# Calling another function in loop using Base.Threads
**URL:** https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037
**Category:** General Usage
**Tags:** multithreading
**Created:** [July 30, 2022, 3:55pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037 "2022-07-30T15:55:50Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Amol\_H](https://discourse.julialang.org/u/Amol_H)
#### Post date: [July 30, 2022, 3:55pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/1 "2022-07-30T15:55:50Z")
Dear All,
I am having a problem running the following code in parallel. Please suggest how to achieve the parallelization to populate an array by a so-called very computationally expensive function.
Thanks and Regards
Amol
```julia
#!/usr/bin/julia
using Base.Threads
using LinearAlgebra,NumericalIntegration
x = collect(0:1e-6:1);
function test_func(a)
return a*a;
end
test = zeros(length(x));
Threads.@threads for i = 0:length(x)
test[i] = test_func(x[i]);
end
println("integrate = ", integrate(x,test) );
println(" ");
```
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [July 30, 2022, 4:03pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/2 "2022-07-30T16:03:11Z")
> [@Amol\_H](#):
>
> I am having a problem running the following code in parallel.
what problem?
> [@Amol\_H](#):
>
> ```julia
> test = zeros(length(x));
>
> Threads.@threads for i = 0:length(x)
> test[i] = test_func(x[i]);
> end
>
> ```
this is gonna be slow, you’re running code in global with non-constant global variable
---
### Author:  [@Amol\_H](https://discourse.julialang.org/u/Amol_H)
#### Post date: [July 30, 2022, 4:04pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/3 "2022-07-30T16:04:18Z")
```julia
ERROR: LoadError: TaskFailedException
Stacktrace:
[1] wait
@ ./task.jl:334 [inlined]
[2] threading_run(func::Function)
@ Base.Threads ./threadingconstructs.jl:38
[3] top-level scope
@ ./threadingconstructs.jl:97
nested task error: BoundsError: attempt to access 1000001-element Vector{Float64} at index [0]
Stacktrace:
[1] getindex(A::Vector{Float64}, i1::Int64)
@ Base ./array.jl:861
[2] macro expansion
@ ~/TestProg/threads.jl:15 [inlined]
[3] (::var"#2#threadsfor_fun#1"{UnitRange{Int64}})(onethread::Bool)
@ Main ./threadingconstructs.jl:85
[4] (::var"#2#threadsfor_fun#1"{UnitRange{Int64}})()
@ Main ./threadingconstructs.jl:52
in expression starting at /home/amol/TestProg/threads.jl:14
```
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 30, 2022, 4:05pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/4 "2022-07-30T16:05:51Z")
> [@Amol\_H](#):
>
> `Threads.@threads for i = 0:length(x)`
Julia `Array`s have one-based indexing, and use inclusive ranges.
Use `1:length(x)` or, preferably, `eachindex(x)`
---
### Author:  [@Amol\_H](https://discourse.julialang.org/u/Amol_H)
#### Post date: [July 30, 2022, 4:06pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/5 "2022-07-30T16:06:03Z")
I am new to these ‘Threads’. How to exactly achieve the same using Base.Threads package? I would be really grateful for your help in this regard.
---
### Author:  [@Amol\_H](https://discourse.julialang.org/u/Amol_H)
#### Post date: [July 30, 2022, 4:07pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/6 "2022-07-30T16:07:34Z")
Thanks! Gotcha…solved it. 😃
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 30, 2022, 4:09pm UTC](https://discourse.julialang.org/t/calling-another-function-in-loop-using-base-threads/85037/7 "2022-07-30T16:09:18Z")
But also make sure to put your code in functions, otherwise, threads will be slow.