How I Learn Golang Goroutines in 1 Day

> Learn Golang Basics here

Goroutines & Concurrent

Goroutines

View day2.go file

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package main

import (
"fmt"
"time"
)

func main() {
chanChanChanChan()
bufferedChan()
synchronizeTask()
pingPongGame()
selectChannel()
outOfTime()
nonBlockingChannelWithSelect()
closeChannel()
rangeOverChannel()
doSomethingLater()
doInterval()
}

func chanChanChanChan() {
chan1 := make(chan string)
chan2 := make(chan string)

// By default sends and receives block until both the sender and receiver are ready.
go func() {
fmt.Println("[1] Passing chan2 !")
chan2 <- "Chan2"
fmt.Println("[1] Passed chan2 !")
}()

go func() {
fmt.Println("[1] Receiving chan2 !")
chan2Msg := <-chan2
fmt.Println("[1] Received chan2 !")

chan2Msg += " Chan1"

fmt.Println("[1] Passing chan1 !")
chan1 <- chan2Msg
fmt.Println("[1] Passed chan1 !")
}()

fmt.Println("[1] Waiting for chan1 message ...")
msg := <-chan1
fmt.Println("[1] Message from goroutines :", msg)
}

func bufferedChan() {
chan1 := make(chan string, 2) // second parameter is number of messages the channel will handle, it creates Buffered Channel

go func() {
fmt.Println("[2] Passing chan2 !")
chan1 <- "Chan2" // Buffered Chan doesn't need to wait concurrent receiving
fmt.Println("[2] Passed chan2 !")
}()

go func() {
fmt.Println("[2] Passing chan1 !")
chan1 <- "Chan1" // Buffered Chan doesn't need to wait concurrent receiving
fmt.Println("[2] Passed chan1 !")
}()

fmt.Println("[2] Waiting for chan1 message ...")
time.Sleep(time.Second * 3) // Wait 3 seconds to wait message passing to buff chan
msg := <-chan1
msg += <-chan1
fmt.Println("[2] Message from buffered chan :")
}

func synchronizeTask() {
done := make(chan bool)

go func(ok chan bool) {
fmt.Println("[3] Working ...")
time.Sleep(time.Second)
fmt.Println("[3] Done ...")

ok <- true
}(done)

<-done
fmt.Println("[3] Lets relax !")
}

// Channel direction
func ping(rchan chan<- string, msg string) {
rchan <- msg
}

func pong(rchan <-chan string, schan chan<- string) {
tmp := <-rchan
schan <- tmp
}

func pingPongGame() {
chan1 := make(chan string, 1)
chan2 := make(chan string, 1)

ping(chan1, "Game over !")
pong(chan1, chan2)
pingPongMsg := <-chan2
fmt.Println("[4] Ping pong message :", pingPongMsg)
}

func selectChannel() {
c1 := make(chan string)
c2 := make(chan string)

go func() {
time.Sleep(time.Second)
c1 <- "msg1"
}()

go func() {
time.Sleep(time.Second * 2)
c2 <- "msg2"
}()

// Wait multi channel, whole func take ~2 seconds because of sleeping concurrently
for i := 0; i < 2; i++ {
select {
case msg1 := <-c1:
fmt.Println("[5] Received :", msg1)
case msg2 := <-c2:
fmt.Println("[5] Received :", msg2)
}
}
}

func outOfTime() { // Timeout using select channel
chan1 := make(chan string)

go func() {
time.Sleep(time.Second * 2)
chan1 <- "here result after 2 seconds"
}()

select {
case msg := <-chan1:
fmt.Println("[6] Message from chan1", msg)
case <-time.After(time.Second):
fmt.Println("[6] Your time is out ! You only have 1 second !")
}
}

func nonBlockingChannelWithSelect() {
chan1 := make(chan string)

select {
case msg := <-chan1:
fmt.Println("[7] Ahh... got it !", msg)
default:
fmt.Println("[7] Nothing here !")
}
}

func closeChannel() {
jobs := make(chan string, 3)
done := make(chan bool)

go func() {
for {
j, more := <-jobs
if more {
fmt.Println("[8] received a job", j)
} else {
fmt.Println("[8] received all jobs")
done <- true
}
}
}()

for i := 0; i < 3; i++ {
jobs <- "hahaha"
fmt.Println("[8] sent a job")
}
close(jobs)
fmt.Println("[8] sent all jobs")

<-done
}

func rangeOverChannel() {
chan1 := make(chan string, 3)
chan1 <- "1"
chan1 <- "2"
chan1 <- "3"

close(chan1)
for msg := range chan1 {
fmt.Println("[9] range over :", msg)
}
}

func doSomethingLater() {
timer1 := time.NewTimer(time.Second * 2)

<-timer1.C
fmt.Println("[10] timer1 is expired")

timer2 := time.NewTicker(time.Second * 2)
go func() {
<-timer2.C
fmt.Println("[10] timer2 is expired")
}()
timer2.Stop()
fmt.Println("[10] timer2 is stopped")
}

func doInterval() {
ticker := time.NewTicker(time.Millisecond * 500)
go func() {
for t := range ticker.C {
fmt.Println("[11] do job interval at", t)
}
}()
time.Sleep(time.Second * 3)
ticker.Stop()
fmt.Println("[11] Ticker is stopped")
}

Ref:

  • Lesson structure by gobyexample(dot)com
  • Photo by tensor-programming(dot)com

How I Learn Golang Basics in 1 Day

golang

Structure is based on Learn Go in Y Minutes

Install Go

Follow this guide : https://golang.org/doc/install

Compile and Run go code every 1 second

1
$ watch -d -t -n 1 go run day1.go

Use VisualStudio Code

Basics

View day1.go file

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package main

import (
"fmt" // Formatting standard library
m "math" // Alias an imported lib
"strconv" // String conversion lib
"net/http"
"io/ioutil"
)

func main() {
fmt.Println("Hello World ! go go go")

moveIt()
}

func moveIt() {
var x float64 // Declare variable
x = 3 // Assign it to a value
y := 4. // Declare and assign in 1-line
fmt.Println(x, y, pythagore(x, y))

goToTypes()
followTheFlow()
hmmmLikeClosure()
doItTommorow()
smashInterfaces()
learnVariadicParams("hello", "khanhicetea", "a human")
oopsSomethingWrong()
goToWWW()

fmt.Println("\n-------- THE END --------\n")
}

func pythagore(a float64, b float64) (float64) { // func [function name]( ...paramers ) (return types)
return m.Sqrt(a * a + b * b)
}

func goToTypes() {
a1 := 1 // Int
a2 := 2.3 // Float
a3 := "ほげほげ !!!" // Japanese string, lol
a4 := 's' // Char, alias for int32, hold unicode code
a5 := `This is "quoted" string,
with new line and tab`
a6 := byte('\n') // ASCII char, uint8
fmt.Println(a1, a2, a3, a4, a5, a6)

// Arrays
var a7 [3]int // declare fixed array of 3 integer items
a7[0] = 12
a7[1] = 23
a7[2] = 34

a8 := [...]int{1,1,2,3,5,8,13} // no need count array length to declare
fmt.Println(a7, a8)

// Slices
a9 := []int{1,2,3}
a10 := make([]int, 3) // Allocate slide 3 ints, 0 intial value

var a11 [][]float64 // declare only
a12 := []byte("hello") // convert string to slice of chars

fmt.Println(a9, a10, a11, a12)

a9 = append(a9, 4, 5, 6) // append 3 items
fmt.Println(a9)

a13 := []int{10, 11}
a9 = append(a9, []int{7, 8, 9}...) // merge 2 slices with suffix ...
a9 = append(a9, a13...)
fmt.Println(a9)

a14 := "ignored value"
_ = a14 // Ignore by _ , unused variable cause error

a15 := map[string]int{
"one": 1,
"two": 2,
"there": 3,
}
a15["four"] = 4

fmt.Println(a15, a15["two"])

a16, a17 := memoryZoo()
fmt.Println(*a16, a17)
}

func memoryZoo() (a, b *int) {
s := make([]int, 5)
s[3] = 4
o := 123

a = &s[3] // can assign to returned var
b = &o // & is ref memory address, like a pointer in C

return // no need pass returned vars here
}

func followTheFlow() {
if 1 + 1 == 2 {
fmt.Println("Hmm .. it must me 10 ! Ya know ;)")
}

if 1 > 2 {
fmt.Println("Universe goes down !")
} else if 42 > 24 {
fmt.Println("node_modules size is heavier than backhole !")
} else {
fmt.Println("Okay, I'm drunk")
}

a18 := 3

switch a18 {
case 1:
case 2: // cases don't fall down like C-like lang
case 3:
fmt.Println("Three !!")
default:
}

for i := 0; i < 3; i++ {
fmt.Println(i)
}

numbers := map[string]int{
"a": 1,
"b": 2,
"c": 5,
}

for key, num := range numbers { // loop a map
fmt.Println(key, num)
}

for _, num := range numbers { // loop a map, no need key
fmt.Println(num)
}

if a14 := 3 * 4; a14 < 13 { // last statement is condition
fmt.Println("3 * 4 < 13")
}
}

func hmmmLikeClosure() {
a15 := add(15)
a16 := a15(5)
fmt.Println(a16)
}

func add(x int) func(y int) int {
return func (y int) int {
return x + y
}
}

func doItTommorow() {
a17 := testMyCode()
fmt.Println(a17)
}

func testMyCode() int {
defer fmt.Println("456") // defer : run before return
fmt.Println("0")
defer fmt.Println("789") // defer : run in LIFO order.
return 123
}

type Stringer interface {
String() string
}

type Point struct {
x, y int
}

func (p Point) String() string {
return fmt.Sprintf("(%d, %d)", p.x, p.y)
}

func smashInterfaces() {
p := Point{3, 4}
fmt.Println(p.String())

var i Stringer // Declare i as Stringer interface
i = p // Point implement Stringer interface
fmt.Println(i.String())
}

func learnVariadicParams(strings ...interface{}) {
// Iterate each value of the variadic.
for _, s := range strings {
fmt.Println("param :", s)
}

// Pass variadic value as a variadic parameter.
fmt.Println("params :", fmt.Sprintln(strings...))
}

func oopsSomethingWrong() {
numbers := map[string]int{
"a": 1,
"b": 2,
"c": 5,
}

if x, ok := numbers["d"]; !ok {
fmt.Println("Oops something went wrong !!!")
} else {
fmt.Println(x)
}

a18 := "1.2"
if _, err := strconv.ParseInt(a18, 10, 8); err != nil { // check if err
fmt.Println("true === false")
}
}

func goToWWW() {
go func() {
err:= http.ListenAndServe("127.0.0.1:8888", &WebServer{"KhanhIceTea server"})
fmt.Println(err)
}()

crawlWeb()
}

type WebServer struct {
name string
}

func (ws *WebServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("Hello from "))
w.Write([]byte(ws.name))
}

func crawlWeb() {
resp, err := http.Get("http://127.0.0.1:8888")
fmt.Println(err)
defer resp.Body.Close() // Close body stream
body, err := ioutil.ReadAll(resp.Body)
fmt.Println("\nWebServer said : `%s`", string(body))
}

Please ! Teach me !

> Learn Golang Goroutines and Concurrent here