Pool: notify fewer waiters on returned connection (#559)

Co-authored-by: Stephen Cathcart <stephen.cathcart@neotechnology.com>

neo4j/internal/pool/pool.go

@@ -258,6 +258,17 @@ func (p *Pool) Borrow(
  case <-ctx.Done():
  p.queueMut.Lock()
  p.queue.Remove(e)
+ if len(q.wakeup) == 1 {
+ // We got notified, but are no longer interested.
+ // Ask the next waiter.
+ if e := p.queue.Front(); e != nil {
+ queuedRequest := e.Value.(*qitem)
+ p.queue.Remove(e)
+ queuedRequest.wakeup <- true
+ }
+ p.queueMut.Unlock()
+ continue
+ }
  p.queueMut.Unlock()
  p.log.Warnf(log.Pool, p.logId, "Borrow time-out")
  return nil, &errorutil.PoolTimeout{Err: ctx.Err(), Servers: serverNames}
@@ -425,7 +436,8 @@ func (p *Pool) Return(ctx context.Context, c idb.Connection) {
 
  // Check if there is anyone in the queue waiting for a connection to this server.
  p.queueMut.Lock()
- for e := p.queue.Front(); e != nil; e = e.Next() {
+
+ if e := p.queue.Front(); e != nil {
  queuedRequest := e.Value.(*qitem)
  p.queue.Remove(e)
  queuedRequest.wakeup <- true