Add Julia implementation using OhMyThreads.jl

[giordano]

OhMyThreads.jl is a new-ish package which provides user-friendly threading constructs, for example it comes with a multithreaded map reduce, which is perfect for this program. Compare the implementation in this PR

pi_examples/julia_ohmythreads_pi_dir/pi.jl

Lines 11 to 17 in bdd72c1

	function _picalc(numsteps)
	slice = 1 / numsteps
	return tmapreduce(+, 1:numsteps; ntasks=nthreads()) do i
	4.0 / (1.0 + ((i - 0.5) * slice) ^ 2)
	end * slice
	end

with the current multithreaded implementation:

pi_examples/julia_threads_dir/pi.jl

Lines 5 to 21 in fc92267

	function _picalc(numsteps)
	slice = 1.0 / numsteps
	sums = zeros(Float64, nthreads())
	n = cld(numsteps, nthreads())
	Threads.@threads for i in 1:nthreads()
	sum_thread = 0.0
	@simd for j in (1 + (i - 1) * n):min(numsteps, i * n)
	x = (j - 0.5) * slice
	sum_thread += 4.0 / (1.0 + x ^ 2)
	end
	sums[threadid()] = sum_thread
	end
	return sum(sums) * slice
	end

Some benchmarks: on Nvidia Grace-Grace, with this implementation using Julia v1.11.1 I get

$ julia -t 144 pi.jl 1000000000000
  Activating project at `~/repo/pi_examples/julia_ohmythreads_dir`
  No Changes to `~/repo/pi_examples/julia_ohmythreads_dir/Project.toml`
  No Changes to `~/repo/pi_examples/julia_ohmythreads_dir/Manifest.toml`
  Warming up...done. [0.195s]

Calculating PI using:
  1000000000000 slices
  144 thread(s)
Obtained value of PI: 3.1415926535897936
Time taken: 5.458 seconds

With julia_threads_pi_dir (same version of Julia as above):

$ julia -t 144 pi.jl 1000000000000
  Warming up...done. [0.095s]

Calculating PI using:
  1000000000000 slices
  144 thread(s)
Obtained value of PI: 3.141592653588557
Time taken: 5.441 seconds

With c_omp_pi_dir:

$ make -B CC=gcc COPTS='-O2 -fopenmp -march=native' && OMP_NUM_THREADS=144 ./pi 1000000000000
gcc -O2 -fopenmp -march=native  -c pi.c -o pi.o
gcc -O2 -fopenmp -march=native  -o pi pi.o
Calculating PI using:
  1000000000000 slices
  144 thread(s)
Obtained value for PI: 3.14159265358896
Time taken:            5.77358439611271 seconds
$ gcc --version
gcc (GCC) 14.1.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

With fortran_omp_pi_dir:

$ make -Bf Makefile.gfortran FOPT='-O2 -fopenmp -march=native' && ./pi 1000000000000
gfortran -O2 -fopenmp -march=native -o pi pi.f90
Calculating PI using:
                     1000000000000 slices
                               144 OpenMP threads
Obtained value of PI: 3.1415926536
Time taken:                5.72090 seconds
$ gfortran --version
GNU Fortran (GCC) 14.1.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.