Limiting number of goroutines (concurrency) in golang

limit-goroutines.go

concurrency := 10 // 10 is max concurrency
sem := make(chan bool, concurrency)
urls := []string{"url1", "url2"}
for _, url := range urls {
    sem <- true // mark one as running (will block when full)
    go func(url) {
        defer func() { <-sem }() // mark one as completed
        // Do something with the url
    }(url)
}

//to make sure we wait for all of them to finish
for i := 0; i < cap(sem); i++ {
    sem <- true
}