Goroutines and Channels

Part of the Go course

Your program needs to download twenty files. Written the ordinary way, it downloads the first one, waits, downloads the second one, waits, and so on. Almost all of that time is spent doing nothing at all, just waiting for a network that is slower than your processor by a factor of millions. The work would finish twenty times sooner if the waiting overlapped.

Doing several things at once is the oldest hard problem in programming, and most languages make it genuinely difficult. Go was designed around it, and this is the lesson where that shows. You get two ideas. A goroutine is a piece of your program that runs alongside the rest of it. A channel is a pipe for handing values from one goroutine to another, safely, without you having to arrange any locking.