为什么不使用锁来同步日志包

Question

I'm reading log source code,I'm confused in here:

// SetOutput sets the output destination for the standard logger.
func SetOutput(w io.Writer) {
    std.mu.Lock()
    defer std.mu.Unlock()
    std.out = w
}

// Flags returns the output flags for the standard logger.
func Flags() int {
    return std.Flags()
}

// SetFlags sets the output flags for the standard logger.
func SetFlags(flag int) {
    std.SetFlags(flag)
}

why SetOutPut use mu to lock but SetFlags don't use mu to lock?

Answer 1

SetOutput is altering the internal state of the std default Logger.

log.SetFlags is calling SetFlags on std, which already locks the logger itself.