Can't figure out why this loop is a data race - go

Question

I have a loop that is apparently causing a data race its near the bottom of this function and I will have it marked:
func (p *PartialParty) SendReadyCheck(party PartialParty) {
msg, err := json.Marshal(&ReadyCheckMsg{"ReadyCheck", ""})
if err != nil {
log.Println(err)
}
for _, member := range party.Members {
member.Conn.send <- msg
}
counter := 0
loopBreaker := true
for {
select {
case <-p.Accept:
counter++
resp, err := json.Marshal(&ReadyCheckMsg{"ReadyAccepted", ""})
if err != nil {
log.Println(err)
}
for _, member := range party.Members {
member.Conn.send <- resp
}
if counter == 2 {
// Create a new party with all members
partyid := PartyID(feeds.NewUUID().String())
db := common.Db()
newParty := &Party{
Active: true,
Members: p.Members,
Broadcast: make(chan []byte),
PartyID: partyid,
}
// Insert the new party into the database
_, err := db.Exec("INSERT INTO party SET party_id = ?, active = ?", partyid.String(), true)
if err != nil {
log.Println(err)
}
// Go through the members and update the database
var wg sync.WaitGroup
for _, member := range party.Members {
wg.Add(1)
m := member
go func() {
_, err := db.Exec("UPDATE party_members SET active = ? WHERE steamid = ?", false, m.SteamID)
if err != nil {
log.Println(err)
}
_, err = db.Exec("INSERT INTO party_members SET belongs_to =?, active = ?, steamid = ?", partyid.String(), true, m.SteamID)
if err != nil {
log.Println(err)
}
wg.Done()
}()
}
// Wait for all the database stuff to finish
wg.Wait()
PHub.AddNewParty(newParty)
loopBreaker = false
break
}
case conn := <-p.Decline:
if conn.Ready {
break
}
conn.Ready = false
conn.InQueue = false
conn.CurrentParty = ""
resp, err := json.Marshal(&ReadyCheckMsg{"ReadyCheckDeclined", ""})
if err != nil {
log.Println(err)
}
p.Accepting = true
identifier := conn.Identifier
if _, ok := party.Members[identifier]; ok {
delete(p.Members, identifier)
}
for _, m := range party.Members {
member := m
member.Conn.send <- resp
}
log.Println("Here")
loopBreaker = false
break
case <-time.After(30 * time.Second):
if counter == 2 {
return
}
p.Accepting = true
failedMsg, err := json.Marshal(&ReadyCheckMsg{"FailedToReady", ""})
if err != nil {
log.Println(err)
}
somebodyDeclinedMsg, err := json.Marshal(&ReadyCheckMsg{"ReadyCheckDeclined", ""})
if err != nil {
log.Println(err)
}
>>>> for _, member := range party.Members { ***<<<< This Line***
m := member
if !m.Conn.Ready {
m.Conn.Ready = false
m.Conn.InQueue = false
m.Conn.CurrentParty = ""
m.Conn.send <- failedMsg
} else {
m.Conn.Ready = false
m.Conn.send <- somebodyDeclinedMsg
}
}
loopBreaker = false
break
}
if !loopBreaker {
break
}
}
}
It is apparently conflicting with this:
// AddNewMember will add a new user to the party
func (p *PartyHub) AddNewMember(member *Member, partyid PartyID) {
p.Lock()
defer p.Unlock()
>>> p.PartialPartys[partyid].Members[member.Conn.Identifier] = member
}
type PartialParty struct {
Accepting bool
Members map[Identifier]*Member
Accept chan *Connection
Decline chan *Connection
PartyID PartyID
sync.Mutex
}
Right now it is impossible to AddNewMember if the goroutine SendReadyCheck is running ``because it is protected by an if statement that checks if the goroutine is running, so I'm not sure why they are saying they are racing each other. Any help on clearing this up would be great. I've tried setting a variable inside the loop to try to get away from it but it doesn't seem to cause it

Answer 1

Right now it is impossible to AddNewMember if the goroutine SendReadyCheck is running ``because it is protected by an if statement that checks if the goroutine is running
You didn't actually show that part of the code, but presumably it's not impossible. What if SendReadyCheck starts running after the if test but before AddNewMember does its modification?