# Timedwait() doesn't time out

**URL:** <https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182>\
**Category:** New to Julia\
**Tags:** task\
**Created:** [November 9, 2021, 6:27am UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182 "2021-11-09T06:27:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![kykim0](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kykim0/32/30612_2.png) [@kykim0](https://discourse.julialang.org/u/kykim0)\
**Post date:** [November 9, 2021, 6:27am UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182/1 "2021-11-09T06:27:04Z")

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I’m new to Julia’s multi-threading and frankly Julia itself. I’ve been reading up on the API docs and trying various things on REPL. In particular, I was playing with the `timedwait()` method which IIUC runs a given function either until it finishes or the deadline has been reached. So to test my understanding I did:

```julia
julia> function test()                                                                                                                                  
         sleep(2)                                                                                                                                       
         return true                                                                                                                                    
       end                                                                                                                                              
test (generic function with 1 method)

julia> timedwait(test, 1.0)                                                                                                                             
:ok

```

In other words, I defined a function that simply sleeps for 2 seconds and returns true. And I ran `timedwait()` on that method with a timeout of 1.0, but this returned `:ok`. What am I missing here?

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [November 9, 2021, 10:40pm UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182/2 "2021-11-09T22:40:07Z")

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The callback function is called multiple times (until returning true). Your function always return true so `timedwait` returns `:ok`. I agree that the docstring for `timedwait` isn’t very clear though so would be good to improve that.

Here is an example:

```julia
julia> cb = function()
           @info "Callback called"
           return false # always false so this will time out
       end;

julia> timedwait(cb, 1.0)
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
[ Info: Callback called
:timed_out

```

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**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 10, 2021, 2:02am UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182/3 "2021-11-10T02:02:32Z")

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So it seems like the intended purpose is for the callback function to check if something is available in a Channel or if a mutex has been released or whatever, and then if it has finally return true, otherwise return false. Then when the timeout occurs, you can kill the task that was supposed to provide the value to the channel or similar?

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**Author:** ![kykim0](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kykim0/32/30612_2.png) [@kykim0](https://discourse.julialang.org/u/kykim0)\
**Post date:** [November 10, 2021, 4:59am UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182/4 "2021-11-10T04:59:45Z")

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What I was hoping to do was to run a series of simulations in parallel using `Threads.@spawn`, and use `@sync` to wait for the simulations to finish, but not for more than a certain timeout. My initial thought was to do sth like the following:

```julia
function run_simulations()
  @sync for i = 1:n
    Threads.@spawn simulate()
  end
end

timedwait(run_simulations, timeout)

```

But based on @fredrikekre’s answer the above doesn’t quite do what I wanted as the callback gets called continuously. Is there an easy way to achieve this with basic Julia APIs? Perhaps store references to the `Task`s returned from the `@spawn` calls and continuously check if everything is done inside the callback?

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<div class="post-metadata">

**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 10, 2021, 4:17pm UTC](https://discourse.julialang.org/t/timedwait-doesnt-time-out/71182/5 "2021-11-10T16:17:14Z")

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I think what you want is that your `simulate()` code should check to see if it has been sent a message to terminate prematurely (on a Channel).

> [@kykim0](#):
>
> store references to the `Task` s returned from the `@spawn` calls and continuously check if everything is done inside the callback?

Yes, do this, then run timedwait and at the end of the timeout if the callback hasn’t collected all the results, send the “abort” message over the channel to the simulate code.

What this seems to do is avoid an unsafe exit via “throw an exception” into the task… potentially leaving things in an inconsistent state and preventing further safe computation. I’m not clear on if there’s a safe way to simply “kill” a task.