A WaitGroup waits for a collection of goroutines to finish. The main goroutine calls Add to set the number of goroutines to wait for. Then each of the goroutines runs and calls Done when finished. At the same time, Wait can be used to block until all goroutines have finished.

It's possible to have another goroutine also to wait on this group. The only real constraint is that Add can only be called by the main one.


func (wg *WaitGroup) Add(delta int)

The delta defines how many more - or less - goroutines, the goroutines waiting need to actually wait for. When the counter gets to zero, then all the waiting goroutines get released. If the counter is negative, then Add panics.


It decrements the counter by one.


Blocks the goroutine until the counter of the WaitGroup gets to zero.