Channelsのselect

sample.go

package main

import (
  "fmt"
  "time"
)

const CAP = 20

func main() {
  callFibonacciWithDefault()
  callFibonacciWithoutDefault()
}

func fibonacciWithDefault( c, c1, quit chan int ) {
  x, y := 0, 1

  for {
    select {
    case c <- x:
      x, y = y, x + y
    case <- quit:
      fmt.Println( "quit" )
      return
    default:
      // fmt.Println( "default" )
      i, ok := <- c1

      if ok {
        fmt.Println( "start?", i )
        time.Sleep( 100 * time.Millisecond )
      }
    }
  }
}

func callFibonacciWithDefault() {
  c    := make( chan int )
  quit := make( chan int )
  c1   := make( chan int )

  go func() {
    c1 <- 1
    close( c1 )

    for i := 0; i < CAP; i++ {
      fmt.Println( i, <-c )
    }

    quit <- 0
  }()

  fibonacciWithDefault( c, c1, quit )
}

func fibonacciWithoutDefault( c, quit chan int ) {
  x, y := 0, 1

  for {
    select {
    case c <- x:
      x, y = y, x + y
    case <- quit:
      fmt.Println( "quit" )
      return
    }
  }
}

func callFibonacciWithoutDefault() {
  c    := make( chan int )
  quit := make( chan int )

  go func() {
    for i := 0; i < CAP; i++ {
      fmt.Println( i, <-c )
    }

    quit <- 0
  }()

  fibonacciWithoutDefault( c, quit )
}