# L-11 MCS 507 Fri 15 Sep 2023 : estimatepimt.jl

# Multithreaded version of a Monte Carlo simulation.
# At the command prompt type for example:
# time JULIA_NUM_THREADS=8 julia estimatepimt.jl
# to run the code with 8 threads.

using Base.Threads
import Statistics

myrand(x::Int64) = (1103515245x + 12345) % 2^31

"""
    function estimatepi(n)

Runs a simple Monte Carlo method
to estimate pi with n samples.
"""
function estimatepi(n)
   r = threadid()
   count = 0
   for i=1:n
       r = myrand(r)
       x = r/2^31
       r = myrand(r)
       y = r/2^31
       count += (x^2 + y^2) <= 1
   end
   return 4*count/n
end

nt = nthreads()
println("The number of threads : $nt")
estimates = zeros(nt)

timestart = time()
@threads for i=1:nt
    estimates[i] = estimatepi(10_000_000_000/nt) 
end
estpi = Statistics.mean(estimates)
elapsed = time() - timestart

println("The estimate for Pi : $estpi")
println("The elapsed time : $elapsed seconds")