Tell me about WaitGroup in Go.

In Go, sync.WaitGroup is used to wait for a group of goroutines to finish. It is a convenient way to synchronize parallel tasks.

Main methods:

• Add(int) — increases the counter of goroutines to wait for.
• Done() — decreases the counter, called when a goroutine finishes.
• Wait() — blocks execution until the counter becomes zero.

Example of usage:

var wg sync.WaitGroup

wg.Add(2) // expecting 2 goroutines

go func() {
    defer wg.Done()
    // work of the first goroutine
}()

go func() {
    defer wg.Done()
    // work of the second goroutine
}()

wg.Wait() // wait for both to finish

Thus, WaitGroup helps control the completion of parallel operations.