Go Programming Language Lecture Notes PDF

UNIVERSITAS SCIENTIARUM SZEGEDIENSIS SZEGEDI TUDOMÁNYEGYETEM Szoftverfejlesztés Tanszék Concurrent and parallel constructs in Go Dr. Kertész Attila keratt (at) inf.u-szeged.hu https://go.dev/doc/gopher/fiveyears.jpg ...

UNIVERSITAS SCIENTIARUM SZEGEDIENSIS SZEGEDI TUDOMÁNYEGYETEM Szoftverfejlesztés Tanszék Concurrent and parallel constructs in Go Dr. Kertész Attila keratt (at) inf.u-szeged.hu https://go.dev/doc/gopher/fiveyears.jpg  History of Go SZEGEDI TUDOMÁNYEGYETEM  1978: Tony Hoare published Communicating Sequential Processes (CSP) with a mathematical foundation, as a Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS new basis for concurrent programming languages  Occam is built upon the CSP model, designed in Szoftverfejlesztés parallel through the 80s by David May in INMOS (UK) for Transputer microprocessors  v2.1 published in 1994, latest version of KRoC in 2006  Occam has been used since for safety-critical systems, e.g. in CERN  Go: designed by Google from 2007, also built on CSP, published in 2012  Written in Go: Dropbox, Docker, Netflix, Uber 2  Syntax of Go aka Golang (.org) SZEGEDI TUDOMÁNYEGYETEM  Similar to C Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS  Statically typed, procedural language  Basic types: bool, int, float, byte, string (, pointer-nil) Szoftverfejlesztés var i int var s string = “string” OR s := “string” const Pi = 3.14 var a int OR a := make([]int, 10) array len(a) → 10 fmt.Println(s[1:4]) → “tri” slice 3  Syntax of Go – Control constructs SZEGEDI TUDOMÁNYEGYETEM  for:  while (for!): Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS Szoftverfejlesztés package main func main() { import "fmt" (Init statement) sum := 1 Condition exp. for sum < 1000 func main() { (Post st.) { sum := 0 sum += sum } for i := 0; i < 10; i++ { fmt.Println(sum) sum += i } } fmt.Println(sum) } 4  Syntax of Go – Control constructs SZEGEDI TUDOMÁNYEGYETEM (Init statement  if: return value type Tanszék before condition) UNIVERSITAS SCIENTIARUM SZEGEDIENSIS function Szoftverfejlesztés func pow(x, n, lim float64) float64 { if v := math.Pow(x, n); v < lim { return v } else { fmt.Printf("%g >= %g\n", v, lim) } // can't use v here, though return lim } 5  Syntax of Go – Control constructs SZEGEDI TUDOMÁNYEGYETEM Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS  switch: Szoftverfejlesztés switch os := runtime.GOOS; os { case "darwin": fmt.Println("OS X.") case "linux": fmt.Println("Linux.") default: // freebsd, openbsd, // plan9, windows... fmt.Printf("%s.\n", os) } 6  Syntax of Go – Control constructs SZEGEDI TUDOMÁNYEGYETEM  defer: Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS  - evaluated immediately, but the function call is not executed until the surrounding function returns Szoftverfejlesztés - deferred function calls are pushed onto a stack, and are executed in last-in-first-out package main import "fmt" func main() { defer fmt.Println("world") fmt.Println("hello") } 7  Syntax of Go – data types SZEGEDI TUDOMÁNYEGYETEM  type, struct, interface, method in Go: type geometry interface { func (c circle) perim() float64 { area() float64 return 2 * math.Pi * c.radius perim() float64 Tanszék } UNIVERSITAS SCIENTIARUM SZEGEDIENSIS } func measure(g geometry) { type rect struct { Szoftverfejlesztés fmt.Println(g) width, height float64 fmt.Println(g.area()) } fmt.Println(g.perim()) type circle struct { } radius float64 } func main() { r := rect{width: 3, height: 4} func (r rect) area() float64 { c := circle{radius: 5} return r.width * r.height } measure(r) func (r rect) perim() float64 { measure(c) return 2*r.width + 2*r.height } } func (c circle) area() float64 { return math.Pi * c.radius * c.radius } 8  Concurrency in Go SZEGEDI TUDOMÁNYEGYETEM  Threads are represented by goroutines in Go  Goroutines are lightweight threads, assigned to OS Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS processes with the Go runtime system Szoftverfejlesztés  go: main() func say(s string) { P1 fmt.Println(s) } func main() { P2 say("Hello") // P1 go say("world") // P2 main ends say("!") // P1 } Hello ! 9  Concurrency in Go SZEGEDI TUDOMÁNYEGYETEM  main() need to wait for the end of P2 (anonymous function)  Can be done with WaitGroups Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS func main() { var wg sync.WaitGroup Szoftverfejlesztés fmt.Println("hello") // P1 main() wg.Add(1) add one process to WG go func() { // P2 P1 time.Sleep(1) fmt.Println("world") P2 wg.Done() finish one process in WG }() wg.Wait() wait for WG fmt.Println("!") // P1 } Hello main() ends world ! 10  Channels in Go SZEGEDI TUDOMÁNYEGYETEM  Go channels are:  Typed, bidirectional, and synchronous (by default) Tanszék UNIVERSITAS SCIENTIARUM SZEGEDIENSIS ch := make(chan int) Szoftverfejlesztés ch