learn_golang/learn_go_with_tests/my_select/racer.go

package my_select

import (
	"fmt"
	"net/http"
	"time"
)

var defaultTimeout time.Duration = 10 * time.Second

func Racer(a, b string) (winner string, err error) {
	return ConfigurableRacer(a, b, defaultTimeout)
}

func ConfigurableRacer(a string, b string, timeout time.Duration) (winner string, err error) {
	// aDuration := measureResponseTime(a)
	// bDuration := measureResponseTime(b)

	// if aDuration < bDuration {
	// 	return a
	// }

	// return b

	select {
	// Here we are simply waiting on the channel closing out
	// The first one that does so will return it's url

	// These are blocking operations because they are unbuffered channels.
	// This works though because `select` allows us to wait on multiple channels
	case <-ping(a):
		return a, nil
	case <-ping(b):
		return b, nil
	// Super handy function during select, returns a channel, waits the timeout, then
	//sends the current time that it was triggered at.
	// Helps get us out of a blocking case.
	case <-time.After(timeout):
		return "", fmt.Errorf("timed out waiting for %s and %s", a, b)
	}
}

// In our case, we don't care what type is sent to
//the channel, we just want to signal we are done
// and closing the channel works perfectly!

// a chan struct{} is the smallest data type available
// from a memory perspective

func ping(url string) chan struct{} {
	// 	Notice how we have to use make when creating a channel; rather than say var ch chan struct{}. When you use var the variable will be initialised with the "zero" value of the type. So for string it is "", int it is 0, etc.

	// For channels the zero value is nil and if you try and send to it with <- it will block forever because you cannot send to nil channels
	ch := make(chan struct{})
	go func() {
		http.Get(url)
		close(ch)
	}()
	return ch
}

// func measureResponseTime(url string) time.Duration {
// 	start := time.Now()
// 	http.Get(url)
// 	return time.Since(start)
// }