Parallelism in Go — Part 1: goroutines and WaitGroup

You have a Go program making 10 HTTP calls to an external API. Each call takes about 1 second. Result: your program takes 10 seconds to finish. With goroutines, those 10 calls run at the same time and the whole thing takes 1 second — the duration of the slowest one, not the sum of all of them. That's the promise of concurrency in Go. And unlike most languages where it's a pain to set up (OS threads, manual locks, cascading callbacks), Go makes it accessible from day one. You still need to avoid the classic pitfalls, and there are a few of them. This three-part series starts from scratch: Part 1 : goroutines and sync.WaitGroup Part 2 : channels and the worker pool pattern Part 3 : errors in concurrent context and clean panic handling What is a goroutine? The most honest analogy: think of your browser tabs. Each tab loads its page "at the same time" — YouTube buffers your video while you read an article in another tab. Your CPU isn't truly doing everything at once (well, not entirely), b