mac进程能打开的最大文件数,默认只有256
$ulimit -n
256
这会导致go的服务端运行的时候，如果同时连接的客户端太多，会报错：
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 20ms
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 40ms
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 80ms
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 160ms
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 320ms
2015/08/31 11:47:58 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 640ms
2015/08/31 11:47:59 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
2015/08/31 11:48:00 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
2015/08/31 11:48:01 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
2015/08/31 11:48:02 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
2015/08/31 11:48:03 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
2015/08/31 11:48:04 http: Accept error: accept tcp [::]:12621: too many open files; retrying in 1s
解决办法：
mac修改进程能打开的最大文件数：1.
$su 切换到root账户
#launchctl limit maxfiles 99999 99999
#ulimit -n 99999
#exit
2.确认修改生效
$ulimit -n
99999
3.每个窗口的服务都必须在重设ulimit -n之后，重启才生效!
4.举例
cd $GOPATH/src/car_server/bentchmark
go run main.go 2>2.log &
tail -f 2.log
grep "connect ok" 2.log | wc -l