code: func (f *FileLogger) fileCheck() {
  	defer func() {
  		if err := recover(); err != nil {
  			f.lg.Printf("FileLogger's FileCheck() catch panic: %v\n", err)
  		}
  	}()
  
  	if f.isMustSplit() {
  		f.mu.Lock()
  		defer f.mu.Unlock()
  
  		f.split()
  	}
  }
docs: // If the current fileLogger need to split, just split