# I don't get an error messages after a task/ thread failed
**URL:** https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255
**Category:** Internals & Design
**Created:** [March 20, 2020, 12:12pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255 "2020-03-20T12:12:22Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 20, 2020, 12:12pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/1 "2020-03-20T12:12:22Z")
Shouldn’t I get notified it a inner task fails?
---
### Author:  [@ffevotte](https://discourse.julialang.org/u/ffevotte)
#### Post date: [March 20, 2020, 3:06pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/2 "2020-03-20T15:06:01Z")
Yes you should:
```julia
julia> t = @async begin
sleep(1)
error("FAIL")
end
Task (runnable) @0x00007f0fd9203820
julia> fetch(t)
ERROR: TaskFailedException:
FAIL
Stacktrace:
[1] error(::String) at ./error.jl:33
[2] macro expansion at ./REPL[1]:3 [inlined]
[3] (::var"#5#6")() at ./task.jl:333
Stacktrace:
[1] wait at ./task.jl:251 [inlined]
[2] fetch(::Task) at ./task.jl:266
[3] top-level scope at REPL[2]:1
```
```julia
julia> t = Threads.@spawn begin
sleep(1)
error("FAIL")
end
Task (runnable) @0x00007f0fd92004f0
julia> fetch(t)
ERROR: TaskFailedException:
FAIL
Stacktrace:
[1] error(::String) at ./error.jl:33
[2] macro expansion at ./REPL[3]:3 [inlined]
[3] (::var"#7#8")() at ./threadingconstructs.jl:113
Stacktrace:
[1] wait at ./task.jl:251 [inlined]
[2] fetch(::Task) at ./task.jl:266
[3] top-level scope at REPL[4]:1
```
Or are we not speaking of the same thing?
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 20, 2020, 3:47pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/3 "2020-03-20T15:47:18Z")
Thank you for the quick anwser!
```julia
julia> Threads.@spawn @async error("Fail")
Task (done) @0x0000000010821fb0
```
I did this.
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [March 20, 2020, 3:56pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/4 "2020-03-20T15:56:42Z")
You need to fetch the result.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 20, 2020, 4:41pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/5 "2020-03-20T16:41:22Z")
Shouldn’t this fire anyway?
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [March 20, 2020, 8:04pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/6 "2020-03-20T20:04:32Z")
I think it should. We need structured concurrency for this:
[https://github.com/JuliaLang/julia/issues/33248](https://github.com/JuliaLang/julia/issues/33248)
Until we get structured concurrency, making sure to wrap `@async` and `@spawn` always with `@sync` is the closest thing you can do.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 23, 2020, 10:27am UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/7 "2020-03-23T10:27:03Z")
How would I use `@sync` here?
```julia
function t()
@async error("")
return 1
end
t()
```
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [March 23, 2020, 10:55am UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/8 "2020-03-23T10:55:00Z")
Either return the task and wait for it or put `@sync` in `t`. `@sync` syncs the tasks that are lexically enclosed.
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [March 23, 2020, 7:50pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/9 "2020-03-23T19:50:14Z")
Treating something like this safely requires so-called nursery (also known as task group and a few other names). ATM, if you want a task to live longer than the function creating it, you need to manually pass it back to the caller. It’s not safe (you may forget doing so). That’s why I think we need structured concurrency.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 24, 2020, 4:43pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/10 "2020-03-24T16:43:56Z")
I think I don’t mind the unstructured concurrency. But it’s very important to have a stacktrace if something fails! Where is the right place to say that?
---
### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [March 24, 2020, 6:24pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/11 "2020-03-24T18:24:03Z")
In what task should the error be thrown?
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 24, 2020, 9:14pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/12 "2020-03-24T21:14:45Z")
I think the whole program should stop running unless you started the task in a try-catch-block.
I think the error should be thrown in the most inner task and propagate out until it reaches a try-catch-block or crashes the program.
The stack trace should go from the occurred error through the started task and so on.
These are my first thoughts 🙂
---
### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [March 24, 2020, 9:15pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/13 "2020-03-24T21:15:43Z")
That is structured concurrency.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 24, 2020, 9:23pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/14 "2020-03-24T21:23:38Z")
Would this
```julia
function f()
@async sleep(10)
return 1
end
try f() |> println catch end
dont_have_to_wait_and_do_the_next_thing()
```
still work with structured concurrency?
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [March 24, 2020, 9:41pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/15 "2020-03-24T21:41:11Z")
You’d write something like
```julia
function f(nursery)
@async nursery sleep(10)
return 1
end
try
withnursery() do nursery
f(nursery) |> println
dont_have_to_wait_and_do_the_next_thing()
end
catch
end
```
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 24, 2020, 9:49pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/16 "2020-03-24T21:49:27Z")
I don’t understand the syntax. What is `withnursery()` and where is it defined?
The syntax gets more complicated. What’s the point against:
> [@Impressium](#):
>
> I think the whole program should stop running unless you started the task in a try-catch-block.
>
> I think the error should be thrown in the most inner task and propagate out until it reaches a try-catch-block or crashes the program.
>
> The stack trace should go from the occurred error through the started task and so on.
>
> These are my first thoughts 🙂
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [March 24, 2020, 10:04pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/17 "2020-03-24T22:04:21Z")
It’s bad because the caller can’t tell if your function or _any_ function that might exist in the call stack starting from your function may leak un-synchronized tasks; i.e., it violates so-called “black box rule”.
For more information, please have a look at Julep [Juleps/StructuredConcurrency.md at master · JuliaLang/Juleps · GitHub](https://github.com/JuliaLang/Juleps/blob/master/StructuredConcurrency.md) and the discussion in the PR. Your point is related to this discussion on effect system which is effectively a dynamically-scoped nursery: [Taking Structured Concurrency Seriously · Issue #33248 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/33248#issuecomment-573365469)
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 24, 2020, 10:09pm UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/18 "2020-03-24T22:09:37Z")
I’m not sure, what I want. Both sites have their benefits…
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 27, 2020, 8:29am UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/19 "2020-03-27T08:29:17Z")
This is my solution as far:
```julia
macro my_async(ex)
quote
@async try $(esc(ex))
catch e
println("IN @my_async")
# Here I would like to get the definition line number of `ex`
@show e
end
end
end
```
So now I get feedback if a task fails.
---
### Author:  [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)
#### Post date: [March 27, 2020, 8:50am UTC](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255/20 "2020-03-27T08:50:52Z")
FWIW, you can improve the error printing with
```julia
macro my_async(ex)
quote
@async try
$(esc(ex))
catch e
println("In task:")
@error(exception = (e, catch_backtrace()))
end
end
end
```
[Next page](https://discourse.julialang.org/t/i-dont-get-an-error-messages-after-a-task-thread-failed/36255.md?page=2)