protect master connection by lock, retry when IOError
protect master connection by lock, retry when IOError

Mignet/dpark,veritynoob/dpark,mageia/dpark,douban/dpark,douban/dpark,oceanjack/dpark,fe11x/dpark,yhj630520/dpark,windreamer/dpark,yanheven/dpark,dogeyes/dpark,daishaowei/dpark,zzl0/dpark,windreamer/dpark,dogeyes/dpark,daishaowei/dpark,smarthomekit/dpark,windreamer/dpark,junmoa/dpark,fe11x/dpark,yhj630520/dpark,304471720/dpark,douban/dpark,quxiaolong1504/dpark,ee08b397/dpark,yhj630520/dpark,quxiaolong1504/dpark,veritynoob/dpark,yanheven/dpark,zzl0/dpark,windreamer/dpark,smarthomekit/dpark,304471720/dpark,veritynoob/dpark,junmoa/dpark,Mignet/dpark,smarthomekit/dpark,douban/dpark,oceanjack/dpark,douban/dpark,mageia/dpark,dogeyes/dpark,304471720/dpark