split ptr retrieval and incrementation

metrics.go

@@ -31,7 +31,8 @@ func (m *Metrics) incRequestsTotal(method string) {
 
 // incErrorsTotal increases the counter for this error atomically by one.
 func (m *Metrics) incErrorsTotal(err HTTPError) {
-	m.ErrorsTotal.incError(err)
+	ptr := m.ErrorsTotal.retrievePointerFor(err)
+	atomic.AddUint64(ptr, 1)
 }
 
 // incBytesReceived increases the number of received bytes atomically be the
@@ -86,15 +87,17 @@ func newErrorsTotalMap() ErrorsTotalMap {
 	}
 }
 
-// incErrorsTotal increases the counter for this error atomically by one.
-func (e *ErrorsTotalMap) incError(err HTTPError) {
-	// The goal is to have a valid ptr to the counter for this err
+// retrievePointerFor returns (after creating it if necessary) the pointer to
+// the counter for the error.
+func (e *ErrorsTotalMap) retrievePointerFor(err HTTPError) *uint64 {
 	e.RLock()
 	ptr, ok := e.m[err]
 	e.RUnlock()
-	if !ok {
-		// The ptr does not seem to exist for this err
-		// Hence we create it (using a write lock)
+	if ok {
+		return ptr
+	}
+
+	// For pointer creation, a WriteLock is required
 	e.Lock()
 	// We ensure that the ptr wasn't created in the meantime
 	if ptr, ok = e.m[err]; !ok {
@@ -102,9 +105,7 @@ func (e *ErrorsTotalMap) incError(err HTTPError) {
 		e.m[err] = ptr
 	}
 	e.Unlock()
-	}
-	// We can then increase the counter
-	atomic.AddUint64(ptr, 1)
+	return ptr
 }
 
 // Load retrieves the map of the counter pointers atomically