# Illustration of Cigarette Smokers Problem in Golang

Assume a cigarette requires three ingredients to make and smoke: tobacco, paper, and matches. There are three smokers around a table, each of whom has an infinite supply of one of the three ingredients — one smoker has an infinite supply of tobacco, another has paper, and the third has matches. A fourth party, with an unlimited supply of everything, chooses at random a smoker, and put on the table the supplies needed for a cigarrette. The chosen smoker smokes, and the process should repeat indefinitely.

### Example

``````package main

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

const (
paper = iota
grass
match
)

var smokeMap = map[int]string{
paper: "paper",
grass: "grass",
match: "match",
}

var names = map[int]string{
paper: "Sandy",
grass: "Apple",
match: "Daisy",
}

type Table struct {
paper chan int
grass chan int
match chan int
}

func arbitrate(t *Table, smokers [3]chan int) {
for {
time.Sleep(time.Millisecond * 500)
next := rand.Intn(3)
fmt.Printf("Table chooses %s: %s\n", smokeMap[next], names[next])
switch next {
case paper:
t.grass <- 1
t.match <- 1
case grass:
t.paper <- 1
t.match <- 1
case match:
t.grass <- 1
t.paper <- 1
}
for _, smoker := range smokers {
smoker <- next
}
wg.Wait()
}
}

func smoker(t *Table, name string, smokes int, signal chan int) {
var chosen = -1
for {
chosen = <-signal // blocks

if smokes != chosen {
continue
}

fmt.Printf("Table: %d grass: %d match: %d\n", len(t.paper), len(t.grass), len(t.match))
select {
case <-t.paper:
case <-t.grass:
case <-t.match:
}
fmt.Printf("Table: %d grass: %d match: %d\n", len(t.paper), len(t.grass), len(t.match))
time.Sleep(10 * time.Millisecond)
select {
case <-t.paper:
case <-t.grass:
case <-t.match:
}
fmt.Printf("Table: %d grass: %d match: %d\n", len(t.paper), len(t.grass), len(t.match))
fmt.Printf("%s smokes a cigarette\n", name)
time.Sleep(time.Millisecond * 500)
wg.Done()
time.Sleep(time.Millisecond * 100)
}
}

const LIMIT = 1

var wg *sync.WaitGroup

func main() {
wg = new(sync.WaitGroup)
table := new(Table)
table.match = make(chan int, LIMIT)
table.paper = make(chan int, LIMIT)
table.grass = make(chan int, LIMIT)
var signals [3]chan int
// three smokers
for i := 0; i < 3; i++ {
signal := make(chan int, 1)
signals[i] = signal
go smoker(table, names[i], i, signal)
}
fmt.Printf("%s, %s, %s, sit with \n%s, %s, %s\n\n", names[0], names[1], names[2], smokeMap[0], smokeMap[1], smokeMap[2])
arbitrate(table, signals)
}``````

### Output

``````Sandy, Apple, Daisy, sit with
paper, grass, match

Table chooses match: Daisy
Table: 1 grass: 1 match: 0
Table: 1 grass: 0 match: 0
Table: 0 grass: 0 match: 0
Daisy smokes a cigarette
Table chooses paper: Sandy
Table: 0 grass: 1 match: 1
Table: 0 grass: 1 match: 0
Table: 0 grass: 0 match: 0
Sandy smokes a cigarette
Table chooses match: Daisy
Table: 1 grass: 1 match: 0
Table: 1 grass: 0 match: 0
Table: 0 grass: 0 match: 0
Daisy smokes a cigarette``````