mysql - Online Game Login Design -

i working on online game , have design problem login server. each player must logged-in 1 client, if tries open client , tries login should tell account logged in client.

that works, problem when tries login 2 clients @ exact same time both clients go through, causing account logged-in in 2 different places. not wan't.

my current approach (i'm using golang):

var onlogin map[string]uint16 = make(map[string]uint16)  func login(data []byte) []byte {     username := cstring(data[8:23])     password := cstring(data[24:39])      // check if trying login     _, loggingin := onlogin[username]     if loggingin {         fmt.println("possible double connect attempt", username)         return nil     }      (...check if correct login info...)     (...check if user logged in...)      // remove list before returning     delete(onlogin, username)      (...build , send packet client if login success or fail...) 

it helps (a bit) when able press login button on 2 clients @ inhumanly exact same time still goes through. maybe design flawed? advice? cheers!

your onlogin needs mutex, if run code -race tell there's race.

race detector must read.

// edit example:

var onlogin = struct {     sync.mutex     m map[string]bool }{m: map[string]bool{}}  func login(data []byte) []byte {     username := cstring(data[8:23])     password := cstring(data[24:39])     onlogin.lock()     defer onlogin.unlock()      if _, loggingin := onlogin.m[username]; loggingin {         fmt.println("possible double connect attempt", username)         return nil     }     ///.... }