pc_monitor.go

   1 /* pc_monitor.go */
   2
   3 package main
   4
   5 import (
   6         . "fmt"
   7         "crypto/rand"
   8         "time"
   9         . "sync"
  10 )
  11
  12 func random_between (begin, end int64) int64 {
  13         random_byte := make([]byte, 1)
  14         rand.Read(random_byte)
  15         return int64(random_byte[0]) % (end - begin + 1) + begin
  16 }
  17
  18 func random_sleep () {
  19         time.Sleep(random_between(0, MAX_SLEEP_TIME) * 10e7)
  20 }
  21
  22 func signal (channel chan int) {
  23         if len(channel) < cap(channel) || cap(channel) == 0 {
  24                 channel <- 0
  25         }
  26 }
  27
  28 func wait (channel chan int) {
  29         <-channel
  30 }
  31
  32 const (
  33         MAX_SLEEP_TIME = 5
  34         BUFFER_SIZE = 5
  35 )
  36
  37 type Monitor struct {
  38         mutex *Mutex
  39         empty, full chan int
  40         buffer []int
  41         front, rear, count int
  42 }
  43
  44 var monitor *Monitor
  45
  46 func newMonitor () *Monitor {
  47         return &Monitor {
  48                 new(Mutex),
  49                 make(chan int, BUFFER_SIZE),
  50                 make(chan int, BUFFER_SIZE),
  51                 make([]int, BUFFER_SIZE),
  52                 0, 0, 0 }
  53 }
  54
  55 func (m *Monitor) produce (i int) {
  56         m.mutex.Lock()
  57                 for m.count == BUFFER_SIZE {
  58                         m.mutex.Unlock()
  59                         wait(m.empty)    // (quase) uma variável de condição
  60                         m.mutex.Lock()
  61                 }
  62                 Println("producing:", i)
  63                 m.buffer[m.rear] = i
  64                 m.rear = (m.rear + 1) % BUFFER_SIZE
  65                 m.count++
  66                 signal(m.full)
  67         m.mutex.Unlock()
  68 }
  69
  70 func (m *Monitor) consume () {
  71         m.mutex.Lock()
  72                 for m.count == 0 {
  73                         m.mutex.Unlock()
  74                         wait(m.full)            // (quase) uma variável de condição
  75                         m.mutex.Lock()
  76                 }
  77                 v := m.buffer[m.front]
  78                 m.front = (m.front + 1) % BUFFER_SIZE
  79                 m.count--
  80                 Println("\t\t\tconsuming:", v)
  81                 signal(m.empty)
  82         m.mutex.Unlock()
  83 }
  84
  85 func producer () {
  86         for i := 0; ; i++ { // laço infinito
  87                 monitor.produce(i)
  88                 random_sleep()
  89         }
  90 }
  91
  92 func consumer () {
  93         for { // laço infinito
  94                 monitor.consume()
  95                 random_sleep()
  96         }
  97 }
  98
  99 func main () {
 100         monitor = newMonitor()
 101         go producer()
 102         go consumer()
 103         wait(make(chan int)) // espera indefinidamente
 104 }
 105