lib/writeconcurrencylimiter: moved the error generation from incConcurrency() to the caller place

lib/writeconcurrencylimiter/concurrencylimiter.go

@@ -62,7 +62,14 @@ var readerPool sync.Pool
 func (r *Reader) Read(p []byte) (int, error) {
 	n, err := r.r.Read(p)
 	if !r.increasedConcurrency {
-		if err := incConcurrency(); err != nil {
+		if !incConcurrency() {
+			err = &httpserver.ErrorWithStatusCode{
+				Err: fmt.Errorf("cannot process insert request for %.3f seconds because %d concurrent insert requests are already executed. "+
+					"Possible solutions: to reduce workload; to increase compute resources at the server; "+
+					"to increase -insert.maxQueueDuration; to increase -maxConcurrentInserts",
+					maxQueueDuration.Seconds(), *maxConcurrentInserts),
+				StatusCode: http.StatusServiceUnavailable,
+			}
 			return 0, err
 		}
 		r.increasedConcurrency = true
@@ -87,12 +94,12 @@ var (
 	concurrencyLimitChOnce sync.Once
 )
 
-func incConcurrency() error {
+func incConcurrency() bool {
 	concurrencyLimitChOnce.Do(initConcurrencyLimitCh)
 
 	select {
 	case concurrencyLimitCh <- struct{}{}:
-		return nil
+		return true
 	default:
 	}
 
@@ -101,17 +108,11 @@ func incConcurrency() error {
 	select {
 	case concurrencyLimitCh <- struct{}{}:
 		timerpool.Put(t)
-		return nil
+		return true
 	case <-t.C:
 		timerpool.Put(t)
 		concurrencyLimitTimeout.Inc()
-		return &httpserver.ErrorWithStatusCode{
-			Err: fmt.Errorf("cannot process insert request for %.3f seconds because %d concurrent insert requests are already executed. "+
-				"Possible solutions: to reduce workload; to increase compute resources at the server; "+
-				"to increase -insert.maxQueueDuration; to increase -maxConcurrentInserts",
-				maxQueueDuration.Seconds(), *maxConcurrentInserts),
-			StatusCode: http.StatusServiceUnavailable,
-		}
+		return false
 	}
 }