fix golint issues in core/syncx (#526)

core/syncx/resourcemanager.go

@@ -7,12 +7,14 @@ import (
 	"github.com/tal-tech/go-zero/core/errorx"
 )
 
+// A ResourceManager is a manager that used to manage resources.
 type ResourceManager struct {
 	resources   map[string]io.Closer
 	sharedCalls SharedCalls
 	lock        sync.RWMutex
 }
 
+// NewResourceManager returns a ResourceManager.
 func NewResourceManager() *ResourceManager {
 	return &ResourceManager{
 		resources:   make(map[string]io.Closer),
@@ -20,6 +22,7 @@ func NewResourceManager() *ResourceManager {
 	}
 }
 
+// Close closes the manager.
 func (manager *ResourceManager) Close() error {
 	manager.lock.Lock()
 	defer manager.lock.Unlock()
@@ -34,6 +37,7 @@ func (manager *ResourceManager) Close() error {
 	return be.Err()
 }
 
+// GetResource returns the resource associated with given key.
 func (manager *ResourceManager) GetResource(key string, create func() (io.Closer, error)) (io.Closer, error) {
 	val, err := manager.sharedCalls.Do(key, func() (interface{}, error) {
 		manager.lock.RLock()