How to run two functions simultaneously in julia? - multiprocessing

Question

I'm trying to run two functions simultaneously in julia, but I don't know how to do it. Here you can see my code:
function area(side::Float64)
return side*side
end
function f(n::Int64)
mat = zeros(n,n)
for i=1:n
for j=1:n
mat[i,j] = area(rand())
end
end
return mat
end
function g(n::Int64)
mat = zeros(n,n)
for i=1:n
for j=1:n
mat[i,j] = area(rand()*rand())
end
end
return mat
end
s1 = f(10)
s2 = g(10)
hcat(s1,s2)

Answer 1

In Julia 1.3 you can spawn tasks that will get scheduled on different threads using Threads.#spawn:
begin
s1 = Threads.#spawn f(10)
s2 = Threads.#spawn g(10)
s1 = fetch(s1)
s2 = fetch(s2)
end
See the announcement blog post for more info: https://julialang.org/blog/2019/07/multithreading.

Answer 2

Generally, there are different notions of "simultaneous" in parallel computing.
Since you tagged your question as "multiprocessing" let me give you a straightforward multi process solution (which should work for any Julia version >= 0.7). As such, it utilizes Julias built-in Distributed computing tools.
using Distributed
nworkers() < 2 && addprocs(2) # add two worker processes if necessary
#everywhere begin # define your functions on both workers
area(side::Float64) = side*side
function f(n::Int64)
mat = zeros(n,n)
for i=1:n
for j=1:n
mat[i,j] = area(rand())
end
end
return mat
end
function g(n::Int64)
mat = zeros(n,n)
for i=1:n
for j=1:n
mat[i,j] = area(rand()*rand())
end
end
return mat
end
end
# spawn tasks on the two workers (non-blocking)
t1 = #spawn f(10)
t2 = #spawn g(10)
# fetch the results (blocking until workers have finished)
r1 = fetch(t1)
r2 = fetch(t2)
hcat(r1,r2)
For more on how to use Distributed for parallel computing checkout, for example, this part of the Julia documentation or this Jupyter workshop from one of my workshops: Parallel Computing in Julia.