...")
            sleep(0.5)
        end
        notify(c)
    end

    @async begin
        wait(c)
        println("I got notified")
    end
end

with output:

I am doing work in the background...
I am doing work in the background...
I am doing work in the background...
I am doing work in the background...
I am doing work in the background...
I got notified

?

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