Training Pill 02: Routines and channels in GO

Go is a language:

– Typing: intX and uintX¹, float32/64, byte and rune (aliases of uint8 and int32, used to represent char), boolean, string and complex (similar to float, but for complex numbers).

– Parameter passing by value

– Pointers

• Garbage collector → mark-and-sweep: the objects that can be referenced by the user are marked. After that, the heap is cleared of untagged (unreachable) objects.

Goroutines

We can understand goroutines as execution threads². Let us imagine the case of the following program:

func f(start, end int) {
for i := start; i < end; i++ {
fmt.Println(i) }
}
func main() {
go f(4, 7)
go f(7, 11)
f(1, 4) time.Sleep(time.Second) fmt.Println(“done”)
}

Channels

Channels are the communication mechanism between goroutines. For the above case, let’s imagine that we want to add up the numbers instead of printing them, and send the total to the channel:

var ch = make(chan int, 3)
func f(start, end int) { total := 0
for i := start; i < end; i++ { total += i
}
ch <- total }
func g() {
for n := range ch {
fmt.Println(“Number “, n) }
}
func main() {
defer close(ch)
go f(4, 7)
go f(7, 11)
f(1, 4)
go g() time.Sleep(time.Second) fmt.Println(“done”)
}

The way we use a channel differs depending on the objective we have with it:

– If it is write only, we can indicate ch chan<-

– If it is read only, ch <-chan

– If it is both, ch chan

As for creation

ch := make(chan int) → Unbuffered: blocking until another goroutine receives the value.

ch := make(chan int, 5) → When we know the amount of data we are going to use.