// G3: Wait() // G1 still hasn't run, G3 finds sema == 1, unblocked! Bug.
// Add adds delta, which may be negative, to the WaitGroup counter.
-// If the counter becomes zero, all goroutines blocked on Wait() are released.
+// If the counter becomes zero, all goroutines blocked on Wait are released.
// If the counter goes negative, Add panics.
+//
+// Note that calls with positive delta must happen before the call to Wait,
+// or else Wait may wait for too small a group. Typically this means the calls
+// to Add should execute before the statement creating the goroutine or
+// other event to be waited for. See the WaitGroup example.
func (wg *WaitGroup) Add(delta int) {
if raceenabled {
raceReleaseMerge(unsafe.Pointer(wg))