// Simple stupid concurrent Fibonacci microbenchmark.
// On my laptop I get:
// $ time ./concfib 30
// 1346269
// 
// real	0m7.673s
// user	0m17.332s
// sys	0m1.020s
// 
// This is (/ 1346269 7.673) = 175k leaf calls per second, which is (/
// 64000 175.0) = 370 times slower than the version just using
// function calls.  It does use both cores of my CPU, and 5.7
// microseconds is substantially faster than fork/exit/wait for a C
// program; forkovh.c measures that at 670 μs, over two orders of
// magnitude worse.
//
// This program can compute fib(32) = 3524578 in 1.7 gigabytes of RAM,
// suggesting that each goroutine needs less than a kilobyte.  But
// then, they aren’t all running at the same time.

package main

import (
	"fmt"
        "os"
        "strconv"
)

func fib(n int, ch chan int) {
        if n < 2 {
                ch <- 1
        } else {
               a := make(chan int)
               b := make(chan int)
               go fib(n-1, a)
               go fib(n-2, b)
               ch <- <-a + <-b
       }
}

func main() {
        n, err := strconv.Atoi(os.Args[1])
        if err != nil {
                panic(err)
        }
        ch := make(chan int)
        go fib(n, ch)
        fmt.Println(<-ch)
}