Concurrency Basics

Buffered Channel

A buffered channel can hold a small value before it is received.

buffered channel A buffered channel can act as a deterministic handoff queue when its capacity is large enough.

Buffered Channel

second
buffered_channel.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var second = "green"
	queue := make(chan string, 2)

	queue <- "red"
	queue <- second

	firstOut := <-queue
	secondOut := <-queue
	fmt.Println("first=", firstOut)
	fmt.Println("second=", secondOut)
	fmt.Println("capacity=", cap(queue))
}

package main

import "fmt"

func main() {
	var second = "blue"
	queue := make(chan string, 2)

	queue <- "red"
	queue <- second

	firstOut := <-queue
	secondOut := <-queue
	fmt.Println("first=", firstOut)
	fmt.Println("second=", secondOut)
	fmt.Println("capacity=", cap(queue))
}

package main

import "fmt"

func main() {
	var second = "yellow"
	queue := make(chan string, 2)

	queue <- "red"
	queue <- second

	firstOut := <-queue
	secondOut := <-queue
	fmt.Println("first=", firstOut)
	fmt.Println("second=", secondOut)
	fmt.Println("capacity=", cap(queue))
}

  1. second ← "green", queue ← (chan string)(⟨addr A⟩), firstOut ← "red"

    5func main() {6  var second→ "green" = "green" //@second="blue", "yellow"7  queue→ (chan string)(⟨addr A⟩) := make(chan string, 2)89  queue(chan string)(⟨addr A⟩) <- "red"10  queue(chan string)(⟨addr A⟩) <- second"green"1112  firstOut→ "red" := <-queue(chan string)(⟨addr A⟩)13  secondOut→ "green" := <-queue(chan string)(⟨addr A⟩)14  fmt.Println("first=", firstOut"red")15  fmt.Println("second=", secondOut"green")16  fmt.Println("capacity=", cap(queue(chan string)(⟨addr A⟩)))17}
    outputfirst= red
second= green
capacity= 2

  1. second ← "blue", queue ← (chan string)(⟨addr A⟩), firstOut ← "red"

    5func main() {6  var second→ "blue" = "blue"7  queue→ (chan string)(⟨addr A⟩) := make(chan string, 2)89  queue(chan string)(⟨addr A⟩) <- "red"10  queue(chan string)(⟨addr A⟩) <- second"blue"1112  firstOut→ "red" := <-queue(chan string)(⟨addr A⟩)13  secondOut→ "blue" := <-queue(chan string)(⟨addr A⟩)14  fmt.Println("first=", firstOut"red")15  fmt.Println("second=", secondOut"blue")16  fmt.Println("capacity=", cap(queue(chan string)(⟨addr A⟩)))17}
    outputfirst= red
second= blue
capacity= 2

  1. second ← "yellow", queue ← (chan string)(⟨addr A⟩), firstOut ← "red"

    5func main() {6  var second→ "yellow" = "yellow"7  queue→ (chan string)(⟨addr A⟩) := make(chan string, 2)89  queue(chan string)(⟨addr A⟩) <- "red"10  queue(chan string)(⟨addr A⟩) <- second"yellow"1112  firstOut→ "red" := <-queue(chan string)(⟨addr A⟩)13  secondOut→ "yellow" := <-queue(chan string)(⟨addr A⟩)14  fmt.Println("first=", firstOut"red")15  fmt.Println("second=", secondOut"yellow")16  fmt.Println("capacity=", cap(queue(chan string)(⟨addr A⟩)))17}
    outputfirst= red
second= yellow
capacity= 2