the front waiter should try to notify waiters

Author: zhiqiangxu

semaphore/semaphore.go

@@ -67,7 +67,11 @@ func (s *Weighted) Acquire(ctx context.Context, n int64) error {
 // fix up the queue, just pretend we didn't notice the cancelation.
 err = nil
 default:
+isFront := s.waiters.Front() == elem
 s.waiters.Remove(elem)
+if isFront && s.size > s.cur {
+s.notifyWaiters()
+}
 }
 s.mu.Unlock()
 return err
@@ -97,6 +101,11 @@ func (s *Weighted) Release(n int64) {
 s.mu.Unlock()
 panic("semaphore: released more than held")
 }
+s.notifyWaiters()
+s.mu.Unlock()
+}
+
+func (s *Weighted) notifyWaiters() {
 for {
 next := s.waiters.Front()
 if next == nil {
@@ -123,5 +132,4 @@ func (s *Weighted) Release(n int64) {
 s.waiters.Remove(next)
 close(w.ready)
 }
-s.mu.Unlock()
 }