type token … type Group … func (g *Group) done() { … } // WithContext returns a new Group and an associated Context derived from ctx. // // The derived Context is canceled the first time a function passed to Go // returns a non-nil error or the first time Wait returns, whichever occurs // first. func WithContext(ctx context.Context) (*Group, context.Context) { … } // Wait blocks until all function calls from the Go method have returned, then // returns the first non-nil error (if any) from them. func (g *Group) Wait() error { … } // Go calls the given function in a new goroutine. // It blocks until the new goroutine can be added without the number of // active goroutines in the group exceeding the configured limit. // // The first call to return a non-nil error cancels the group's context, if the // group was created by calling WithContext. The error will be returned by Wait. func (g *Group) Go(f func() error) { … } // TryGo calls the given function in a new goroutine only if the number of // active goroutines in the group is currently below the configured limit. // // The return value reports whether the goroutine was started. func (g *Group) TryGo(f func() error) bool { … } // SetLimit limits the number of active goroutines in this group to at most n. // A negative value indicates no limit. // // Any subsequent call to the Go method will block until it can add an active // goroutine without exceeding the configured limit. // // The limit must not be modified while any goroutines in the group are active. func (g *Group) SetLimit(n int) { … }