fix(race): include mutex to avoid race conditions in health (#13)

.travis.yml

@@ -6,5 +6,3 @@ install:
   - make deps
 script:
   - make test
-after_success:
-  - bash <(curl -s https://codecov.io/bash)

Makefile

@@ -10,8 +10,4 @@ clean:
 deps: 
 	go mod download
 test:
-	echo "" > coverage.txt
-	for d in $(shell go list ./...); do \
-		go test -race -v -coverprofile=profile.out -covermode=atomic $$d || exit 1; \
-		[ -f profile.out ] && cat profile.out >> coverage.txt && rm profile.out; \
-	done
+	go test -race -cover ./...

server.go

@@ -14,6 +14,7 @@ var mutex sync.Mutex
 
 // Server server representation
 type Server struct {
+	sync.RWMutex
 	name                  string
 	health                *ServerHealth
 	serverSettings        ServerSettings
@@ -70,13 +71,22 @@ func (s *Server) CheckHealth(traceOn bool, logger Logger) {
 	var secondsBehindMaster, openConnections, runningConnections *int
 
 	// prevent concurrently checks on same server (slow queries/network)
-	if s.isChecking {
+	s.RLock()
+	checking := s.isChecking
+	s.RUnlock()
+
+	if checking {
 		return
 	}
 
+	s.Lock()
 	s.isChecking = true
+	s.Unlock()
+
 	defer func() {
+		s.Lock()
 		s.isChecking = false
+		s.Unlock()
 	}()
 
 	if err := s.connectReadUser(traceOn, logger); err != nil {