# How to coordinate shutting down tasks?
**URL:** https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434
**Category:** New to Julia
**Tags:** question, task
**Created:** [December 8, 2025, 3:17pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434 "2025-12-08T15:17:08Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@freeman](https://discourse.julialang.org/u/freeman)
#### Post date: [December 8, 2025, 3:17pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/1 "2025-12-08T15:17:08Z")
I use tasks to decouple subscribing to data streams and publish downstream data streams. I also use Bool references to coordinate when all tasks should exit.
Schematically, it looks like this:
```julia-auto
# main thread
run_flag = Threads.Atomic{Bool}(true)
# task1, subscribe
try
while run_flag[]
for msg in producerthing
push!(channel, msg)
end
end
catch # if error set flag to end all other tasks
run_flag[] = false
end
# task2, worker
while run_flag[]
msg = take!(channel)
# do stuff
end
```
This kind of works.
However, it has at least one failure mode: If task1 dies and calls `run_flag[] = false` and channel happens to be empty, then task2 will be waiting on the channel forever and never check that the `run_flag` has been set to false.
Are thread-safe boolean flags the correct way to coordinate this work? If yes, how would you implement this idea correctly? If not, how would you do it instead?
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [December 8, 2025, 3:29pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/2 "2025-12-08T15:29:43Z")
When I did something similar a few years ago, I put a termination message (or rather one message per task) on the channel. Since the normal messages contained a positive integer, I could conveniently encode the termination messages with a negative value.
---
### Author:  [@freeman](https://discourse.julialang.org/u/freeman)
#### Post date: [December 8, 2025, 3:36pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/3 "2025-12-08T15:36:22Z")
Ok but in reality I have not just 2 tasks.
Imagine 5 tasks push!ing into the channel and one take!ing from it. If one of the pushing tasks crashes, how does it tell the other pushing tasks to exit? Or if I CTRL-C how do I coordinate that all tasks should exit? My design handles these cases (but has the same problematic edge case I described).
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [December 8, 2025, 3:45pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/5 "2025-12-08T15:45:23Z")
My case was certainly easier with a tree structure on the tasks and a dedicated channel for each group of workers.
What about both using an atomic Bool and sending a message to all downstream tasks when shutting down. It doesn’t even have to be a special message, just something to wake them up.
---
### Author:  [@freeman](https://discourse.julialang.org/u/freeman)
#### Post date: [December 8, 2025, 3:45pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/6 "2025-12-08T15:45:54Z")
Yes, that’s what I do as you can see from my example. It has a problem which I describe and haven’t been able to solve yet. EDIT: I think the person I was responding to removed their message?
---
### Author:  [@freeman](https://discourse.julialang.org/u/freeman)
#### Post date: [December 8, 2025, 3:46pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/7 "2025-12-08T15:46:45Z")
Ah, an atomic Bool from subscriber to subscriber, but a special message to downstream? I suppose could work. Not elegant though, right?
---
### Author:  [@freeman](https://discourse.julialang.org/u/freeman)
#### Post date: [December 8, 2025, 3:53pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/8 "2025-12-08T15:53:16Z")
I also have a non-elegant solution, which is to `close(channel)`. Then I need a try/except because take!ing from a closed channel triggered an InvalideStateException. It feels like a hack though.
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [December 8, 2025, 4:15pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/9 "2025-12-08T16:15:42Z")
I’m just an amateur at multi-task programming, so all I can say is that my approach worked very nicely for my use case. But I never had to catch any exceptions and all shutdown was initiated due to the work being completed.
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [December 8, 2025, 4:20pm UTC](https://discourse.julialang.org/t/how-to-coordinate-shutting-down-tasks/134434/10 "2025-12-08T16:20:34Z")
> [@freeman](#):
>
> I also have a non-elegant solution, which is to `close(channel)`. Then I need a try/except because take!ing from a closed channel triggered an InvalideStateException. It feels like a hack though.
I think this is likely the cleanest it can be with the current API. Unfortunately, `take!` doesn’t return a `Union{T, ChannelClosed}` or some other useful sum type that can communicate that the channel is closed intentionally.