fix race condition in config updating

config/config.go

@@ -35,13 +35,20 @@ func Global() *Config {
 	return cfg
 }
 
-func SetGlobal(c *Config) {
+func Set(c *Config) {
 	globalMux.Lock()
 	defer globalMux.Unlock()
 
 	global = c
 }
 
+func OnUpdate(f func(c *Config) error) error {
+	globalMux.Lock()
+	defer globalMux.Unlock()
+
+	return f(global)
+}
+
 type LogConfig struct {
 	Output   string             `yaml:",omitempty" json:"output,omitempty"`
 	Level    string             `yaml:",omitempty" json:"level,omitempty"`