在运行 httpd 服务的 Linux 网络服务器上，执行以下命令可获得以下结果：
service httpd status
有人非常熟悉这些州吗？
__C__W_KW__W....K._K..KW.....W..R.W.............................
................................................................
................................................................
................................................................
Scoreboard Key:
"_" Waiting for Connection, "S" Starting up, "R" Reading Request,
"W" Sending Reply, "K" Keepalive (read), "D" DNS Lookup,
"C" Closing connection, "L" Logging, "G" Gracefully finishing,
"I" Idle cleanup of worker, "." Open slot with no current process
我想知道 C 与 G 、 S 与 R 以及 . 与 _ 等状态之间的区别？