Calculation of PI using multicores, http://www.soroushjp.com/2015/02/07/go-concurrency-is-not-parallelism-real-world-lessons-with-monte-carlo-simulations/

pi.go

package main

import (
  "fmt"
  "math/rand"
  "time"
  "runtime"
)

func init() {
  runtime.GOMAXPROCS(runtime.NumCPU())
  rand.Seed(time.Now().UnixNano())
}

func MultiPI(samples int) float64 {
  cpus := runtime.NumCPU()

  threadSamples := samples / cpus
  results := make(chan float64, cpus)
  fmt.Println(cpus);
  for j := 0; j < cpus; j++ {
      go func() {
          var inside int
          r := rand.New(rand.NewSource(time.Now().UnixNano()))
          for i := 0; i < threadSamples; i++ {
              x, y := r.Float64(), r.Float64()

              if x*x+y*y <= 1 {
                  inside++
              }
          }
          results <- float64(inside) / float64(threadSamples) * 4
      }()
  }

  var total float64
  for i := 0; i < cpus; i++ {
      total += <-results
  }

  return total / float64(cpus)
}


func main () {
      fmt.Println(MultiPI(1000000000))
}