glog.go
func (l *Log) flushAll() {
	// Flush from fatal down, in case there's trouble flushing.
	for s := FatalLog; s >= InfoLog; s-- {
		file := l.file[s]
		if file != nil {
			file.Flush() // ignore error
			file.Sync()  // ignore error
		}
	}
}
func (l *Log) flushAll() {
	// Flush from fatal down, in case there's trouble flushing.
	for s := FatalLog; s >= InfoLog; s-- {
		file := l.file[s]
		if file != nil {
			file.Flush() // ignore error
			file.Sync()  // ignore error
		}
	}
}
// flushAll flushes all the logs and attempts to "sync" their data to disk.
// l.mu is held.