什么时候可以使用golang闭包之外的值？

var loggers []*logOutput = nil

func init() {
    loggers = make([]*logOutput, int(LOGGER_USAGE_TYPE_COUNT))
}

func ABC() {
    loggers[loggerType].ticker = time.NewTicker(time.Second * 
    time.Duration(logRotateCheckInterval))
    go func() {
        defer RecoverFunc()
        for {
            <-loggers[loggerType].ticker.C
            loggers[loggerType].checkAndRotateLogFile()
        }
    }()
}

<-loggers[loggerType].ticker.C will sometimes panic. And there's only one goroutine modifying loggers[loggerType] and loggers[loggerType].ticker. I found that when panic happens, loggers[loggerType].ticker is nil, which makes me feel that the goroutine use the value of loggers[loggerType].ticker before loggers[loggerType].ticker = time.NewTicker(time.Second * time.Duration(logRotateCheckInterval)) is executed.

Could anyone explain when the closure takes the value of a outside variable? I change the logger as a pointer variable to the goroutine func as a solution