# Sequencing for distributed for-loop
**URL:** https://discourse.julialang.org/t/sequencing-for-distributed-for-loop/18930
**Category:** General Usage
**Tags:** parallel
**Created:** [December 22, 2018, 9:00pm UTC](https://discourse.julialang.org/t/sequencing-for-distributed-for-loop/18930 "2018-12-22T21:00:58Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@tk3369](https://discourse.julialang.org/u/tk3369)
#### Post date: [December 22, 2018, 9:00pm UTC](https://discourse.julialang.org/t/sequencing-for-distributed-for-loop/18930/1 "2018-12-22T21:00:58Z")
Is it possible to make `@distributed` do the work and respect the original order?
```julia
using Distributed
addprocs(2)
process_dates = range(Date(2018, 12, 20), stop = Date(2018, 12, 1), step = -Dates.Day(1))
@sync @distributed for i in process_dates
println(i)
sleep(1)
end
end
```
It goes like this:
```julia
| From worker 3:|2018-12-10|
| From worker 2:|2018-12-20|
| From worker 3:|2018-12-09|
| From worker 2:|2018-12-19|
| From worker 3:|2018-12-08|
| From worker 2:|2018-12-18|
| From worker 3:|2018-12-07|
| From worker 2:|2018-12-17|
| From worker 3:|2018-12-06|
| From worker 2:|2018-12-16|
| From worker 3:|2018-12-05|
| From worker 2:|2018-12-15|
| From worker 3:|2018-12-04|
| From worker 2:|2018-12-14|
| From worker 3:|2018-12-03|
| From worker 2:|2018-12-13|
| From worker 3:|2018-12-02|
| From worker 2:|2018-12-12|
| From worker 3:|2018-12-01|
| From worker 2:|2018-12-11|
```
However, I would rather see it goes like this:
```julia
| From worker 3:|2018-12-19|
| From worker 2:|2018-12-20|
| From worker 3:|2018-12-17|
| From worker 2:|2018-12-18|
| From worker 3:|2018-12-15|
| From worker 2:|2018-12-16|
...
```
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [December 23, 2018, 11:39am UTC](https://discourse.julialang.org/t/sequencing-for-distributed-for-loop/18930/2 "2018-12-23T11:39:16Z")
I don’t think you can control this directly:
```julia
julia> @macroexpand @sync @distributed for i ∈ 1:10; print(i); end
begin
#= task.jl:246 =#
let ##sync#72 = (Base.Any)[]
#= task.jl:247 =#
#154#v = begin
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:337 =#
local #155#ref = (Distributed.pfor)(begin
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:289 =#
function (#156#R, #157#lo::Distributed.Int, #158#hi::Distributed.Int)
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:290 =#
for i = #156#R[#157#lo:#158#hi]
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:291 =#
begin
#= C:\Users\Nils-Holger\Desktop\KoalaTest.jl:28 =#
print(i)
end
end
end
end, 1:10)
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:338 =#
if $(Expr(:isdefined, Symbol("##sync#72")))
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:339 =#
(Distributed.push!)(##sync#72, #155#ref)
end
#= C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v0.7\Distributed\src\macros.jl:341 =#
#155#ref
end
#= task.jl:248 =#
(Base.sync_end)(##sync#72)
#= task.jl:249 =#
#154#v
end
end
```
So this uses `Distributed.pfor`, in stdlib\v0.7\Distributed\src\macros.jl:
```julia
function pfor(f, R)
@async @sync for c in splitrange(length(R), nworkers())
@spawn f(R, first(c), last(c))
end
end
```
so in my example `splitrange(length(1:10), 2)` would be called, returning a vector holding `[1:5, 6:10]`, and worker 2 then gets allocated `1:5`, worker 3 gets `6:10` and the output therefore alternates `1,6,2,7,...`
One way of “preserving” the natural order would be to make the range going into the loop such that it alternates, i.e. `vcat(collect(1:2:9), collect(2:2:10))` instead of simply `1:10` - although I think you still might end up with worker 3 starting first, and therefore an output of `2,1,4,3,...` rather than `1,2,3,4,...`