# How to define a function on all worker processes?
**URL:** https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117
**Category:** General Usage
**Tags:** parallel
**Created:** [June 6, 2017, 10:28pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117 "2017-06-06T22:28:12Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 6, 2017, 10:28pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/1 "2017-06-06T22:28:12Z")
I’m trying to run the following code on Julia 0.4.5 via Jupyter (so I can’t load files):
```julia
function foo()
return rand()
end
np = nprocs()
ap = 0
if np < CPU_CORES
ap = addprocs(CPU_CORES - np)
end
@everywhere bar = foo()
for x in ap
println(remotecall_fetch(x, () -> bar))
end
```
But I get the following exception:
```julia
On worker 9:
UndefVarError: foo not defined
in eval at ./sysimg.jl:14
in anonymous at multi.jl:1394
in anonymous at multi.jl:923
in run_work_thunk at multi.jl:661
[inlined code] from multi.jl:923
in anonymous at task.jl:63
in remotecall_fetch at multi.jl:747
in remotecall_fetch at multi.jl:750
in anonymous at multi.jl:1396
...and 6 other exceptions.
in sync_end at ./task.jl:413
in anonymous at multi.jl:1405
```
According to the documentation:
> You can force a command to run on all processes using the `@everywhere` macro. For example, `@everywhere` can also be used to directly define a function on all processes:
```julia
julia> @everywhere id = myid()
julia> remotecall_fetch(2, ()->id)
2
```
The docs aren’t very clear on how to actually define a function on all processes, and the example simply shows you how to run a function on all processes and then gets the return value.
---
### Author:  [@mohamed82008](https://discourse.julialang.org/u/mohamed82008)
#### Post date: [June 6, 2017, 10:34pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/2 "2017-06-06T22:34:37Z")
`@everywhere bar = foo()` defines the variable `bar` on all procs but only if the function `foo()` is available to all procs to define `bar`. The gist is use `@everywhere function foo()` when defining the function.
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 6, 2017, 10:56pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/3 "2017-06-06T22:56:28Z")
Thanks. The problem then is that the function is defined before the worker processes are started, and this will always be the case since we start/stop workers based on how much work is to be done. How do I pass an already defined function to a new worker?
---
### Author:  [@mohamed82008](https://discourse.julialang.org/u/mohamed82008)
#### Post date: [June 7, 2017, 12:01am UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/4 "2017-06-07T00:01:12Z")
Not sure how to do this. Let’s wait for someone more knowledgeable.
---
### Author:  [@Michael\_Eastwood](https://discourse.julialang.org/u/Michael_Eastwood)
#### Post date: [June 7, 2017, 1:00am UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/5 "2017-06-07T01:00:58Z")
I don’t know if this is the best way to do this or not, but here is a working example. Essentially you put all the functions you want your new worker to load into a separate file (`test.jl` in this example) and then instruct the worker to load that file.
```julia
shell> cat test.jl
f() = 1
julia> include("test.jl")
f (generic function with 1 method)
julia> f()
1
julia> addprocs(1)
1-element Array{Int64,1}:
2
julia> remotecall_fetch(f, 2)
ERROR: On worker 2:
UndefVarError: #f not defined
in deserialize_datatype at ./serialize.jl:823
in handle_deserialize at ./serialize.jl:571
in deserialize_msg at ./multi.jl:120
in message_handler_loop at ./multi.jl:1317
in process_tcp_streams at ./multi.jl:1276
in #618 at ./event.jl:68
in #remotecall_fetch#606(::Array{Any,1}, ::Function, ::Function, ::Base.Worker) at ./multi.jl:1070
in remotecall_fetch(::Function, ::Base.Worker) at ./multi.jl:1062
in #remotecall_fetch#609(::Array{Any,1}, ::Function, ::Function, ::Int64) at ./multi.jl:1080
in remotecall_fetch(::Function, ::Int64) at ./multi.jl:1080
julia> remotecall_fetch(include, 2, "test.jl")
f (generic function with 1 method)
julia> remotecall_fetch(f, 2)
1
```
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 7, 2017, 1:11am UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/6 "2017-06-07T01:11:32Z")
Unfortunately I’m running inside Jupyter with a read only filesystem, so I can’t create files.
---
### Author:  [@Michael\_Eastwood](https://discourse.julialang.org/u/Michael_Eastwood)
#### Post date: [June 7, 2017, 1:32am UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/7 "2017-06-07T01:32:39Z")
Oops, I missed that part of your post.
How about something like this:
```julia
julia> expr = quote
f() = 1
end
quote # REPL[1], line 2:
f() = begin # REPL[1], line 2:
1
end
end
julia> addprocs(1)
1-element Array{Int64,1}:
2
julia> remotecall_wait(eval, 2, expr)
Future(2,1,3,Nullable{Any}())
julia> fetch(@spawnat 2 f())
1
```
This feels like bad practice, but maybe it works in a pinch?
---
### Author:  [@bjarthur](https://discourse.julialang.org/u/bjarthur)
#### Post date: [June 7, 2017, 11:43am UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/8 "2017-06-07T11:43:03Z")
first off, why are you using julia 0.4.5 instead of 0.5.2 or even 0.6-rc2?
on \>0.5 you can simply say `@eval @everywhere bar = $(foo())`
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 7, 2017, 3:08pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/9 "2017-06-07T15:08:00Z")
Well, I mention this so often in bug reports that it should be my signature. We have customers that are change averse and we cannot expect them to upgrade very often. It took us several months to port all our code from 0.3 to 0.4 and given that 1.0 is imminent, we’ve decided to skip 0.5 and 0.6 and move straight to 1.0 which is expected to have long term support. If 0.6 is supposed to be forward compatible with 1.0, then we’ll consider moving to that sooner.
Will the above work in 1.0 as well?
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 7, 2017, 3:08pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/10 "2017-06-07T15:08:31Z")
Thanks that sounds promising.
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 7, 2017, 11:06pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/11 "2017-06-07T23:06:50Z")
I’m definitely making progress with this method. Still some complications because I’m using PyCall in the workers to call out to a python function, but I’ll figure that out. Thanks for your help.
---
### Author:  [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)
#### Post date: [June 9, 2017, 4:21pm UTC](https://discourse.julialang.org/t/how-to-define-a-function-on-all-worker-processes/4117/12 "2017-06-09T16:21:56Z")
So this worked really well. Specifically it was the only way for me to call `using ModuleName` in a worker process. Since my workers were started after I’d called `using` in the main process, none of the types made it through, so I had to call `using` separately in each worker.